Cavalier/Z24 L4-138 2.3L DOHC VIN D MFI (1995)
Engine Control Module: Initial Inspection and Diagnostic Overview
A faulty PCM will be determined in the diagnostic charts. Before replacing the PCM, a re-programming procedure should be attempted. If the
re-programming is unsuccessful a DTC P0602 will set.
SCAN TOOL TESTING
To read DTCs, use a scan tool.
To clear the DTC from memory:
-Ignition "OFF" for at least 10 seconds.
-Disconnect the negative battery cable for 30 seconds.
-Or, use a scan tool.
NOTE: 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.
DEFECTIVE CIRCUITS
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 chart 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 chart 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 program is not correct for the application.
The incorrect components or program 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 Symptoms, Section 6E3-B portion of
this section 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" (0DM) or group of four called a "Quad-Driver Module" (QDM). 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 0DM or QDM. This will not permanently damage a PCM-6SU PCM, as the ODM/QDM will limit current.
However, a circuit which tends to allow too much current into the ODM/QDM will probably cause the solenoid or relay to become inoperative. J
34636 or BT-805 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. Re-program the PCM. A DTC will set if
the EEPROM is faulty. Follow any DTC charts for any DTCs that may set.
EEPROM
An incorrect or faulty EEPROM, which is part of the PCM, should set a DTC P0601. Before replacing the PCM, a re-programming procedure
should be attempted. If the re-programming is unsuccessful a DTC P0602 will set.
