GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2000 🢒 LeSabre 🢒 Engine 🢒 Engine Electrical 🢒 Powertrain On Board Diagnostic (OBD) System Check

Refer to Engine Controls Schematics for a wiring diagram.

Circuit Description

The Powertrain On-Board Diagnostic 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 PCM and the engine grounds for being clean and tight. The Powertrain On-Board Diagnostic System Check is an organized approach to identifying a problem created by an electronic engine control system malfunction.

Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed-through wire insulation, or 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, and a 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 / 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 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 in order 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 DTCs which are diagnosed in 4T65-E Automatic Transaxle Diagnosis. Reviev the 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, including the switches, the sensor range and performance, sensor high voltage, sensor low voltage, ODMs, etc.
    • System level DTCs, including fuel trim, misfire, EGR flow, the TWC system, the idle control system, and the 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

Value(s)

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 malfunction indicator lamp (MIL).

Is the MIL illuminated?

--

Go to Step 2

Go to Malfunction Indicator Lamp (MIL) Inoperative

2

  1. Install a scan tool.
  2. Attempt to display PCM data.

Does the scan tool display 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 that any DTCs have set, record the Freeze Frame and Failure Records.

Use the scan tool in order to display the DTCs.

Does the scan tool indicate that any DTCs have set?

--

Go to the applicable DTC

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 Component System Checks