GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 Savana (CNG) 🢒 DTC 🢒 DTC P0336

Circuit Description

The gasoline control module (VCM/PCM or ECM) monitors the crankshaft position sensor (CKP) signal in order to determine engine speed. The gasoline control module signals engine speed to the Alternative Fuels ECM by pulse-width-modulating the engine speed signal circuit.

This DTC is used to indicate no engine speed signal is being monitored by the Alternative Fuels ECM while the MAF sensor signal indicates the crankshaft is rotating.

Conditions for Running the DTC
    • The engine is operating on alternative fuel for an initial failure. The Alternative Fuels ECM will run this DTC in gasoline mode after an initial alternative fuel mode failure.
    • No Alternative Fuels ECM MAF sensor DTCs are set this ignition cycle.
    • The MAP sensor signal indicates 105.23 kPa (31.07 in Hg) or less.
    • The mass air flow is more than 3 grams per second for 1 second continuously.

Conditions for Setting the DTC

The Alternative Fuels ECM does not monitor an engine speed signal during the 1 second that mass air flow is more than 3 grams per second.

Action Taken When the DTC Sets

The Alternative Fuels ECM will switch-over to gasoline fuel operation. Alternative fuel operation will not be attempted until the next ignition key cycle.

    • 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

Intermittent Condition

A fault not present indicates the condition that caused the DTC to set is intermittent and not currently present. Refer to the Intermittent Conditions diagnostic information located in Symptoms - Engine Controls. If any additional DTCs were stored proceed to the applicable DTC table in the order stated in Diagnostic System Check - Alternative Fuels (Engine Controls) .

Test Description

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

  1. This step determines if the condition affects the gasoline control module.

    2.

  2. This step determines if the fault is present.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

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

Go to Step 2

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

2

Using the scan tool, establish communication with the gasoline control module (VCM/PCM or ECM), and review DTC information.

Is this DTC also stored in the gasoline control module (VCM/PCM or ECM)?

Go to DTC P0336 in the Engine Controls section of G Van Service Manual

Go to Step 3

3

Crank and attempt to start the engine.

Does the engine start and run?

Go to Step  4

Go to Step 6

4
  1. Using the scan tool, establish communication with the Alternative Fuels ECM.
  2. Clear DTC information from the Alternative Fuels ECM.
  3. Turn OFF the ignition and wait 10 seconds.
  4. Start and idle the engine.

Does this DTC set?

Go to Step 6

Go to Step 5

5

The fault is not present. Refer to Diagnostic Aids.

Are any DTCs stored that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List

Go to Intermittent Conditions

6
  1. Turn the ignition OFF.
  2. Disconnect the PCM connector that contains the engine speed input signal circuit.
  3. Remove the engine speed input signal wire and terminal from the PCM connector.
  4. Reconnect the PCM connector leaving the signal wire and terminal removed from the connector.
  5. Turn the ignition ON while leaving the engine OFF.
  6. Observe the engine speed data parameter on the scan tool while communicating with the Alternative Fuel ECM.
  7. Using a fused jumper, momentarily ground the engine speed input signal wire and terminal while observing the engine speed data parameter.

Does the engine speed data parameter momentarily indicate engine speed when the signal wire is grounded?

Go to Step 10

Go to Step 7

7

Did the jumper fuse open?

Go to Step 8

Go to Step 9

8
  1. Test the engine speed signal circuit for a short to voltage condition.
  2. Repair wiring as necessary.

Was a wiring repair made?

Go to Step 13

Go to Step 11

9
  1. Test the engine speed signal circuit for an open or a short to ground condition.
  2. Inspect the Alternative Fuels ECM connector terminals for proper terminal contact.
  3. Repair terminal contact or wiring as necessary.

Was a terminal or wiring repair made?

Go to Step 13

Go to Step 11

10
  1. Inspect the gasoline control module (PCM) connector terminals for proper terminal contact.
  2. Repair the terminal contact as necessary.
  3. Inspect for a condition in which air flow more than 3 gm/s is indicated by the MAF sensor with the ignition ON, and the engine OFF.

Was a repair necessary?

Go to Step 13

Go to Step 12

11
  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 13

--

12

Important: The following control module replacement procedures must all be completed before attempting to operate the vehicle.

The following procedures are located in the G Van Service Manual.

  1. Replace the gasoline control module (VCM/PCM or ECM). Refer to Powertrain Control Module Replacement .
  2. Program the replacement control module with the correct vehicle software and calibration.

    3. Important: In order to perform the variation learn procedure, a switch-over to gasoline operation is necessary. Remove the CNG 20-amp fuse in order to perform the switch-over.

  3. Perform the Crankshaft Position System Variation Learn .

Is the replacement complete?

Go to Step 13

--

13
  1. Using a scan tool, clear the DTC information from both control modules.
  2. Operate the vehicle under the Conditions for Running the DTC.
  3. Using the scan tool parameter DTC STATUS, ensure that this DTC runs.

Did this DTC run and pass?

System OK

Go to Step 2