Diagnosis
Use a scan tool in order to read DTCs.
To clear the DTCs from memory:
| • | Using a scan tool is recommended. |
| • | 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.
