GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Sierra - 2WD (LPG) 🢒 DTC 🢒 DTC P1215

Circuit Description

The Alternative Fuels ECM contains electronic devices called output driver modules. The output driver modules provide switchable outputs for operating solenoids, relays, telltales, and other devices. Each of the outputs has a status line that the Alternative Fuels ECM monitors.

In order for the status line to detect a failure, the state of the control circuit must be opposite of the commanded state. If the Alternative Fuels ECM is commanding an output ON, then 0 volts should be monitored by the status line. If the Alternative Fuels ECM is commanding an output OFF then the voltage supplied to the controlled device should be monitored by the status line.

This DTC sets when the Alternative Fuels ECM has detected a control circuit fault.

Monitored control circuits include the following components:

    • The Alternative Fuels Operation (AFO) Signal control circuit
    • The Low Pressure Lock-Off (LPL) solenoid control circuit
    • The High Pressure Lock-Off (HPL) solenoid control circuit

Conditions for Running the DTC

The engine is cranking or running.

Conditions for Setting the DTC

The Alternative Fuels ECM monitors a control circuit fault for at least 2 second continuously.

Action Taken When the DTC Sets
    • The Alternative Fuels ECM will switch over to gasoline operation on KL6 equipped vehicles.
    • The Alternative Fuels ECM will illuminate the MIL and store the DTC as History during 1 drive trip in which the diagnostic runs and fails.
    • The Alternative Fuels ECM will record operating conditions at the time the DTC sets. This information will be stored as Freeze Frame data.

Conditions for Clearing the MIL/DTC

    • The Last Test Failed status will clear when the DTC runs and passes.
    • The Alternative Fuels ECM will turn OFF the MIL after 3 consecutive drive trips that the DTC runs and passes.
    • The History status will clear after 40 consecutive WARM-UP cycles with NO failures of ANY DTC.
    • All DTC Information can be cleared with a scan tool.

Diagnostic Aids

This DTC may also set after service programming of the powertrain control module (PCM). Clear DTC Information after PCM programming is complete.

The scan tool Output Driver data displays are only functional when the vehicle is operating on CNG.

For an intermittent condition refer to Intermittent Conditions .

Test Description

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

  1. The AFO Signal data parameter is from the PCM and displays the observed state of the alternative fuels operation command circuit. The AFO Signal Command data parameter is from the alternative fuels ECM and displays the commanded state of the alternative fuels operation command circuit.

    2.

  2. The alternative fuels ECM should only command the HPL solenoid ON for about 2 seconds. If the test lamp is always OFF test for control circuit continuity. If the test lamp is always ON test for a control circuit shorted to ground.

Step

Action

Yes

No

1

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

Go to Step 2

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

2

  1. Turn ON the ignition, with the engine OFF.
  2. With the scan tool Alt. Fuel Engine Data selection, observe the AFO Signal and the AFO Signal Command displays.

Do both displays indicate the same information?

Go to Step 3

Go to Step 6

3
  1. Turn the ignition OFF for 30 seconds.
  2. Listen for audible operation of the fuel tank high pressure lock-off (HPL) solenoid as you rapidly turn the ignition back and forth between LOCK and RUN.

Does the HPL solenoid operate?

Go to Step 4

Go to Step 8

4

  1. With a scan tool clear the Alt. Fuels DTC Information.
  2. Feel or listen for audible operation of the underhood low pressure lock-off (LPL) by performing the following:
    3. • On KL6 models, start and idle the engine and with the scan tool Alt. Fuel Special Function selection command the LPL solenoid ON and OFF.
    • On KL8 models, feel or listen for audible operation of the underhood low pressure lock-off (LPL) as you crank the engine.
    • The engine may not start. Turn the ignition OFF for 30 seconds prior to every attempt to energize the LPL solenoid by cranking.

Does the LPL solenoid operate as the ignition is cranked or commanded?

Go to Step 5

Go to Step 12

5

  1. Start and idle the engine.
  2. With the scan tool Alt. Fuel Special Function selection, command the HPL Solenoid ON and OFF.
  3. Listen for audible operation of the fuel tank high pressure lock-off (HPL) solenoid as you command the HPL Solenoid ON and OFF.

Does the HPL operate as commanded?

Go to Diagnostic Aids

Go to Step 15

6

  1. Turn the ignition OFF.
  2. Disconnect the Alternative Fuels ECM connectors. Refer to Alternative Fuels Engine Control Module Replacement .
  3. Turn ON the ignition with the engine OFF.
  4. With the scan tool PCM Engine Data selection, observe the AFO Signal display.

Does the display indicate PCM?

Go to Step 7

Go to Step 16

7

  1. With a 3 amp fused jumper wire ground the AFO Signal circuit at the Alternative Fuels ECM connector terminal. If the jumper fuse opens repair the short to voltage on the AFO Signal circuit.
  2. With the scan tool PCM Engine Data selection, observe the AFO Signal display.

Does the display indicate AFECM?

Go to Step 23

Go to Step 17

8

With the J 35616-200 Unpowered Test Lamp test the Underhood Fuse Block AFS Maxifuse®.

Is the fuse OK?

Go to Step 9

Go to Fuel Lock-Off Relay Diagnosis

9

  1. With the scan tool PCM Special Function selection, command the Fuel Pump ON and OFF.
  2. Listen for audible operation of the Lock-off Solenoid Relay.

Does the relay operate ON and OFF as commanded?

Go to Step 10

Go to Fuel Lock-Off Relay Diagnosis

10

  1. Turn OFF the ignition.
  2. Remove the tank cover. Refer to Fuel Tank Cover Replacement .
  3. Disconnect the HPL solenoid connector.
  4. Probe the HPL power circuit terminal with the J 35616-200 Unpowered Test Lamp connected to a known good ground.
  5. Observe the test lamp as you turn ON the ignition with the engine OFF.

Did the test lamp illuminate for about 2 seconds and then turn OFF?

Go to Step 11

Go to Step 18

11

  1. Turn OFF the ignition.
  2. Probe the HPL power circuit terminal with the J 35616-200 Unpowered Test Lamp connected to the HPL Solenoid Control circuit.
  3. Observe the test lamp as you turn ON the ignition with the engine OFF.

Did the test lamp illuminate for about 2 seconds and then turn OFF?

Go to Step 25

Go to Step 19

12

  1. Turn OFF the ignition.
  2. Disconnect the LPL solenoid connector.
  3. Probe the LPL power circuit terminal with the J 35616-200 Unpowered Test Lamp connected to a known good ground.
  4. Observe the test lamp as you turn ON the ignition with the engine OFF.

Did the test lamp illuminate for about 2 seconds and then turn OFF?

Go to Step 13

Go to Step 20

13

  1. Turn OFF the ignition.
  2. Probe the LPL Solenoid Control circuit terminal with the J 35616-200 Unpowered Test Lamp connected to battery positive.
  3. Turn ON the ignition with the engine OFF.
  4. Observe the test lamp.

Is the test lamp illuminated?

Go to Step 21

Go to Step 14

14

Observe the test lamp as you crank the engine.

Does the test lamp illuminate while the engine is cranking?

Go to Step 26

Go to Step 22

15

Test the HPL Solenoid Control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

16

Test the AFO Signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

Go to Step 31

Go to Step 30

17
  1. Inspect the PCM for the correct Alternative Fuels software. Program the PCM if necessary.
  2. Test the AFO Signal circuit for continuity. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

Go to Step 31

Go to Step 24

18

Test the HPL solenoid power circuit for continuity between the solenoid and the fuel lock-off relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

Go to Step 31

Go to Fuel Lock-Off Relay Diagnosis

19

Test the HPL solenoid control circuit for continuity or a short to ground between the solenoid and the Alternative Fuels ECM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

Go to Step 31

Go to Step 23

20

Test the LPL solenoid power circuit for a continuity between the solenoid and the fuel lock-off relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

Go to Step 31

Go to Fuel Lock-Off Relay Diagnosis

21

Test the LPL solenoid control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

22

Test the LPL solenoid control circuit for continuity between the solenoid and the Alternative Fuels ECM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

Go to Step 31

Go to Step 23

23

Inspect for proper terminal contact at the alternative fuels ECM connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

Go to Step 31

Go to Step 29

24

Inspect for proper terminal contact at the PCM connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

Go to Step 31

Go to Step 30

25

Inspect for proper terminal contact at the HPL connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

Go to Step 31

Go to Step 27

26

Inspect for proper terminal contact at the LPL connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

Go to Step 31

Go to Step 28

27

Replace the HPL solenoid. Refer to High Pressure Lock-Off Solenoid Replacement .

Did you complete the replacement?

Go to Step 31

--

28

Replace the LPL solenoid. Refer to Low Pressure Lock-Off Solenoid Replacement .

Did you complete the replacement?

Go to Step 31

--

29

Replace the alternative fuels ECM. Refer to Alternative Fuels Engine Control Module Replacement .

Did you complete the replacement?

Go to Step 31

--

30

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 31

--

31
  1. Use the scan tool in order to clear the DTCs from the following control modules:
    2. • alternative fuels ECM
    • PCM
  2. Turn OFF the ignition for 30 seconds.
  3. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 32

Go to Step 2

32

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK