It needs to be reprogrammed
PCM REPLACEMENT TIPS:
Replacing a PCM is essentially a matter of swapping boxes. Accessibility can be a problem on some vehicles because the PCM is often buried under or behind other components in the instrument panel, climate control system or console. Some are located under a seat and require removing the seat.
Regardless of the PCM's location, though, one thing you should do prior to removing the old PCM and installing the replacement PCM is disconnect the battery.
Once the PCM has been installed and reconnected, the battery can be reconnected, too. But the job is not done yet. Many PCMs have to undergo a "relearning" procedure after they have been installed or if they have been disconnected from the battery. On some newer vehicles, a scan tool may be required to reprogram the PCM and to reset the anti-theft system.
On some applications, there may be a specific relearn procedure for establishing the base idle speed and other operating parameters. On others, it may be necessary to take the vehicle for a short test drive so the computer can adjust itself. The exact requirements will be spelled out in the vehicle service manual. The best advice here is to test drive the vehicle after the powertrain control module has been installed. A short drive cycle that includes going over 35 mph will usually reset most PCMs so they will operate properly.
The powertrain control module will also continue to learn and make small adjustments to the fuel mixture and other functions over time as the vehicle accumulates miles. If the PCM also controls the transmission, it may take awhile to relearn the driver's habits so the transmission may not shift exactly the same as before until this occurs.
Finally, if the Malfunction Indicator Lamp (MIL) or Check Engine light comes back on after the PCM has been replaced, it means there is still a problem with the vehicle. The fault is probably NOT the PCM, unless the fault code is for an internal PCM fault. The presence of fault codes means additional diagnosis is required to identify and repair the fault. And until the real problem is found and fixed, the PCM may not function normally.
If the engine control system is not going into closed loop, chances are the coolant sensor or oxygen sensor may not be working properly. If spark timing seems to be over advanced or retarded, the problem may be a faulty MAP sensor, misadjusted throttle position sensor or overly sensitive knock sensor. And if nothing seems to work right, low charging voltage due to a weak alternator or poor battery connections may be the fault.
Remember, a powertrain control module needs all its sensor inputs, proper battery voltage, a good ground and the ability to send out control signals to function normally.
Saturday, December 27th, 2008 AT 4:52 PM