Diagnosis
To read DTCs, use a scan tool.
To clear DTCs from memory:
| • | Use a scan tool (recommended). |
| • | Ignition OFF for at least 10 seconds, |
| • | Disconnect the negative battery cable for 30 seconds (clears
status flags). |
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 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 Symptoms
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, 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 Control Circuit 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. |
| • | The EEPROM may be malfunctioning. 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 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-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.
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.
