For 1990-2009 cars

Refer to

#### Power, Ground, MIL, and DLC

Engine Controls Components
Powertrain Control Module (PCM) General Description
Ignition Controls
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
for wiring view.

### Circuit Description

When the ignition is turned ON, the malfunction indicator lamp (MIL) will momentarily flash ON then OFF and remain ON until the engine is running, if no diagnostic trouble codes (DTCs) are stored. The powertrain control module (PCM) controls the MIL by providing a ground path through the MIL control circuit to turn ON the MIL.

### Diagnostic Aids

Any circuitry, that is suspected as causing an intermittent complaint, should be thoroughly checked for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminals to wiring connections or physical damage to wiring harness.

### Test Description

Number(s) below refer to step number(s) on the Diagnostic Table.

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool, if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is stored in the scan tool for later reference.

2. If the engine fails to start and the MIL is inoperational, then the fault can be isolated to either the PCM Ignition Positive Voltage #2, the Battery Positive Voltage B+, a poor PCM ground at the engine block, or the PCM.

3. A MIL that responds correctly to the scan tool commands indicates that the fault is not present at this time or conditions has been corrected.

4. Probing the MIL circuit with a test light to ground simulates the PCM's control of the MIL. If the MIL illuminates, then the fault can be isolated to the control of the MIL.

5. Locate and repair any shorts that may have caused the fuse to open before replacing the fuse.

6. If the Ignition Positive Voltage #3 is open, DTC's P0748 and P0753 may also be set (electronic automatic transmission only(.

7. Before replacing the PCM, check for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminals to wiring connections or physical damaged to the wiring harness. Replacement PCM's must be reprogrammed. Refer to the latest Techline information for programming procedures.

8. A shorted MIL circuit can be diagnosed with a scan tool. Refer to Powertrain Control Module Outputs Diagnosis .

9. An open MIL circuit can be diagnosed with a scan tool. Refer to Powertrain Control Module Outputs Diagnosis .

10. For MIL bulb replacement procedures, refer to Section 8C of the service manual.

11. For IPC replacement procedures, refer to Section 8C of the service manual.

12. PCM grounds will only cause a problem if all of the grounds are not making a good connection. If a PCM ground problem is suspected, the most probable place to check is where all the grounds meet, at the engine block.

#### No Malfunction Lamp (MIL) Check Engine

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Turn the ignition switch ON, with the engine OFF. Is the MIL ON? | -- | Go to Step 4 | Go to Step 3
3 | Attempt to start the engine. Does the engine start? | -- | Go to Step 5 | Go to Step 6
4 |

1. Install a scan tool.
2. Command the MIL ON and OFF.

Does the MIL turn ON and OFF when commanded?

--

Go to Step 22

Go to Step 5

5 |

1. Turn the ignition switch OFF.
2. Disconnect the PCM connectors from the PCM.
3. Turn the ignition switch ON.
4. Probe the MIL driver circuit with a test light connected to ground.

Is the MIL ON?

--

Go to Step 7

Go to Step 8

6 | Inspect the ignition and battery feed fuses. Are the fuses OK? | -- | Go to Step 9 | Go to Step 10
7 | With a test light connected to ground, probe the ignition positive voltage #3 circuit. Does the test light illuminate? | -- | Go to Step 11 | Go to Step 12
8 | Did the test light illuminate? | -- | Go to Step 13 | Go to Step 14
9 |

1. Turn the ignition switch OFF.
2. Disconnect the PCM connectors from the PCM.
3. Turn the ignition switch ON.
4. Probe the ignition positive voltage #2 circuit with a test light connected to ground.

Does the test light illuminate?

--

Go to Step 18

Go to Step 19

10 |

1. Check for a short to ground in the circuit of the fuse that was open and repair if necessary.
2. Replace the open fuse.

Is the action complete?

--

Go to Step 22

--

11 |

1. Check for faulty PCM connections.
2. If OK, replace the PCM.

Is the action complete?

--

Go to Step 22

--

12 | Repair the open in the ignition positive voltage #3. Is the action complete? | -- | Go to Step 22 | --
13 | Repair the short to voltage in the MIL control circuit. Is the action complete? | -- | Go to Step 22 | --
14 | Check for an open in the MIL control circuit and repair as necessary. Was a repair necessary? | -- | Go to Step 22 | Go to Step 15
15 | Check for an open in the ignition feed circuit or fuse to the MIL and repair as necessary. Was a repair necessary? | -- | Go to Step 22 | Go to Step 16
16 | Check for an open MIL bulb and replace if necessary. Was a bulb replacement necessary? | -- | Go to Step 22 | Go to Step 17
17 | Replace the IPC. Is the action complete? | -- | Go to Step 22 | --
18 | Probe the battery positive voltage B+ circuit with a test light connected to ground. Does the test light illuminate? | -- | Go to Step 20 | Go to Step 21
19 | Repair the open in the ignition positive voltage #2 circuit. Is the action complete? | -- | Go to Step 22 | --
20 | Check for a faulty PCM ground connection at the engine block and repair as necessary. Was a repair necessary? | -- | Go to Step 22 | Go to Step 11
21 | Repair the open in the battery positive voltage circuit. Is the action complete? | -- | Go to Step 22 | --
22 |

1. Allow engine to idle until normal operating temperature is reached.
2. Check if any DTC's are set.

Are any DTC's displayed that have not been diagnosed?

--

Go to the applicable DTC table

System OK