The onboard computer, or Powertrain Control Module (PCM),is the brains of the engine control system, so when the brain is not functioning correctly neither is the engine or anything else that the microprocessor
controls - which may include the charging system, transmission, various emission controls and communications with other onboard control modules. Once a diagnosis has been made (and we emphasize the word diagnosis), then and only then should the PCM be replaced.
P0600....Serial Communication Link
P0601....Internal Control Module Memory Check Sum Error
P0602....Control Module Programming Error
P0603....Internal Control Module Keep Alive Memory (KAM) Error
P0604....Internal Control Module Random Access Memory
P0605....Internal Control Module Read Only Memory (ROM) Error
P0607....Control Module Performance
P0608....Control Module VSS Output 'A'
P0609....Control Module VSS Output 'B'
P0610....Control Module Vehicle Options Error
If you see any of these codes when diagnosing the vehicle with a code reader or scan tool
, it may mean the PCM has failed and must be replaced. Additional diagnostic tests will usually be necessary to confirm the problem is really the powertrain control module and NOT something else. Refer to the OEM diagnostic charts for what these tests are. Usually it involves checking certain inputs to the PCM to see if it outputs the correct response. No response or an incorrect response usually means the PCM is defective and needs to be replaced.
All too often, technicians tend to blame that which they understand least. If an engine is not running right and the cause is not obvious, they may blame the computer. Throwing parts at a problem in an attempt to solve it may be good for the parts business, but when a customer brings a PCM back because it failed to fix their problem, nobody wins. Warranty returns on complicated and expensive components like powertrain control modules are an ongoing problem that costs everyone money.
UNNECESSARY POWERTRAIN CONTROL MODULE RETURNS.
Over 50 percent of PCMs that are returned under warranty (either because the PCM failed to fix a performance problem or because the engine did not run properly after it was installed) have nothing wrong with them! So it is obvious a lot of people are swapping computers to see if a different PCM will fix their problem.
The trouble with returns is if the PCM has been on the car, you have no way of knowing if it is still "good" or not. Somebody may have crossed up some wires, zapped the PCM with too much voltage
or who knows what? The computer needs to be tested and verified before it can go back on the shelf and be sold to somebody else.
Unfortunately, there is no easy way of doing that in a parts store. The PCM has to be hooked up to a sophisticated simulator that exercises all of the computer's input and output circuits to make sure it works correctly - which means the PCM has to go back to the supplier, be retested, and if no fault is found, repackaged and put back into stock.
Be warned, though, that many parts stores have a policy of "no returns or refunds on electronic components."