For 1990-2009 cars

### 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. The 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 component control circuit 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 ignition is ON.

### Conditions for Setting the DTC

• | An improper voltage level has been detected on the MIL control circuit.

• | The above condition is present for at least 30 seconds.

### Action Taken When the DTC Sets

The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

### Conditions for Clearing the MIL/DTC

• | A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

• | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• | Clear the MIL and the DTC with a scan tool.

### Diagnostic Aids

If the ignition feed circuit is suspected of being open, inspect the other bulbs which are powered by the same circuit.

If the condition is intermittent, refer to Intermittent Conditions .

### Test Description

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

1. Command both the ON and the OFF states. Repeat the commands as necessary.

2. If you do not find trouble in the control circuit or the connection at the PCM, the PCM may be faulty. However, this is an extremely unlikely failure.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 |

1. Turn ON the ignition, with the engine OFF.
2. Command the MIL ON and OFF using the scan tool.

Does the MIL turn ON and OFF with each command?

Go to Diagnostic Aids

Go to Step 3

3 |

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Turn ON the ignition.

Is the MIL OFF?

Go to Step 4

Go to Step 5

4 | Probe the MIL control circuit in the PCM harness connector with a fused jumper wire connected to ground. Is the MIL ON? | Go to Step 6 | Go to Step 7
5 | Repair the short to ground in the MIL control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 9 | --
6 | Test for poor connections at the PCM. Refer to Testing for Continuity and Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | Go to Step 9 | Go to Step 8
7 | Test for the following conditions:

• | Open ignition positive voltage to the MIL bulb

• | Control circuit open or shorted to battery positive voltage

Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 9

--

8 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | Go to Step 9 | --
9 |

1. Select the Diagnostic Trouble Code (DTC) option and the Clear DTC option using the scan tool.
2. Idle the engine at the normal operating temperature.
3. Select the Diagnostic Trouble Code (DTC) option and the Specific DTC option, then enter the DTC number using the scan tool.
4. Operate the vehicle within the Conditions for Setting this DTC as specified in the supporting text, if applicable.

Does the scan tool indicate that this test failed?

Go to Step 2

Go to Step 10

10 | 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