GM Service Manual Online
For 1990-2009 cars only

Circuit Description

Ignition voltage is supplied directly to the malfunction indicator lamp (MIL). The powertrain control module (PCM) controls the lamp by grounding the control circuit via an internal switch called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line which is monitored by the PCM. When the PCM is commanding a component ON, the voltage of the control circuit should be low, near 0 volts. When the PCM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be high, near battery voltage. If the fault detection circuit senses a voltage other than what is expected, the fault line status will change causing the diagnostic trouble code (DTC) to set.

Conditions for Running the DTC

    • The engine speed is more than 400 RPM.
    • The ignition voltage is between 6-18 volts.

Conditions for Setting the DTC

    • The PCM detects that the commanded state of the driver and the actual state of the control circuit do not match.
    • The conditions are present for a minimum of 5 seconds.

Action Taken When the DTC Sets

    • The PCM stores DTC P0650 in memory on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The PCM does not command the MIL ON.
    • The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the DTC

    • A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
    • A history DTC will clear after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
    • Use a scan tool in order to clear the DTC.

Diagnostic Aids

Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

    • If the ignition feed circuit is suspected of being open, inspect for other lamps on that circuit not illuminating. An open fuse causes the entire cluster to be inoperative. Also, if the fuse is open, transmission DTCs set.
    • Using Freeze Frame/Failure Records data may aid in locating an intermittent condition. If the DTC cannot be duplicated, the information included in the Freeze Frame/Failure Records data can be useful in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also be used to determine how many ignition cycles the diagnostic reported a pass or a fail. Operate vehicle within the same Freeze Frame conditions, such as RPM, load, vehicle speed, temperature etc., that were noted. This will isolate when the DTC failed. For an intermittent, refer to Intermittent Conditions .

Test Description

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

  1. This step tests for a short to ground in the MIL control circuit. With the PCM disconnected and the ignition ON the MIL should be OFF.

  2. This step tests for a short to voltage on the MIL control circuit. With the fuse removed there should be no voltage on the MIL control circuit.

  3. This vehicle is equipped with a PCM that utilizes an electrically erasable programmable read only memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.

Step

Action

Value(s)

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

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Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Verify whether the instrument panel (IP) is operational. If the IP is completely inoperative, refer to Diagnostic System Check - Instrument Cluster in Instrument Panel, Gauges and Console.
  2. Verify whether the MIL turns ON and OFF when commanded.
  3. Turn ON the ignition, with the engine OFF.
  4. Command the MIL ON and OFF using the scan tool. Repeat the commands as necessary.

Does the MIL turn ON and OFF when commanded?

--

Go to Step 3

Go to Step 4

3

  1. Observe the Freeze Frame/Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observe.

Does the DTC fail this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4

Inspect the fuse that supplies battery voltage to the MIL

Is the fuse open?

--

Go to Step 10

Go to Step 5

5

  1. Turn OFF the ignition.
  2. Disconnect the PCM. Refer to Powertrain Control Module Replacement .
  3. Turn ON the ignition.

Is the MIL OFF?

--

Go to Step 6

Go to Step 11

6

  1. Turn OFF the ignition.
  2. Remove the fuse that supplies voltage to the MIL.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a DMM from the MIL control circuit to a good ground.

Is the voltage at the specified value?

0 V

Go to Step 7

Go to Step 12

7

  1. Turn OFF the ignition.
  2. Reinstall the fuse that supplies voltage to the MIL.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the MIL control circuit in the PCM harness connector with a fused jumper wire connected to ground. Refer to Using Fused Jumper Wires in Wiring Systems.

Is the MIL ON?

--

Go to Step 15

Go to Step 8

8

  1. Turn OFF the ignition.
  2. Remove the IP. Refer to Instrument Cluster Replacement in Instrument Panel, Gauges, and Console.
  3. Probe the MIL battery positive voltage circuit at the IP harness connector with a test lamp connected to a good ground.

Is the test lamp illuminated?

--

Go to Step 9

Go to Step 13

9

Test the MIL control circuit for an open or high resistance and repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 18

Go to Step 14

10

Repair the short to ground in the battery positive voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 18

--

11

Repair the short to ground in the MIL control circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repairs?

--

Go to Step 18

--

12

Repair the short to voltage in the MIL control circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repairs?

--

Go to Step 18

--

13

Repair the open in the MIL battery positive voltage. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repairs?

--

Go to Step 18

--

14

Inspect for poor connections at the IP and repair as necessary. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 16

15

Inspect for poor connections at the PCM and repair as necessary. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 17

16

Replace the IP. Refer to Instrument Cluster Replacement in Instrument Panel, Gauges, and Console.

Did you complete the replacement?

--

Go to Step 18

--

17

Important: The replacement PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 18

--

18

  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 19

--

19

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK