Porsche Cayenne Common Problems
Heavy Gear Shifts or Coolant Leak etc?
Listed below are Porsche Cayenne common mechanical problems with their likely resolutions. These are the most frequent Cayenne problems diagnosed by our repair shops over the years.
An accurate diagnosis of an issue by a Porsche mechanic typically saves you time and money – see our guide to local independent Porsche repair shops that can help. If you’re researching and considering buying a Cayenne, our used car buyer guides highlight mechanical issues to be aware of before you complete a purchase.
Check engine light? Scanned the car and not sure what to make of those OBD codes? Our article on how to interpret and make sense of those fault codes may help.
Maintenance rarely solves a problem. However, neglecting maintenance can cause issues – check your last service update with our recommended Cayenne maintenance schedules.
Can’t Find An Answer Below? – Contact Us For More Help
If your Cayenne has mechanical issues that don’t appear here, simply drop us an email via the forms or pop-up contact and we’ll do our best to share a solution with you.
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Symptoms: Cayenne PCM unit restarting every 2-3 minutes, map not loading, loads in wrong language, loads just the Porsche logo screen, turns on and off randomly etc.
Who hasn’t had an issue with the PCM system in their Cayenne?
Many Cayenne owners have reported all sorts of random and weird behavior from the PCM system and in particular PCM3.1 seems to be the main offender. Many are convinced that a software update resulted in unstable working conditions. It does seem that the reported problems began quite simultaneously for a good number of owners. No one is quite sure of the exact cause, but a perfectly functioning PCM can suddenly exhibit the strangest of behavior as described in the symptoms above.
Defining the Issue with the Cayenne PCM
The problems with the PCM can really be categorized in to two groups.
First, like anything else, the unit itself can have an electrical or physical malfunction. Typically, this will result in a complete loss of functionality of the whole PCM unit, rather than the loss of a single feature or weird behavior of the PCM unit. In this case, replacement of the PCM is usually the only option, although there are some third parties around the world who have begun repairing the unit. Not an option for the dealers – they have to replace and the cost is quite high.
For the second set of Cayenne PCM problems that generally fall into the strange behavior category, an old-fashioned Ctrl Alt Del seems to resolve most issues. Some will remember when it was necessary to do this a couple of times a day to a Windows PC, but in this instance, the PCM usually recovers well to an initial start point and then functions normally.
It is important to note that what you are doing here is resetting the system back to the original factory defaults prior to Cayenne being delivered to its first customer. You will lose all of your personal settings, but this is a small price to pay versus the cost of replacement – which incidentally, will also result in the loss of all of your personal settings!
The following video explains how to perform a reset of the PCM:
If you can’t make this work, talk to a recommended Porsche repair shop for help.
Symptoms: Heavy Gear Shifts or Banging Sound From Transmission
Early Porsche Cayenne owners commonly experienced a heavy downshift from the transmission. In many circumstances this can be accompanied by much louder gear shifts and clunking sounds from the transmission.
The problem is often mis-diagnosed as a physical failure in the transmission itself, when the more likely cause is in fact the valve body assembly within the transmission. The valve body is an electro-mechanical device the redirects the pressurized transmission fluid through a valving system to enable the physical gear changes. Failure of the mechanism can lead to some wild gear shifts.
Transmissions in the later cars are very complex and the technology involved is a closely guarded secret. Technicians at Porsche not trained to dissect the transmission and make repairs. Typically, they just replace the transmission. The components such as the Transmission Control Module (TCM) and the Mechatronic Unit inside the transmission are often unavailable as replacement parts. The manufacturers do not want the transmission taken apart.
Thankfully, with the Cayenne, the valve body assembly is available and replacing it typically saves the transmission. In many cases normal smooth gear shifts are returned.
Symptoms: Vibration Under Acceleration or During Low Speed Tight Turns
Many Cayenne owners have experienced vibrations or unsteady acceleration around the 25-35 mph. This is usually subtle initially, but gets steadily worse, especially when moving forward at low speed with the wheels turned tightly. Sometimes, this can also show up as jerking when the PDK is going through 2nd to 3rd gear changes and accelerating between 30-50mph.
The problem stems from the transfer case in the four-wheel drive system and is a regularly reported issue.
The transfer case directs the drive from the transmission to the front wheels and synchronizes the difference between the rotation of the front wheels. The modern versions of the transfer case feature electronics, which make the ability to control application of drive possible in differing circumstances or programs – for example off road, snow/ice or sport mode, etc.
Wear in the transfer case causes a mismatch between the intended wheel speeds during acceleration and the actual wheel speeds. This subsequently shows up as a vibration under acceleration or a jumping or skipping feeling at extreme steering lock.
Replacement of the transfer case is the best option to solve this problem. While the transfer case has been revised a number of times, this issue appears to continue to plague the Cayenne. Seemingly as a result, Porsche recently announced an extension to the warranty period covering the transfer case.
Symptoms: Coolant Leak – Steam – Overheating
A coolant leak can be deadly for any engine – overheating of the engine due to a loss of coolant very quickly does damage that could result in a total failure and an engine replacement being needed. The coolant pipe failure in the early Cayenne typically happened quickly and produced large amounts of steam.
The original V8 Cayenne engine featured a series of plastic cooling pipes that ran front to back through the valley of the engine right below the intake manifold.
Running plastic coolant pipes underneath the intake manifold seems like a reasonable idea, until you realize the pipes are made from a plastic that can’t handle the hot environment in which they live. Once they degrade and a leak starts it quickly speeds to a point where large clouds of steam can be seen billowing from under the hood when the engine is running – steam powered Cayenne!
There is an update kit available to permanently fix this problem and change the plastic pipes to metal ones. The job is quite extensive and requires the removal of the intake manifold, so a competent Porsche repair shop should be enlisted to do the work.
Water Pump Failure
Water pumps and thermostats fail regularly. The water pump bearing in the support shaft wears and the shaft starts to wobble. This develops into a knocking noise sometimes accompanied by a coolant leak. Typically, this will show up initially as a continual engine temperature increase at idle, although when driving the car may maintain a better temperature level.
Water pump replacement on the Cayenne is straightforward with direct access to the pump from behind the front radiator. This is also the location of the thermostat, which also fails regularly.
The thermostat is electronically controlled and reports a fault when a failure occurs. A failed thermostat that is stuck open is not so bad. Consequently, a thermostat that fails in the closed position, can quickly be very detrimental to the engine.
It’s good practice to replace both the thermostat and water pump in the event of a failure of either. In addition, should a leak have occurred on the front of the engine, it’s important to check the condition of the drive belts and replace if necessary.
Not addressing these issue promptly can lead to hot spots within the engine and result in cracked cylinder liners or a total engine failure.
Symptoms: Loss of Coolant, Flashing Coolant Light
The later Cayenne has a series of coolant pipe connectors that are glued into their aluminum housings – great idea! Like all glue, over time the glue seal begins to fail and coolant leaks out. There are two likely spots for this to occur – the front of the engine or the rear of the engine close to the transmission joint.
Front Engine Coolant Leak
The leak at the front of the engine is most likely from the upper front coolant pipe, which slips out of its housing when the glue fails. Porsche revised the design of the replacement part to be bolt in, so the problem should not return. This issue is common and typically runs about $500 in parts.
Rear Engine Coolant Leak
The leak at the rear of the engine is much more of an issue. Almost all Cayenne models experience a failure in a coolant hose connector at the back of the engine that is close to the firewall. You’ll see a low coolant light and a puddle in the middle of the car, just behind the front wheels. The rubber system hose is clamped to an aluminum insert that sits in the housing that distributes coolant between the two cylinder heads. The glue fails on the aluminum insert and coolant leaks out. The replacement part is updated with a screw in insert for the rubber hose to connect to. Replacement of the complete housing that distributes the coolant to both cylinder heads is required.
The problem is getting this new assembly attached to the engine. Porsche recommends engine and transmission removal, which puts the cost for this minor leak into big money territory! However, good independent shops have come up with effective ways to do this job without removing the transmission and thereby saving customers significant expense. If you have this leak, search our Porsche Repair Shop listing to find a locally skilled expert that can solve this problem for you more cost effectively.
Symptoms: Loss of Power, Check Engine Light, Incorrect Valve Lift
At times the V8 engine in the Porsche Cayenne will report a CEL for codes associated with an incorrect valve lift on one of the two cylinder banks. There are two reasons for this – one obvious and one less so.
Valve Lift Solenoid Failure
First, a solenoid controls oil flow to the cams and the regulation of the valve lift that is reported as inconsistent or not correct. On many occasions replacing the solenoid will solve the problem. However, if the solenoid replacement doesn’t solve the problem, you could be left scratching your head as to why the report of incorrect valve lift returns.
The answer lies in a not so obvious location. Valve lift is determined by the front O2 sensor. Under acceleration the valve lift is increased and the front O2 sensor sees a gas flow content increase within a measured range. A failing front O2 sensor will either not see or cannot react in time to the valve lift gas flow change. The slow response from the O2 sensor is not within the tolerance the engine management system requires and therefore a valve lift fault is set. Replacing the front O2 sensor will typically solve this problem.
Symptoms: CEL, Loss of Power, Misfire Under Load
There are multiple reasons why a check engine light can be set for misfires. A code scan can reveal which cylinder is misfiring but not usually exactly why.
CEL – Misfire – Faulty Ignition Coil
The ignition coils on the Porsche Cayenne V8 have been updated a number of times. A single coil failure is typically a sign of more trouble to come from other coils, so it’s usually best practice to update them all. A failing coil typically stops any spark and sets a misfire code with a completely dead cylinder. This will cause rough running, especially at idle.
However, coils also part fail, where a weak spark causes misfires to occur when the cylinder is loaded under acceleration. Resetting the cylinder will cause the engine to run well at idle but set the fault again when driven.
CEL – Misfire – Worn Spark Plugs
Service intervals between spark plug changes can seem rather long, considering the duty cycle required from a plug over a 30K mile period. Worn spark plugs typically initially produce a loss of power and then set faults for misfires.
A shortcut to finding out if you have a plug or coil problem is to identify the cylinder misfiring and swap the coil from the misfiring cylinder with a coil from a known good cylinder. If the misfire moves with the coil, you have a coil problem. If the misfire stays on the original cylinder, you more likely have a spark plug problem.
CEL – Misfire – Dead Cylinder
Typically associated with a CEL and rough running, the earlier V8 engine can experience a completely dead cylinder. Of course, replacing the plug and coil is the first step but, if the problem persists we’d recommend compression testing the cylinder involved.
Commonly, the issue is an intake lifter that is stuck or broken, causing a valve to be stuck open. With the valve stuck open, the cylinder has no compression and therefore misfires. If you’re lucky, this can be solved by replacing the lifter.
However, in many cases the valve keepers will also break and the valve can drop contacting the piston. This requires the removal of the head and valve replacement.
Symptoms: CEL – Power Loss – Lean Condition Fault Codes
An integral part of the emissions system, the PCV system is designed to extract oil from gases in the crankcase. The oil is recycled to the sump, while the gas is passed through the combustion path to be burnt and cleaned by the catalytic converters.
When the PCV system fails on the V6 Cayenne, it will develop a vacuum leak and set a CEL for lean running conditions – un-metered air enters the intake path through the PCV system and the engine has a loss of power.
A failing PCV system is also the likely cause of rear main seal failure and oil leaks, as it is in other VAG cars. Crankcase gas is not extracted well enough as the PCV fails. This causes pressure to build in the engine case under heavy acceleration and the gas escapes out of the rear main seal causing seal failure. This is commonly seen on all VAG V6 engines.
Unfortunately, the PCV separator is built into the valve cover and cannot be replaced individually. The repair requires the replacement of the whole valve cover assembly.
Symptoms: CEL – Rough Running – Timing Faults
The much talked about camshaft adjuster bolt problem generally affects vehicles produced between 2010 and 2012 model years. The problem lies in the aluminum bolts that secure the timing chain sprockets to the camshaft adjusters.
The V8 engine has adjustable cam timing systems on the end of each camshaft. The timing chain drives the adjuster, which varies the position and rotation of the cam based on engine performance demands. The adjuster is bolted to the end of the camshaft.
Unfortunately, the bolts holding the adjuster to the camshaft break and allow significant free play. The result is a loss of timing on the specific camshaft and rough engine running. This sets a check engine light and fault codes for multiple items including camshaft position sensor, misfires and cam to crank timing faults. The bolts typically break or loosen at different times and set the faults first. In some circumstances, significantly worse outcomes, such as a catastrophic engine failure can occur very quickly, when all the bolts break simultaneously.
We experienced a V8 running very badly and setting faults for camshaft position sensor, misfires etc. Further investigation revealed that the intake camshaft was not rotating at all and all the bolts on the adjuster had broken.
Porsche was required to recall 2010 through 2012 vehicles to correct this problem. If you are looking at a model in those production years, you should definitely check for evidence the recall work was completed. More information on the recall at http://www.camshaftadjusterrecall.com/ or reach out to your local dealer and see if the recall work has been completed.
Symptoms: Clunking or Banging Down Center of Car Under Acceleration
The Cayenne is infamous for a noisy drive shaft accompanied by clunking sounds on acceleration or when switching gears. This is usually caused by a failure in the driveshaft support bearing.
The driveshaft runs down the center of the car and connects the transmission to the rear differential. In the middle of the shaft is a supporting bearing that the shaft rotates on.
When the center support bearing fails, the shaft wobbles, vibrates and thumps during acceleration. You’d be hard pressed to find an early Cayenne that hasn’t experienced this problem or currently be somewhere close to experiencing it again. Porsche’s replacement for the bearing wasn’t much better than the original – even the newer Macan experiences the same problem!
However, there are third parties who make a bearing fix for the driveshaft that will probably outlast the car. The aftermarket solution does not require the driveshaft to be removed to complete the job and usually will save you money on the repair. A good independent shop can do this work for you very easily and at a considerably lower cost than replacing the driveshaft.
Symptoms: No Start, Start and Die, CEL Random Multiple Misfires
Fuel pump failure on the Cayenne is very common. Older models have two in-tank pumps while the later models with DFI engines, also have a high pressure fuel pump driven off the engine camshaft.
Low Pressure Fuel Pump Failure
Failure of the in-tank pumps is very common. Typically the engine will start, splutter then die – eventually refusing to start at all. This is caused by the pump overheating very quickly and shutting off. Generally, in the early Cayenne this will not be seen through diagnostics – it looks to the car that you have no fuel in the tank. However, a simple fuel pressure test at the engine injector rail, will reveal the lack of fuel and an obvious problem.
Porsche has updated both of the in-tank pumps a number of times and when having this issue, it makes sense to replace both the pumps and associated filter in a single job.
High Pressure Fuel Pump Failure
On the later engines with direct injection (DFI), the high pressure required to deliver fuel comes from a pump driven by the engine camshaft. A failure in the high pressure fuel pump has very similar symptoms to the failure of the in-tank pumps. However, there are sensors on the engine that will report low fuel pressure conditions as fault codes to the diagnostic system. Low pressure in the fuel system will usually begin as random multiple misfires and a loss of power under acceleration.
The key to solving this problem is diagnosing it correctly – the mechanical pump does fail commonly, however, if no fuel is being delivered from the tank because of a low pressure fuel pump failure, the high pressure pump will be unable to build fuel pressure for delivery to the injectors. This might look like a high pressure fuel pump problem when it isn’t! A good repair shop can accurately diagnose this for you.
Symptoms: HVAC Fan Stops Working, Single Speed Only or Noisy Operation
A common problem in the Porsche Cayenne is a condition where the climate control fan suddenly starts working intermittently, or only at one speed, or not at all. It may also become excessively noisy.
Blower Motor Regulator
The variation in the speed of the HVAC blower fan is controlled by the blower motor regulator. Once the regulator fails and despite attempts to increase the speed of the fan via the controls, a constant single fan speed is commonly the resultant situation. Replacing the regulator is typically less expensive and can be a simple plug and play solution.
Blower Motor Failure
When the HVAC blower fan has no speed at all or is noisy, it’s most likely that the blower motor itself may have failed. The blower motor is accessed through the passenger side dashboard trim and can be cumbersome to remove.
It makes sense to replace the fan and the regulator at the same time. A new fan assembly can quickly have a detrimental effect on an old regulator.
Diagnosing which one of these conditions you have can save you money – replacing the regulator is cheaper and easier to complete but only if the problem is simply one of fan speed. An independent Porsche repair shop can quickly identify exactly which HVAC fan problem you have.
Symptoms – Steering Faulty Message On Dash – Car Will Not Respond to Key
This happens when a convenience system becomes inconvenient. Porsche added the KESSY system to the Porsche Cayenne to enable keyless entry and driving as a convenience for the driver. Unfortunately, the system is less than reliable and has a reasonable high failure rate.
Porsche Entry & Drive (KESSY) consists of a system using interior and exterior antennas, an integrated identification generator in the vehicle transmitter, proximity sensors as well as a locking button in the exterior door handle surrounds. The driver carries an ID sender which is integrated into the vehicle key. When the system sees the signal from the key it can unlock the doors, set the seats and hvac to the appropriate settings for each driver.
Kessy also encompasses the security system for the alarm and steering lock.
Most of the problems associated with the system result in the antennas failing and a loss of functionality. Most people ignore this or don’t even realize it happened. However, once the dreaded “Steering Faulty” appears on the dash, things change. The steering wheel is now locked and the car is unresponsive to the key. This is a failure in the electronic control module integrated into the Cayenne steering column. The car is literally stuck where it is until you have it towed.
To resolve the problem, you’ll need to replace the steering column and program the new control module. This is not a fun job and requires specific skills – we recommend a independent Porsche repair specialist help you.
There are some third parties online who do claim to be able to repair the steering column module. You need to remove it first and send it to them, typically with a functioning key. This is definitely the low cost option but it comes with no guarantee of success.
Symptoms: Chassis System Failure Message, Uneven Ride Height, PASM Fault
This fault becomes evident on your Cayenne dashboard when a malfunction occurs in the air-ride suspension system. The system has a number of components, but generally, only one failure indicator. Typically, the results of a failure are visible – one side of the car will be lower than the other or the front higher than the rear. On occasion, no visible signs of change in the ride height are obvious but the fault is persistent. In colder climates, the fault can be sporadic initially, based on air temperature.
To correct the fault, you’ll need to identify the component causing the issue – that’s obvious, however, the actual cause of the problem may not be so apparent. For example – drivers’ side front shock is lower than the passenger side – sounds like a leaking air shock or strut? Maybe, but it could also be a ride height sensor, leaking hose, faulty valve block or bad electrical connector!
Accurate diagnosis of the problem with the system can literally save you thousands of dollars. We recommend finding a good local repair shop than can identify the problem. Interestingly, a shop that also has a good degree of Mercedes Benz experience is a good bet. Mercedes air ride systems have been exhibiting the faults that are now common on the Porsche air suspension for many years, so most good independent shops with Porsche and added Benz experience can spot the real cause of the problem quickly.
Components and Common Failures
The air compressor supplies the system with compressed air. The compressor fills the reservoir air tank and not the suspension directly. The compressor is designed to run in short bursts to top off the tank.
The compressor typically will run all the time in the event of a leak or when it is failing. Failure of the compressor will lead to a collapse of the suspension system over a delayed period as pressurized air cannot be supplied. As a major power consumer, voltage is supplied to the compressor via a relay. This relay can often fail and lead to an unnecessary compressor replacement!
The air supply tank is the least likely area of failure. This simply stores the compressed air to enable enough volume to be delivered quickly to correct the vehicle ride height. The tank supplies air to the system via the valve block – a hole in the line from the tank to the valve block will cause a system wide failure.
Compressed air is supplied to the valve block from the air tank. The valve block is an electro-mechanical device that routes pressurized air to the individual system components per instructions sent from the control module. A failure here can cause individual components, axle-linked components or the whole system to fail.
Air lines or hoses
The air hoses travel from the valve block to the individual system components. Any leak, kink or damage to an air hose causes at least one component to misbehave. Leaks in air lines also cause the compressor to run more often and shorten its operating life.
Front Air Shocks or Struts – Rear Air Spring
The air ride shock, strut or spring is filled or indeed emptied of compressed air via the air hose and valve block. Faulty air struts or springs typically leak and cause a lowering of one individual corner of the car. Two failing at the same time is unusual, so if you have a lower than normal ride height across one axle, do not assume leaking struts – see level sensors below. Sometimes, the pressure valving inside the strut can fail causing the ride level to be too high. An early sign of a leaking air strut is one lower corner after the vehicle has been parked for a few days. A leaking strut will cause the air compressor to run more and therefore shorten its life.
Each of the suspension components has an electrical connector. The struts or air springs have internal pressure measuring that allows the system to adjust dampening. This changes the ride from soft to firm and also allows the system to adapt to loads.
The electrical connectors can become corroded or greened in some circumstances. This causes the system to report malfunctions but typically does not affect ride height. Ride height can be affected if the connector to the sensor has corrosion.
Ride Height Level sensors
The ride height sensor is a small electro-mechanical component that connects the suspension to the body of the car. A small plastic arm translates vertical vehicle movement into rotational movement in the sensor. Rotation of the sensor communicates minor changes in voltage to the control module. Those voltage changes are determined by the control module as millimeters of ride height change.
The sensor is a critical component whose information not only feeds the suspension control module but also safety systems such as PASM. Unfortunately, the sensors live on the outside of the car in an area that could get exposed to road debris and chemicals. Failure of these sensitive components is inevitable.
Ride height sensor faults can be fun! A dead sensor is straightforward to diagnose – no signal. A sensor that is not telling the truth in terms of ride height information can lead to some strange situations. Because a ride height signal is still reaching the control module from a faulty sensor, action is taken based on that faulty information. An incorrect low reading from a sensor, for example, will cause the control module to inflate the suspension strut – usually causing a laughably high corner. Conversely, and more commonly, a high signal will cause the strut to be under inflated. This looks like a leak and is commonly mis-diagnosed.
Suspension Control Module
The suspension control module runs the whole system and communicates information to other vehicle systems. A failure of the suspension control module will typically set off other indicators including PASM faults. The control module is one of the least likely items in the system to fail. A typical failure will be a complete shutdown of the suspension. Control module failures rarely cause part system failure.
Switch failure is commonly overlooked. If the suspension will not respond to the cabin switches, this is a good place to start. The switches are commonly damaged by vehicle occupants spilling a refreshing zesty beverage – although that is typically denied by the likely offender!
Symptoms: ABS or PSM Warning Light – No Start
ABS or PSM failure can be serious. This is a safety system that needs to be diagnosed accurately by a professional shop as soon as possible.
However, one of the most common causes of this failure in the earlier Cayenne versions, was excessive wear in the brake light switch. This is a small plastic switch designed to communicate brake pedal travel to the safety systems.
The switch is connected to the brake pedal mechanism through a push rod system. Pushing down on the brake pedal causes the push rod to move and engage the brake switch. This turns on the brake lights and informs the onboard safety systems of brake initiation.
Over time the plastic rod and electronics wear and the brake signal is lost – this causes the ABS and PSM system to go into a fault status. It can also cause a failure of brake lights and a no start situation. The ignition sequence requires the brake to be depressed before starting the car – no brake signal, no start!
Replacing the switch is pretty straight forward and inexpensive. Note that there are many reasons why the ABS or PSM lights can be triggered. Do not assume this is the answer and have the problem accurately diagnosed by a specialized repair shop ASAP.
Symptoms: Airbag Light Flashes or Stays On and Goes Off Randomly
Many Cayenne drivers have noted that their airbag fault light flashes randomly. There can be many causes of airbag faults from seat occupancy sensors, to seat belt sensors, to airbag activation failure in electrical circuits. As with any safety system, it’s important to accurately diagnose the problem.
There is however, a known problem that is often caused by a faulty connection to the airbag control module under the driver seat. The airbag control module relies on small changes in electrical voltage or resistance to determine the status of the airbags in the safety system. Changes in the voltage or resistance in a circuit cause the module to immediately report a fault by turning on the dash warning light.
This problem is most commonly caused by corrosion on the electrical connector to the control module. Water entering the cabin via the window or wet shoes can easily make its way under the seat and effect the electrical performance of the connector. Check to see if water has damaged any of the electrical pins and plugs. In many cases, the connector and control module will need to be replaced.
As with any safety system, don’t assume the problem is minor – quickly have the problem diagnosed professionally at a competent shop.
Symptoms: Brake Booster Fault Dash Message, Harder Brake Pedal
The Porsche Cayenne features a complex engine vacuum system that is driven by a pump. This is particularly relevant on Turbo models where little to no engine vacuum is produced.
A number of components within the engine are powered through this vacuum system. The most common fault set through a failure in this system is that of the brake booster fault.
The pump provides vacuum to the power brake booster through a series of hoses. The level of vacuum is monitored through a sensor and a drop in vacuum can cause the sensor to report the fault to the dashboard. Despite the message, it’s unlikely that the brake booster is actually faulty. Typically the problem lies in a lack of vacuum to the booster as a result of a crack in one of the vacuum lines.
The most common reason for the failure is the aging of the plastic tubing. Over time, the hard plastic tubing heats and cools rapidly. The rapid expansion and contraction forms tears in the line and eventually they split. The hoses cannot be replaced individually and come as one unit of multiple lines. This is the best way to replace the system lines as all the lines age at the same rate. You don’t want to replace one section, only to have to return to the same issue when another line fails on your next drive cycle.
Assuming all the lines are in good shape and hold vacuum, then the problem may well lie with either the vacuum pump itself or the sensor. These are straight forward to replace and are a common wear item. A complete lack of vacuum should be fairly obvious to diagnose.
Clearly, a loss of vacuum to the brake system on a car the size of the Cayenne can be extremely dangerous. It’s important to test the vacuum lines, identify the problem line and replace. Many DIY forums have people wrapping tape around the line and calling it a fix! Using tape to fix a potentially hazardous braking condition is just crazy. Replace the line or have a independent repair shop do it for you.