GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Express (CNG) 🢒 Engine 🢒 Engine Controls - 5.0L and 5.7L 🢒 Ignition Relay Diagnosis

Circuit Description

The ignition relay is the positive voltage supply source for the following components:

    • The fuel gage select switch
    • The lock-off relay
    • The idle control solenoid
    • The fuel control solenoid
    • The low pressure lock-off solenoid

The ignition relay coil is energized when the ignition switch is turned to the run or start positions. The ignition relay switch contact is supplied voltage at all times.

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. This step inspects the Alternative Fuels ECM fuses for opens and also tests the voltage supply to the fuses.

    3.

  3. This step inspects if the Alternative Fuels ECM is powered-up.

    4.

  4. This step tests the battery positive and switched ignition voltage circuits to the Alternative Fuels ECM.

    5.

  5. This step tests the Alternative Fuels ECM ground circuits.

    6.

  6. This step inspects for proper operation of the fuel gage select switch. If the switch operates then the ignition relay is ON.

    7.

  7. This step inspects the ignition relays ability to turn OFF.

    8.

  8. This step tests the ignition relay coils ground circuit. If the test lamp illuminates then the Ignition relay must be faulty.

    9.

  9. This step indicates the components or the circuits that may have caused a fuse to open. Some components may require they be turned ON in order to open the fuse. An example would be depressing the fuel gage select switch in order to test the select switch circuit for a short.

Step

Action

Yes

No

1

Did you perform the diagnostic system check?

Go to Step 2

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

2
  1. Turn the ignition ON, with the engine OFF.
  2. Inspect the CNG, ECM 1 and TRANS fuses.

Is any fuse open?

Go to Step 15

Go to Step 3

3

Probe both terminals of each fuse using the J 35616-200 Unpowered Test Lamp connected to a known good ground. Ensure that the ignition is ON and the engine is OFF.

With the fuses installed the probe test points for the fuses are visible at either side of the amperage rating.

Does the test lamp illuminate at all terminals?

Go to Step 5

Go to Step 4

4
  1. Inspect fuse terminal contact.
  2. Repair fuse terminal contact as necessary.
  3. Test the fuse supply source. Typically the source is a MAXI fuse, fusible link or a relay. Refer to Power Distribution Schematics in Wiring Systems in the G Van Service Manual.
  4. Repair the fuse supply source as necessary.

Are all repairs complete?

Go to Step 24

--

5

Using a scan tool, attempt to communicate and retrieve data from the Alternative Fuels ECM.

Does the scan tool display Alternative Fuels ECM data?

Go to Step 8

Go to Step 6

6

  1. Turn the ignition OFF.
  2. Disconnect the Alternative Fuels ECM connectors.
  3. Turn the ignition ON leaving the engine OFF.
  4. Probe the battery power and the ignition power circuit terminals at the Alternative Fuels ECM connectors with the J 35616-200 connected to a known good ground.

Does the test lamp illuminate at all terminals?

Go to Step 7

Go to Step 16

7

Probe all the Alternative fuels ECM Ground circuit terminals at the ECM connector with the J 35616-200 connected to BATTERY POSITIVE.

Does the test lamp illuminate at all terminals?

Go to Step 22

Go to Step 16

8

  1. Observe the fuel gage select switch data parameter on the scan tool.
  2. Depress and release the fuel gage select switch.

Did the fuel gage select switch data parameter indicate applied when the switch was depressed?

Go to Step 10

Go to Step 9

9

With the ignition ON, backprobe the ignition relay switch load terminal (87) with the J 35616-200 connected to a known good ground.

Is the test lamp illuminated?

Go to Fuel Gauge Relay Diagnosis - Alternative Fuels in the Instrument Panel, Gages, and Console section of the Alternative Fuels supplement

Go to Step 12

10
  1. Observe the alternative fuels engine speed data parameter on the scan tool.
  2. Observe the engine speed parameter as you crank and attempt to start the engine.

Is engine RPM displayed as you crank or start the engine?

Go to Step 11

Go to DTC P0336

11

  1. With the ignition ON, backprobe the ignition relay switch load terminal (87) with the J 35616-200 connected to a known good ground.
  2. Observe the test lamp as you turn the ignition OFF.

Is the test lamp illuminated with the ignition OFF?

Go to Step 17

System OK

12

With the ignition ON, backprobe the ignition relay switch supply terminal (30) with the J 35616-200 connected to a known good ground.

Is the test lamp illuminated?

Go to Step 13

Go to Step 18

13

With the ignition ON, backprobe the ignition relay coil supply terminal (85) with the J 35616-200 connected to a known good ground.

Is the test lamp illuminated?

Go to Step 14

Go to Step 19

14

  1. Disconnect the ignition relay connector.
  2. With the ignition ON, connect the J 35616-200 between the ignition relay coil supply terminal (85) and the ignition relay coil ground terminal (86).

Is the test lamp illuminated?

Go to Step 21

Go to Step 20

15

  1. Test for the short that caused the fuse to open.
  2. Possible shorts include the following:
    3. • CNG Fuse:
       - A shorted fuel gage select switch circuit
       - A shorted lock-off or fuel solenoid or circuit
       - A shorted Alternative Fuels ECM or Alternative Fuels ECM Battery Power circuit
    • ECM 1 Fuse:
       - A shorted Ignition Relay coil or circuit
       - A shorted base vehicle circuit. Refer to Power Distribution Schematics in Wiring Systems in the G Van Service Manual.
    • TRANS Fuse:
       - A shorted Alternative Fuels ECM or Alternative Fuels ECM Ignition Power circuit
       - A shorted base vehicle circuit. Refer to Power Distribution Schematics in Wiring Systems in the G Van Service Manual.
  3. Repair circuits or replace components as necessary.

Is the repair or replacement complete?

Go to Step 24

--

16

Repair the open in the Alternative Fuels ECM circuit that did not light the test lamp.

Is the repair complete?

Go to Step 24

--

17

Replace the stuck ignition relay or repair the Ignition Power circuit shorted to battery positive.

Is the repair or replacement complete?

Go to Step 24

--

18

Repair the open in the ignition relay switch supply circuit between the relay and the circuit splice.

Is the repair complete?

Go to Step 24

--

19

Repair the open in the ignition relay coil supply circuit between the relay and the circuit splice.

Is the repair complete?

Go to Step 24

--

20

Repair the open in the ignition relay coil ground circuit between the relay and ground.

Is the repair complete?

Go to Step 24

--

21

Replace the Ignition Relay.

Is the repair complete?

Go to Step 24

--

22
  1. Inspect for proper Alternative Fuels ECM terminal contact.
  2. Test for an open Class 2  serial data circuit between the splice and the Alternative Fuels ECM connector terminal.
  3. Repair terminal contact or wiring as necessary.

Was terminal contact or a wiring repair performed?

Go to Step 24

Go to Step 23

23
  1. Replace the Alternative Fuels ECM. Refer to Alternative Fuels Engine Control Module Replacement .
  2. Program the replacement control module with the correct vehicle software and calibration.

Is the replacement complete?

Go to Step 24

--

24
  1. Remove all test equipment except the scan tool.
  2. Connect any disconnected components, fuses, etc.
  3. Using a scan tool, clear DTC Information from the Alternative Fuels ECM 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)