Century V6-173 2.8L VIN W FI (1987)
Engine Control Module: Component Tests and General Diagnostics
ECM Diagnosis
READING CODES
To read the codes, use a "Scan" tool, or ground the diagnostic terminal, with the engine not running and the ignition "ON." The "Service Engine
Soon" light will flash Code 12 three times and then flash each code stored in memory three times. All codes stored in memory would have been
read when Code 12 was flashed again. No new codes can be stored when in the diagnostics mode (diagnostics lead grounded). This eliminates
confusion while the system is being worked on.
Electronic Control Module (ECM)
A faulty Electronic Control Module (ECM) will be determined in the diagnostic charts or by a Code 55.
MEM-CAL
An incorrect or faulty Mem-Cal, which is part of the ECM, may set a Code 41 or 51.
CLEARING CODES
^
Ignition "OFF."
^
Disconnect ECM fuse in holder for 30 seconds.
^
Since the ECM can have a failure which may affect only one circuit, following the diagnostic procedures in this section will determine which
circuit has a problem and where it is.
If a diagnostic chart indicates that the ECM connections or ECM is the cause of a problem, and the ECM is replaced, but does not correct the
problem, one of the following may be the reason:
Problem with the ECM terminal connections.
The diagnostic chart will say ECM connections or ECM. The terminals may have to be removed from the connector in order to check them
properly.
ECM, or Mem-Cal is not correct for the application.
The incorrect components may cause a malfunction and may or may not set a code.
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" portion of the manual
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 ECM, using internal electronic switches called "drivers." Each driver is part of a
group of four called "quad-drivers." Failure of one driver can damage any other driver in the set.
^
A shorted solenoid, relay coil, or harness in a GMP4 computer will not damage the ECM but will cause the component to be inoperative.
^
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.
Mem-Cal may be faulty.
Although these rarely fail, it operates as part of the ECM. Therefore, it could be the cause of the problem. Substitute a known good Mem-Cal.
Replacement ECM may be faulty.
After the ECM is replaced, the system should be rechecked for proper operation. If the diagnostic chart again indicates the ECM is the
problem, substitute a known good ECM. Although this is a rare condition, it could happen.
