Tahoe 4WD V8-393 6.5L DSL Turbo VIN S (1995)
Engine Control Module: Component Tests and General Diagnostics
Since the Powertrain Control Module (PCM) can have a failure which may affect only one circuit, following the diagnostic procedures in this
section can reliably tell when a failure has occurred in the PCM. Also, a Diagnostic Trouble Code (DTC) 54 indicates a failure of the PCM.
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 Programmable Read Only Memory (PROM) is not correct for the application. The incorrect PCM or PROM 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 Diagnosis
by Symptom and make a careful physical inspection of all portions of the system involved. See: Computers and Control Systems/Testing and
Inspection
^
Shorted solenoid. relay coil. or harness. - Solenoids and relays are turned "ON" and "OFF" by the PCM, using internal electronic switches
called "Drivers."
A shorted solenoid, relay coil, or harness will not damage the PCM, but will cause the circuit and controlled component to be inoperative. When
the circuit fault is not present or has been repaired, the driver will again operate in a normal manner due to it's fault protected design. If a fault has
been repaired in a circuit controlled by a driver, the original PCM should be reinstalled and the circuit checked for proper operation. PCM
replacement will not be necessary if the repair circuit or component now operates correctly.
J 34636 or BT-8405 testers or equivalent provide a fast, accurate means of checking for a shorted coil or a short to battery voltage.
^
The PROM may be faulty. - Although the PROM rarely fails, it operates as part of the PCM. Therefore, it could be the cause of the problem.
Substitute a known good PROM.
^
The replacement PCM may be faulty. After the PCM is replaced, the system should be rechecked for proper operation. If the diagnostic chart
again indicates the PCM is the problem, substitute a known good PCM. Although this is a rare condition, it could happen.
PROM
A PROM that has failed or was installed improperly will generally set a DTC 51.
