GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Cavalier (CNG) 🢒 DTC 🢒 DTC P1204

Circuit Description

The PCM controls fuel delivery and determines which fuel system the engine is operating on. The PCM controls the Low Pressure Lock-Off (LPL) solenoid, and the High Pressure Lock-Off (HPL) solenoid. The PCM commands the HPL solenoid open for 1 second at every ignition ON, in order to prime the CNG fuel system. The PCM commands the HPL, and the LPL open, when the engine is cranking or running on CNG. If the vehicle does not start and operate on CNG within 8 seconds, this DTC will set.

Conditions for Running the DTC
    • The engine is cranking.
    • CNG operation is not inhibited.

Conditions for Setting the DTC

The cranking time to start in CNG mode is more than 8 seconds.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
    • The control module switches over to gasoline fuel operation.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Test Description

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

  1. This step determines if a CNG specific DTC is causing the condition. If one of the listed DTCs is set, diagnose that DTC first.

    2.

  2. This step determines if the engine will start and idle.

    3.

  3. This step determines if the CNG fuel system is the cause of the concern.

    4.

  4. This step determines if the ignition system is the cause of the concern.

    5.

  5. This step tests the injector monitor circuit to the FICM. An open injector monitor circuit will set this DTC.

Step

Action

Value(s)

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Controls Connector End Views

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

Observe the DTC information with a scan tool.

Are there any DTCs set?

--

Go to Step 3

Go to Step 5

3

With a scan tool, select Captured Info in order to store the powertrain DTC information.

Did you complete the action?

--

Go to Step 4

--

4

  1. Turn ON the ignition, with the engine OFF.
  2. Observe the DTC information with a scan tool.

Does the scan tool display DTC P0005, P0191, P1209, P2146, or P2665?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 5

5

Attempt to start the engine.

Does the engine start and idle?

--

Go to Step 6

Go to Step 7

6
  1. Observe the Freeze Frame and/or the Failure records data for this DTC.
  2. Turn the ignition OFF for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame and/or the Failure records data.

Does the DTC fail this ignition cycle?

--

Go to Step 7

Go to Intermittent Conditions

7

  1. Turn ON the ignition, with the engine OFF.
  2. Observe the fuel rail pressure (FRP) sensor parameter with a scan tool.

Does the FRP display remain steady near the specified value?

310 kPa (45 psi)

Go to Step 8

Go to Fuel System Diagnosis

8

  1. Verify that there is good spark to the spark plugs. Refer to Electronic Ignition (EI) System Diagnosis in Engine Controls in the J Platform Service Manual.
  2. If an ignition condition is found, repair as necessary.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 9

9

  1. Turn OFF the ignition.
  2. Disconnect the FICM. Refer to Fuel Injector Control Module Replacement .
  3. Probe the injector monitor circuit with a test lamp connected to a good ground.
  4. Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

--

Go to Step 10

Go to Step 11

10

Test for an intermittent and for a poor connection at the FICM. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems in the J Platform Service Manual.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

11

Repair the open or short to ground on the injector monitor circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the J Platform Service Manual.

Did you complete the repair?

--

Go to Step 13

--

12

Replace the FICM. Refer to Fuel Injector Control Module Replacement .

Did you complete the replacement?

--

Go to Step 13

--

13
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 14

14

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK