Ignition voltage is supplied directly to the malfunction indicator lamp (MIL). The engine control module (ECM) controls the lamp by grounding the control circuit through 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 ECM. When the ECM is commanding a component ON, the voltage of the control circuit should be low, near 0 volts. When the ECM 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 DTC to set.
• | The engine speed is more than 400 RPM. |
• | The ignition voltage is between 6-18 volts. |
• | The ECM 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. |
• | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
• | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records. |
• | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
• | 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. |
The numbers below refer to the step numbers on the diagnostic table.
This step tests for a short to ground in the MIL control circuit. With the ECM disconnected and the ignition ON the MIL should be OFF.
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.
This vehicle is equipped with a ECM that utilizes an electrically erasable programmable read only memory (EEPROM). When the ECM is being replaced, the new ECM must be programed.
Step | Action | Values | Yes | No |
---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
2 |
Does the MIL turn ON and OFF when commanded? | -- | Go to Step 3 | Go to Step 4 |
3 |
Does the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids |
4 | Inspect the fuse that supplies battery positive voltage to the MIL. Is the fuse open? | -- | Go to Step 10 | Go to Step 5 |
Is the MIL OFF? | -- | Go to Step 6 | Go to Step 11 | |
Does the voltage measure the specified value? | 0 V | Go to Step 7 | Go to Step 12 | |
7 |
Does the MIL illuminate? | -- | Go to Step 15 | Go to Step 8 |
8 |
Does the test lamp illuminate? | -- | 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 repair? | -- | Go to Step 18 | -- |
12 | Repair the short to voltage on the MIL control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 18 | -- |
13 | Repair the open in the MIL battery positive voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | 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 ECM 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 repair? | -- | Go to Step 18 | -- |
Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the repair? | -- | Go to Step 18 | -- | |
18 |
Does the DTC run and pass? | -- | Go to Step 19 | Go to Step 2 |
19 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK |