GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC K Sierra - 4WD (LPG) 🢒 Body and Accessories 🢒 Instrument Panel, Gages, and Console 🢒 Fuel Indicator Lamp Always On - Alternative Fuels

Circuit Description

The fuel indicator lamp (FIL) informs the driver what fuel the engine is operating on.

This vehicle utilizes a powertrain control module (PCM) and an alternative fuels engine control module (ECM) in order to control engine operation. The alternative fuels ECM controls CNG engine operation and the PCM controls gasoline engine operation. The alternative fuels ECM and the PCM are connected by the AFO Signal circuit. The alternative fuels ECM will command CNG engine operation by grounding the AFO Signal circuit. The PCM will turn OFF the FIL whenever the AFO Signal circuit is grounded.

The instrument panel gage fuse supplies the positive voltage source for the FIL. The PCM supplies 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.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check - Engine Controls (Alternative Fuels)?

Go to Step 2

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

2

Start and idle the engine.

Is the FIL illuminated?

Go to Step 3

Go to Intermittent Conditions in Engine Controls

3

Observe the operation of the other instrument panel (IP) gages and/or lamps.

Do all the IP indicators, except the FIL, operate correctly?

Go to Step 4

Go to Diagnostic System Check - Instrument Cluster in Instrument Panel, Gages and Console in the C/K Pickup Service Manual

4
  1. With the scan tool, communicate with the alternative fuels ECM and observe the AFO Signal and AFO Signal Command data parameters.
  2. Observe the data parameters as you crank and start the engine.

Do both data parameters indicate that the AF ECM is in control of engine fueling?

Go to Step 5

Go to Fuel System Unwanted Switch to Gasoline in Engine Controls

5
  1. Turn OFF the ignition.
  2. Disconnect the PCM connectors. Refer to Powertrain Control Module Replacement in Engine Controls in the C/K Pickup Service Manual.
  3. Turn ON the ignition, with the engine OFF.

Is the fuel indicator lamp illuminated?

Go to Step 6

Go to Step 7

6

Test the FIL Control circuit between the PCM connector terminal and the IP for a short to ground. Refer to Circuit Testing and Connector Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

Go to Step 8

Go to Diagnostic System Check - Instrument Cluster in Instrument Panel, Gages and Console in the C/K Pickup Service Manual

7

Important: KL6 models require a switchover to gasoline with a scan tool in order to perform the Crankshaft Position Variation Learn Procedure.

KL8 models do not require the Crankshaft Position Variation Learn Procedure.

Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls in the C/K Pickup Service Manual.

Did you complete the replacement?

Go to Step 8

--

8
  1. Remove all test equipment except the scan tool.
  2. Connect any disconnected components, fuses, etc.
  3. With a scan tool, clear DTC information from the alternative fuels ECM and the PCM.
  4. Turn the ignition OFF and wait 30 seconds.
  5. Observe the FIL.
  6. Start the engine and operate the vehicle.

Does the FIL operate for a 2 second bulb check and then turn OFF?

System OK

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