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For 1990-2009 cars only
Makes 🢒 Buick 🢒 2000 🢒 Regal (China) 🢒 Body and Accessories 🢒 Instrument Panel, Gauges, and Console 🢒 Powertrain On Board Diagnostic (OBD) System Check

Circuit Description

The Powertrain On-Board Diagnostic (OBD) System Check must be the starting point for any driveability complaint diagnosis. Before using this procedure, you should perform a careful visual and physical check of the Powertrain Control Module (PCM) and engine grounds for being clean and tight. The Powertrain On-Board Diagnostic (OBD) System Check is an organized approach to identifying a problem created by an electronic engine control system malfunction.

MIL Operation

The malfunction indicator lamp (MIL) is located on the instrument panel (CHECK ENGINE) or (SERVICE ENGINE SOON). The MIL performs the following functions:

    • It informs the driver that a problem has occurred and that the vehicle should be taken for service as soon as possible.
    • As a system check, the MIL will illuminate with the ignition switch ON and the engine not running. when the engine is started, the MIL will turn OFF. If the MIL remains ON, the self-diagnostic system has detected a problem. If the problem goes away, the MIL will turn OFF in most cases, but a diagnostic trouble code will remain stored.
    • If the MIL is illuminated, then the engine stalls, the MIL will remain Illuminated so long as the ignition switch is ON.
    • If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, then ON.

Perform the Powertrain On-Board Diagnostic (OBD) System Check first, when the following conditions are present:

    • When the MIL does not turn ON when the ignition switch is turned to the RUN position.
    • When the MIL remains ON while the engine is running.
    • When you suspect a driveability problem.

Diagnostic Aids

An intermittent may be caused by:

    • A poor connection
    • Rubbed through wire insulation
    • A wire broken inside the insulation

Check for poor connections or a damaged harness.

Inspect the PCM harness and connectors for:

    • Improper mating
    • Broken locks
    • Improperly formed or damaged terminals
    • Poor terminal to wire connection
    • Damaged harness

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. The MIL should be ON steady with the key ON and the engine OFF. If not, the No Malfunction Indicator Lamp table should be used to isolate the malfunction.

    2.

  2. This test ensures that the PCM is capable of transmitting Class 2 serial data to the data link connector (DLC) and that the Class 2 data circuit is not open or shorted. If a problem is encountered and a malfunctioning scan tool is suspected, try the scan tool on another vehicle to verify operation. If a DLC problem exists, the DLC diagnosis table should be used to diagnose the condition.

    3.

  3. If the engine will not start, the Engine Cranks But Will Not Run table should be used to diagnose the condition.

    4.

  4. The scan tool may display diagnostic trouble codes (DTCs) which are diagnosed in 4T65-E Automatic Transaxle Diagnosis. Refer to DTC List for a complete list of DTCs supported by this vehicle application. If multiple DTCs are stored, diagnose each DTC according the following priority:

    5. • PCM Error DTCs
    • System Voltage DTCs
    • Component Level DTCs (Switches, sensor range/performance, sensor high voltage, sensor low voltage, ODMs, etc....)
    • System level DTCs (Fuel trim, Misfire, EGR flow, TWC System, Idle Control System, HO2S Response or HO2S Transition Time Ratio)

  5. A scan tool parameter which is not within the typical range may help to isolate the area which is causing the problem.

Powertrain On--Board Diagnostic System Check

Step

Action

Values

Yes

No

1

Important: 

   • Check for applicable service bulletins before proceeding with the diagnosis.
   • Do not turn OFF the ignition when performing this diagnostic table.
   • Do not perform this test if no driveability condition exists.
   • Unless instructed, do not clear any DTCs.

  1. Turn ON the ignition, with the engine OFF.
  2. Observe the MIL.

Is the MIL illuminated?

--

Go to Step 2

Go to Malfunction Indicator Lamp (MIL) Inoperative

2

  1. Turn OFF the ignition.
  2. Install a scan tool.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, attempt to display the PCM data.

Does the scan tool display the PCM data?

--

Go to Step 3

Go to Data Link Connector Diagnosis

3

Attempt to start the engine.

Did the engine crank?

--

Go to Step 4

Go to Starter Inhibit Relay Circuit Diagnosis

4

Did the engine start and continue to run?

--

Go to Step 5

Go to Engine Cranks but Does Not Run

5

Important: If the scan tool indicates any DTCs set, record the Freeze Frame/Failure Records.

Use the scan tool in order to display (DTCs).

Does the scan tool indicate any DTCs set?

--

Go to the applicable DTC table

Go to Step 6

6

With a scan tool, compare the PCM data to the Scan Tool Data List .

Does the scan tool indicate PCM values equal to or within the typical values?

--

System OK

Go to Symptoms