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Modern Automotive Diagnostics

Tech Notes from Tony Callas

(courtesy of Callas Rennsport)

Automotive repair, like many other professions, has changed drastically over the last 15 years. It has gone from a completely mechanical hands-on diagnosis and repair, to an almost hands-off research based process.

Too many automotive repair facilities will erase the fault code(s) — “just turn the warning light off”, at the customer’s request. In almost all situations, this is the wrong approach to a proper overall repair. By turning off the warning light (ie: erasing the fault codes), they are removing the history — valuable data and detailed information that can be utilized for properly diagnosing the vehicle.

Fault codes should never be erased unless the issue or fault is repaired.

From 1996 on, all vehicles sold in the USA have what is known as OBD-II (On Board Diagnostics II). OBD-II is the gatekeeper of the engine management system, which oversees all operating parameters that effect engine tailpipe emissions (including monitoring the evaporative emissions system - ie: fuel tank vapor containment and processing). OBD-II constantly monitors tailpipe emissions via the oxygen (emissions) sensors in the exhaust stream.

If tailpipe emissions reach or exceed a predetermined threshold, the low emission standards are in jeopardy. If this happens, the computer will set a fault code and illuminate the check engine warning light (CEL).

Many other systems on the car also monitor their own operation. Some examples are the MRS (multiple restraint system — air bags), TPMS (tire pressure monitoring sensors) etcetera. The same diagnosis procedures need to be followed regardless of the system in question.

Here is my approach to modern Porsche diagnosis:

  1. Confirm the customer complaint(s) and note down all issues. Then test drive vehicle if applicable.
  2. Interrogate all control units with a factory (preferred) diagnostic tool (eg: the Porsche PIWIS tester.
  3. Print out the fault codes and relevant data.
  4. Check the factory technical service bulletins for recommended repair possibilities or upgrades. This includes reprogramming, recoding and software upgrades, and is especially true on cars produced from 1996 on.
  5. The computer data, factory information and the vehicle’s symptoms, plus the technician’s experience and training will provide the direction to the proper diagnosis.
  6. Once the repair is performed, the process is not yet completed. Now the repair must be confirmed by utilizing the factory diagnostic tool so the technician can identify that the problem(s) are no longer present. Only at this point can it be considered that the repairs are completed.