Malfunction Indicator Lamp (MIL) Always On. Geo Prizm 1996

For 1990-2009 cars

Schematic Reference: Refer to Engine Controls Schematics

### Circuit Description

There should be a steady MIL when the ignition is ON, prior to starting the engine. Battery ignition voltage is supplied to the MIL. The PCM will turn the MIL ON by grounding the control circuit at the PCM. A steady MIL with the engine running suggests a short to ground in the MIL control circuit, or a DTC is stored.

### Diagnostic Aids

An intermittent malfunction, may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections before component replacement.

• | Check for a shorted MIL control circuit between the PCM and the I/P Cluster Assembly.

• | A shorted I/P Cluster Assembly board may cause the MIL to stay on.

### Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

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

2. Disconnecting the PCM will determine whether the malfunction is caused by a short to ground in the MIL control circuit, or a faulty PCM.

Step | Action | Value | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check

2

1. Turn OFF the ignition.
2. Disconnect the PCM electrical connector C3 at the PCM.
3. Turn ON the ignition, leaving the engine OFF.

Is the MIL ON?

--

Go to Step 3

Go to Step 5

3

1. Inspect for a short to ground in the MIL control circuit between the PCM and the I/P Cluster Assembly.
2. Repair as necessary. Refer to Wiring Repairs in Wiring System.

Did you find and correct a condition?

--

Go to Step 6

Go to Step 4

4 | Repair or replace the I/P Cluster Assembly as necessary. Is the action complete? | -- | Go to Step 6 | --
5 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 6 | --
6 | Start the engine and observe the MIL. Does the MIL turn OFF in approximately 1 to 2 seconds after the engine is started? | -- | System OK | Go to the Applicable Diagnostic Table