For 1990-2009 cars

### Diagnosis

Use a scan tool in order to read DTCs.

To clear the DTCs from memory:

• | Using a scan tool is recommended.

| OR

• | Turn the ignition off for at least 10 seconds, then disconnect the negative battery cable for 30 seconds.

Notice: Clearing the PCM DTC memory by disconnecting the battery will clear all PCM memories. Since some operations (particularly IAC valve idle control) are learned, it may be necessary to partially depress the accelerator pedal when re-starting the engine after PCM memory is cleared. It may also be necessary to release the accelerator pedal very slowly when first returning to idle, to prevent a stall. This will allow the PCM to re-learn IAC valve position. Learned operations may be restored by normal driving.

Because the powertrain control module (PCM) can have a malfunction which may affect only one circuit, the following diagnostic procedures in this section will determine which circuit has a problem and where the problems.

If replacement of the PCM does not correct the problem, one of the following may be the reason:

• | There is a problem with the PCM terminal connections. The diagnostic table will say PCM electrical connections or PCM. The terminals may have to be removed from the connector in order to inspect the terminals properly.

• | The PCM, or EEPROM calibration, is not correct for the application. The incorrect components or calibration may cause a malfunction and may or may not set a DTC.

• | The problem is intermittent. This means that the problem is not present at the time the system is being tested. In this case, refer to Symptoms and make a careful physical inspection of all portions of the system involved.

• | A shorted solenoid, relay coil, or harness. Solenoids and relays are turned on and off by the PCM using internal electronic switches called drivers. Each driver is part of a group of 7 called an output driver module or group of 4 called a quad-driver module. The drivers switch the ground side of a solenoid or relay circuit which is fed by a connection to the battery voltage. A shorted or low resistance solenoid or relay, or a shorted harness, can allow too much current to flow through a driver. This will not permanently damage a PCM, as the driver will limit the current. However, a circuit which tends to allow too much current into the driver will probably cause the solenoid or relay to become inoperative, and can be diagnosed in Air Conditioning (A/C) Compressor Control Circuit Diagnosis for the A/C relay, Electric Cooling Fan Diagnosis for the cooling fan relay, and Powertrain Control Module Outputs Diagnosis for the output driver module outputs.

• | The EEPROM may be malfunctioning. Although the EEPROM will rarely fail, the EEPROM operates as part of the PCM. Therefore, the EEPROM could be the cause of the problem. A DTC will set if the EEPROM is malfunctioning. Follow any DTC tables for any DTCs that may set.

• | The replacement PCM may be malfunctioning. After the PCM is replaced, the system should be re-tested for proper operation. Refer to Powertrain On Board Diagnostic (OBD) System Check . If a diagnostic table again indicates the PCM is the problem, substitute a known good PCM. Although this is a rare condition, it is possible.

### Powertrain Control Module (PCM)

A faulty PCM will be determined in the diagnostic tables. Before replacing the PCM, a re-programming procedure should not be attempted unless instructed. If the re-programming is unsuccessful a DTC P0602 will set.

An incorrect or malfunctioning EEPROM, which is part of the PCM, will set a DTC P0601. Before replacing the PCM, a re-programming procedure should not be attempted unless instructed. If the re-programming is unsuccessful a DTC P0602 will set.