Fault Codes and Over-Revs – All Chassis
Before buying any car, it is essential to know when the last time the system fault codes were cleared and to check the status of the emission monitors. It’s not difficult for a seller to clear the faults just before you arrive for a test drive. Clearing the engine faults also resets the emissions system to a state of “not ready.” Emission readiness tests often occur over multiple drive cycles. So, after a reset, faults may not return for a significant number of miles. Again, this is easy for a competent shop to check or indeed the DIYer using a handheld scanner.
How hard has the car been driven? Taking the engine to the red line for RPM is a good thing, but going over the red line obviously can cause damage. A gear change at red line will actually cause the revs to increase slightly momentarily – nothing bad here. But, if you select the wrong gear, the engine revs to go way over the red line. This is the famous “miss-shift” that has caused many engine explosions.
Thankfully, Porsche engine management records many things – one of the most significant is an over-rev situation. Data is permanently stored within the ECU showing running hours and when engine events have occurred. There are six levels of over-revs recorded, ranging from the engine being red-lined through to what would be a potentially catastrophically high RPM event. Events in the first category suggests the car has been properly exercised, but events in the higher categories could be hiding a potential life shortening engine situation.
Many Porsche owners like to go to track days. On the track, gear changes will occur right around the rpm maximum red line. These events will be recorded if they reach the lower levels of the over rev counter. Multiple recorded events in the lower over-rev categories could be a sign of how much track time the car has experienced.