GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Generic 🢒 2004 🢒 Unit Repair 🢒 DTC 🢒 DTC P1020

Circuit Description

The PCM controls fuel delivery and determines fuel system operation on Bi-fuel (KL6) vehicles. The PCM is not capable of operating the high current CNG fuel injectors. When CNG operation is commanded, the PCM grounds the AF enable circuit, which energizes the AF relay. The AF relay energizes all of the AF injector relays. The PCM injector control signals are routed through the AF injector relays to the fuel injector control module (FICM). The FICM generates duplicate control signals in order to operate the CNG injectors. When gasoline operation is commanded, the PCM opens the AF enable circuit, which de-energizes the AF relay, and all of the AF injector relays. The fuel injector control circuits are routed through the AF injector relays to the gasoline fuel injectors. A fused ignition voltage is supplied to all of the fuel injectors. The PCM monitors the status of each injector signal circuit. DTC P1020 will set if there is condition on any one of the fuel injector signal circuits, or AF injector relays.

Conditions for Running the DTC
    • DTC P0336 is not set.
    • The ignition voltage is between 6 and 18 volts.
    • The engine speed is more than 50 RPM.
    • The PCM is not in fuel shut-off, or decel fuel cut-off mode.

Conditions for Setting the DTC
    • The PCM detects a condition on a fuel injector control signal.
    • The condition exists for 5 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.

Diagnostic Aids
    • A stuck AF injector relay may cause this DTC to set.
    • For an intermittent condition, refer to Intermittent Conditions .

Test Description

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

  1. The step determines if the condition exists. When DTC P1020 sets, the vehicle will switch over to gasoline operation.

    2.

  2. The step determines if the condition affects CNG and gasoline operation.

    3.

  3. This step tests the fuel injector control circuit from the PCM to the AF injector relay. If the test lamp blinks, the PCM and wiring are OK.

    4.

  4. This step determines if a ground is constantly applied to the fuel injector control circuit.

    5.

  5. This step tests the fuel injector signal circuit from the FICM. If the test lamp illuminates, the FICM and wiring are OK.

    6.

  6. This step isolates the inoperative AF injector relay. Remove the AF injectors from the mounting bracket in order to prevent misdiagnosis.

    7.

  7. This step tests the ignition voltage circuits to each AF injector relay coil.

    8.

  8. This step tests the ground circuits to each AF injector relay coil.

Step

Action

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
  1. Turn OFF the ignition for 30 seconds.
  2. Start and idle the engine.
  3. Observe the DTC information with a scan tool.

Did DTC P1020 fail this ignition cycle?

Go to Step 4

Go to Step 3

3
  1. Observe the Freeze Frame/Failure Records for this DTC.
  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 4

Go to Diagnostic Aids

4
  1. Idle the engine at the normal operating temperature.
  2. Monitor the misfire current counters with a scan tool.

Are any of the misfire current counters incrementing?

Go to Step 5

Go to Step 7

5
  1. Turn OFF the ignition.
  2. Disconnect the harness connector of the AF fuel injector relay which displays the highest level of misfire.
  3. Probe the fuel injector control circuit from the PCM with a test lamp connected to B+.
  4. Idle the engine, while observing the test lamp.

Does the test lamp blink?

Go to Step 15

Go to Step 6

6

Does the test lamp remain illuminated?

Go to Step 14

Go to Step 13

7

Observe the DTC information with a scan tool.

Are any of the DTCs P0201-P0204 also set?

Go to Step 8

Go to Step 9

8
  1. Turn OFF the ignition.
  2. Disconnect the harness connector of the appropriate AF fuel injector relay.
  3. Probe the injector signal circuit, from the FICM, 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 15

Go to Step 12

9
  1. Turn OFF the ignition.
  2. Remove all of the AF injector relays from the mounting bracket.
  3. Command the AF enable relay ON and OFF with a scan tool.
  4. Feel for operation of each AF injector relay while commanding the AF enable relay ON and OFF.
  5. Isolate the inoperative relay.

Did you complete the action?

Go to Step 10

--

10
  1. Turn OFF the ignition.
  2. Disconnect the harness connector of the isolated AF fuel injector relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ignition voltage circuit of the AF injector relay with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 11

Go to Step 18

11

Probe the ground circuit of the AF injector relay with a test lamp connected to B+.

Does the test lamp illuminate?

Go to Step 15

Go to Step 19

12

Test the signal circuit of the fuel injector for an open, or a short to ground between the FICM and the relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the J Platform Service Manual.

Did you find and correct the condition?

Go to Step 23

Go to Step 16

13

Test the control circuit of the fuel injector for an open, or a short to voltage between the PCM and the relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the J Platform Service Manual.

Did you find and correct the condition?

Go to Step 23

Go to Step 17

14

Test the control circuit of the fuel injector for a short to ground between the PCM and the relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the J Platform Service Manual.

Did you find and correct the condition?

Go to Step 23

Go to Step 22

15

Test for an intermittent and for a poor connection at the AF injector relay. 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 23

Go to Step 20

16

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 23

Go to Step 21

17

Test for an intermittent and for a poor connection at the PCM. 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 23

Go to Step 22

18

Repair the open or short to ground on the appropriate ignition voltage circuit of the AF injector relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the J Platform Service Manual.

Did you complete the repair?

Go to Step 23

--

19

Repair the open on the appropriate ground circuit of the AF injector relay. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the J Platform Service Manual.

Did you complete the repair?

Go to Step 23

--

20

Replace the AF injector relay.

Did you complete the replacement?

Go to Step 23

--

21

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

Did you complete the replacement?

Go to Step 23

--

22

Replace the PCM. Refer to Powertrain Control Module Replacement in the J Platform Service Manual.

Did you complete the replacement?

Go to Step 23

--

23
  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 24

24

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