Diagnostic Circuit Check - California Emissions (GEN-II S)

Diagnostic Circuit Check:

Computer Wiring:

CIRCUIT OPERATION
The on-board diagnostic system check is an organized approach to identifying a problem created by an electronic engine control system malfunction. It must be the starting point for any driveability complaint diagnosis, because it directs the service technician to the next logical step in diagnosing the complaint. Understanding the chart and using it correctly will reduce diagnostic time and prevent the unnecessary replacement of good parts.


TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. This step is a check for the proper operation of the Malfunction Indicator Lamp (MIL) Service Engine Soon." When the ignition is turned "ON" the MIL should come "ON" and go "OFF" in approximately 3 seconds.

2. This test checks the ability of the ECM to control the MIL. With the DLC grounded the MIL should come "ON" steady.

3. Although the ECM is powered up, a "Cranks But Will Not Run" symptom could exist because of an ECM or system problem.

CAUTION: This vehicle is equipped with an Engine Control Module (ECM) utilizing an Erasable Programmable Read Only Memory (EPROM). When diagnostics call for replacement of the ECM, the new ECM must be programmed. Refer to "ECM Replacement and Programming Procedures".


4. This step will isolate if the customer complaint is a MIL or a driveability problem with no MIL. Refer to ECM diagnostic trouble codes for a list of valid DTC(s). An invalid DTC may be the result of a faulty scan tool, calibration or ECM.

5. Comparison of actual control system data with the typical values is a quick check to determine if any parameter is not within limits. Keep in mind that a base engine problem (i.e. advanced cam timing) may substantially alter sensor values.