GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Cavalier (CNG) 🢒 Engine 🢒 Engine Controls - 2.2L (LN2) 🢒 Malfunction Indicator Lamp (MIL) Always On

Object Number: 621490 Size: SF
Engine Controls Components
Engine Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The malfunction indicator lamp (MIL) is used to indicate to the driver of the vehicle that an engine control system condition has occurred that may cause an increase in emissions and/or cause a driveability concern.

When the ignition is first turned ON the gasoline control module (VCM/PCM or ECM) will illuminate the MIL for a bulb and system check. When the engine is started and operating the gasoline control module will turn the MIL OFF if no DTCs are set.

The AF ECU connects into the normal MIL Control circuit path and does not affect the gasoline control module operation of the MIL. The AF ECU is connected into the MIL Control circuit path in order to command the MIL ON when a CNG DTC sets. Both the AF ECU and the gasoline control module simultaneously test certain DTCs regardless of the fuel system that is in operation and may illuminate the MIL.

The instrument panel gauge fuse supplies the positive voltage source for the MIL. The gasoline control module and/or the AF ECU can supply the ground path.

Test Description

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

  1. The System Check MUST be performed before proceeding with this diagnostic table. Failure to perform the System Check will result in mis-diagnosis.

    2.

  2. With the ignition ON and the engine OFF the gasoline control module (VCM/PCM or ECM) should continuously illuminate the MIL.

    3.

  3. The scan tool will command BOTH the gasoline control module and the AF ECU to turn the MIL OFF.

    4.

  4. This step tests if the MIL Input circuit is requesting MIL illumination. There should not be a MIL Input while the MIL is commanded OFF.

Step

Action

Yes

No

1

Were you sent here from other diagnostic service information?

Go to Step 2

Go to Diagnostic System Check - Alternative Fuels (Engine Controls)

2

Turn the ignition ON with the engine OFF.

Is the MIL continuously illuminated?

Go to Step 3

Go to Malfunction Indicator Lamp (MIL) Inoperative

3

While communicating with the AF ECU, command the MIL OFF.

Is the MIL illuminated?

Go to Step 5

Go to Step 4

4

The fault is not present. Refer to Diagnostic Aids.

Is an operational concern still present?

Go to Diagnostic System Check - Alternative Fuels (Engine Controls)

Go to Intermittent Conditions

5

Observe the Gasoline MIL Command data parameter in the Alt. Fuels Data List while the MIL is commanded OFF.

Is a gasoline MIL Command request present?

Go to Step 7

Go to Step 6

6
  1. Test the MIL Control circuit between the AF ECU connector terminal and the IP for a short to ground.
  2. Test the IP for an internally shorted condition.
  3. Repair the circuit or IP as necessary.

Was a repair necessary?

Go to Step 9

Go to Step 8

7
  1. Test the MIL INPUT circuit between the AF ECU connector terminal and the gasoline control module connector terminal for a short to ground.
  2. Repair the circuit as necessary.

Was a circuit repair necessary?

Go to Step 9

Go to Step 8

8
  1. Replace the AF ECU. Refer to Engine Control Unit Replacement .
  2. Program (flash) the replacement control module with the correct vehicle software and calibration.

Is the replacement complete?

Go to Step 9

--

9
  1. Remove all test equipment except the scan tool.
  2. Connect any dis-connected components, fuses, etc.
  3. Using a scan tool, clear DTC information from the AF ECU and the gasoline control module (VCM/PCM or ECM).
  4. Turn the ignition OFF and wait 30 seconds.
  5. Start the engine and operate the vehicle.
  6. Observe the fuel indicator lamp and the MIL.
  7. Observe vehicle performance and driveability.
  8. After operating the vehicle inspect BOTH control modules for stored DTCs.

Does the vehicle operate on CNG with normal driveability, no FIL/MIL illumination and no stored DTCs?

System OK

Go to Diagnostic System Check - Alternative Fuels (Engine Controls)