Engine Control Module: Testing and Inspection

ECM DIAGNOSIS
To display the ECM DTC, use a Tech 1 or ground the diagnostic "test" terminal with the engine not running and the ignition "ON." the Malfunction Indicator Lamp (Service Engine Soon) will flash DTC 12 three times and then flash each DTC stored in memory three times. All DTCs stored in memory would have been read when DTC 12 was flashed again. No new DTCs can be stored when in the diagnostics mode (diagnostics lead grounded). This eliminates confusion while the system is being worked on.

To clear the DTCs from memory use a Tech 1 scan tool or:

- Ignition "OFF."
- Remove ECM maxifuse located in maxifuse block #1 near the battery, for 30 seconds.

Since the ECM can have a failure which may affect only one circuit, following the diagnostic procedures in this 5ecti0n 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:

There is a problem with the ECM terminal
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.

The ECM or PROM is not correct for the application.
The incorrect components 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 visual / 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."

A shorted solenoid, relay coil, or harness will not damage the ECM, but will cause the circuit and controlled component to be inoperative. When the circuit fault is not present or has been repaired, the "quad-drivers" 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 "quad-driver," the original ECM should be reinstalled and the circuit checked for proper operation. ECM replacement will not be necessary if the repaired circuit or component now operates correctly.

J 34636 or BT-8405 testers provide a fast, accurate means of checking for a shorted coil or a short to battery voltage.

The PROM 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 PROM.

The 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.

PROM
An incorrect or faulty PROM, which is part of the ECM, may set a DTC 41 or DTC 51. Also, make sure the PROM is fully seated and latched in the socket.