GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Geo 🢒 1996 🢒 Tracker - 2WD 🢒 Transmission/Transaxle 🢒 Automatic Transmission - 4 Speed-M41 🢒 On-Board Diagnostic System Check

Refer to Automatic Transmission Controls Schematics .

Description

The OBD system check is an organized approach to identifying a problem created by an electronic transmission control system malfunction. The OBD system check is the starting point for any transmission diagnosis because it directs the service technician to the next logical step in diagnosing the concern. Understanding the table and using it correctly will reduce diagnostic time and prevent the replacement of good parts. DO NOT perform this check if a transmission concern is not present.

Diagnostic Aids

An intermittent malfunction may be caused by a fault in a transmission control system electrical circuit. Inspect the wiring harness and components for any of the following conditions:

    • Backed out terminals
    • Improper mating of terminals
    • Broken electrical connector locks
    • Improperly formed or damaged terminals
    • Faulty terminal to wire connections
    • Physical damage to the wiring harness
    • A broken wire inside the insulation
    • Corrosion of electrical connections, splices, or terminals

Test Description

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

  1. The OBD system check should not be performed unless one of the concerns noted is present. Failure to follow this procedure could lead to misdiagnosis of the system.

    2.

  2. The MIL should be on steady with the key on and the engine off.

    3.

  3. This step checks if the TCM and the scan tool can communicate (serial data).

    4.

  4. This step checks if the vehicle will start.

    5.

  5. Before proceeding to the applicable DTC table consider all of the items below.

    Check for related service bulletins.

    If the scan tool is unable to record DTC information then record the DTC information on paper.

    If multiple DTCs are stored, refer to the DTC tables using the following priority:

    6. 1. TCM error DTCs
    2. System voltage DTCs
    3. Component level DTCs
    4. System level DTCs.

  6. This step detects a MIL circuit shorted to ground.

    7.

  7. Before proceeding to Symptoms or Diagnostic Information and Procedures, check for related service bulletins. The diagnostic tables in this section are designed for use with a properly functioning and updated scan tool. If a faulty scan tool is suspected connect it to another vehicle to verify operation. Serial data communications must be corrected before beginning any other diagnostic procedure. OBD serial data may not transmit if system voltage is below 9.0 volts or above 16.0 volts. DO NOT clear DTCs unless directed by a diagnostic procedure. Clearing DTCs will also clear valuable Freeze Frame/Failure Record data.

Step

Action

Value(s)

Yes

No

1

Important: 

   • Check for Service Bulletins
   • DO NOT Turn OFF the ignition during this diagnostic unless instructed to do so.
   • Do not clear the DTCs unless instructed to do so.

Check for one or more of the following conditions:

    • The malfunction indicator lamp (MIL) illuminates with the engine running.
    • A customer concern of transmission performance
    • Suspected fault in a TCM controlled component or system

Did any of the above conditions apply?

--

Go to Step 2

System OK

2

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

Is the MIL illuminated?

--

Go to Step 3

Go to Malfunction Indicator Lamp Inoperative in Engine Controls

3

  1. Turn OFF the ignition.
  2. Install a scan tool.
  3. Turn ON the ignition, leaving the engine OFF.

Does the scan tool display any TCM data?

--

Go to Step 4

Go to Data Link Connector Diagnosis in Engine Controls

4

Start the engine.

Did the engine start and run?

--

Go to Step 5

Go to Engine Cranks But Does Not Rune in Engine Controls

5

Observe the DTC information. If any DTCs are set, save the DTC and Freeze Frame/Failure Record information.

Were any DTCs set?

--

Go to Step 5

Go to Step 6

6

Is the MIL ON with no DTCs set?

--

Go to Malfunction Indicator Lamp Always On in Engine Controls

Go to Step 7

7

Compare the scan tool data display with the data values that should be present when the transmission components are requested.

Are the displayed values normal or showing the typical display data?

--

Go to Symptoms

Go to the Diagnostic Aids of the DTCs related to the component