GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2005 🢒 Isuzu MD F-Series 🢒 Engine 🢒 Engine Controls - 7.8L 🢒 Malfunction Indicator Lamp (MIL) Always On

Circuit Description

The battery positive voltage is supplied directly to the malfunction indicator lamp (MIL). The engine control module (ECM) turns the MIL ON by grounding the MIL control circuit.

MIL Operation

The MIL is located on the instrument panel (I/P).

MIL Function

    • The MIL informs the driver that a malfunction has occurred. The vehicle should be serviced as soon as possible.
    • The MIL illuminates during a bulb test, and during a system test.
    • A DTC will be stored if the diagnostic test requests a MIL.

MIL Illumination

    • The MIL will illuminate with ignition switch ON, and with the engine not running.
    • The MIL will turn OFF when the you start the engine.
    • The MIL will remain ON if the self-diagnostic system detects a malfunction.
    • The MIL may turn OFF if the malfunction is not present.
    • If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated if the ignition switch is ON.
    • If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, and cycled ON again.

Test Description

The number below refers to the step number on the diagnostic table.

  1. The step determines if the condition is with the MIL control circuit or the ECM.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Turn ON the ignition, with the engine OFF.

Does the malfunction indicator lamp (MIL) turn OFF when the ignition is turned ON?

Go to Step 5

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the engine control module (ECM). Refer to Engine Control Module Replacement/Restore Fuel Rate Data .
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the MIL.

Does the MIL illuminate?

Go to Step 4

Go to Step 7

4
  1. Remove the instrument panel cluster (IPC). Refer to Instrument Cluster Replacement .
  2. Test the MIL control circuit for a short to ground between the ECM and the IPC. Refer to Circuit Testing , and to Wiring Repairs .

Did you find and correct the condition?

Go to Step 8

Go to Step 6

5

Repair the MIL control circuit for a short to voltage. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 8

--

6

Replace the IPC. Refer to Instrument Cluster Replacement .

Did you complete the replacement?

Go to Step 8

--

7

Replace the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data .

Did you complete the replacement?

Go to Step 8

--

8

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2