Powertrain Control Module Diagnosis. Chevrolet Beretta 1996

For 1990-2009 cars

### Diagnosis

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.

Use a scan tool in order to read the DTCs. .

In order to clear the DTCs from memory:

• | Use a scan tool (recommended).

| Or

• | Turn the ignition OFF for at least 10 seconds,

• | Disconnect the negative battery cable for 30 seconds (clears I/M Ready status flags).

Because the Powertrain Control Module (PCM) can have a fault which may affect only one circuit, the following diagnostic procedures in this section will determine which circuit has a problem and where it is.

If a diagnostic table indicates that the PCM connections or PCM is the cause of a problem, and the PCM is replaced, but 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 connections or PCM. The terminals may have to be removed from the connector in order to check them 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 checked. In this case, refer to the Intermittent Conditions and make a careful physical inspection of all portions of the system involved.

• | 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 seven called an output driver module or group of four called a quad-driver module. The drivers switch the ground side of a solenoid or relay circuit which is fed by connection to 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-6SU PCM, as the driver will limit 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 Clutch Control Diagnosis for the A/C relay, Electric Cooling Fan Diagnosis for the cooling fan relay, and Powertrain Control Module Outputs Diagnosis for output driver module outputs.

| J 34636 testers provide a fast, accurate means of checking for a shorted solenoid or relay coil or a short to battery voltage.

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

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

### Powertrain Control Module (PCM)

A faulty powertrain control module (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.