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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Engine 🢒 Engine Controls - 6.6L (LLY) 🢒 DTC P0090

Circuit Description

The engine control module (ECM) supplies power and ground to the fuel rail pressure (FRP) regulator. The ECM monitors current on the circuits to detect a failure. If the current is outside of the expected range, DTC P0090 will set.

DTC Descriptor

This diagnostic supports the following DTC:

DTC P0090 Fuel Pressure Regulator Control Circuit

Conditions for Running the DTC
    • The ignition is ON.
    • The commanded FRP regulator current is between 400-1,500 mA.

Conditions for Setting the DTC

The FRP regulator circuit current is not between 50-1,600 mA.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
    • 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

There are no driveability concerns associated with the FRP regulator unless a DTC is present. The most likely cause of this DTC is a sticking FRP regulator.

If the fuel system pressure is actually too high, a fuel knock and smoke condition will exist.

Test Description

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

  1. This step tests for battery voltage through the ECM to the FRP regulator.

    2.

  2. This step tests for an open control circuit between the ECM and the FRP regulator.

    3.

  3. This excessive current code can be set by voltage being applied between the ECM and the FRP regulator on the FRP control circuit.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Is DTC U0105 present also?

--

Go to DTC U0100-U0299 in Data Link Communications

Go to Step 3

3

    Important: Failure to wait until there is no engine control module (ECM) communications with the scan tool will result in misdiagnosis.

  1. Turn OFF the ignition for 30 seconds.
  2. Turn ON the ignition, with the engine OFF.
  3. Observe the FRP Regulator Command parameter with a scan tool.

Is the FRP Regulator Command more than the specified value?

20%

Go to Step 4

Go to Step 18

4

Attempt to start the engine.

Does the engine start?

--

Go to Step 5

Go to Step 6

5
  1. Start the engine.
  2. Observe the Actual Fuel Rail Pressure and the Desired Fuel Rail Pressure with a scan tool.

Does the scan tool display a pressure difference more than the specified value?

5 MPa

Go to Step 7

Go to Diagnostic Aids

6

  1. Turn OFF the ignition.
  2. Disconnect the engine control module (ECM) connectors.
  3. Disconnect the fuel rail pressure (FRP) regulator connector.
  4. Measure the resistance from the control circuit of the FRP regulator to ground with a DMM.

Does the resistance measure at the specified value?

∞

Go to Step 15

Go to Step 12

7

  1. Turn OFF the ignition.
  2. Disconnect the FRP regulator harness connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the supply circuit of the fuel rail pressure regulator with a J 35616-200 Unpowered Test Lamp connected to a good ground. Refer to Troubleshooting with a Test Lamp in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step 8

Go to Step 11

8

  1. Turn OFF the ignition.
  2. Verify the FRP regulator harness connector is disconnected.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the control circuit of the FRP regulator with a J 35616-200 connected to battery voltage. Refer to Troubleshooting with a Test Lamp in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step 13

Go to Step 9

9

  1. Disconnect the ECM connector containing the FRP regulator control circuit.
  2. Turn ON the ignition, with the engine OFF.
  3. Measure the voltage from the FRP regulator control circuit to a good ground with a DMM.

Does the voltage measure the specified value?

0 V

Go to Step 16

Go to Step 11

10

Test for an open in the FRP supply circuit between the ECM and the FRP regulator.

If a condition is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 17

11

Repair the short to voltage in the control circuit between the ECM and the FRP regulator. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 19

--

12

Test for a short to ground in the control circuit between the ECM and the FRP regulator. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 18

13

Test the ignition voltage, fuel pressure regulator solenoid command, and fuel pressure regulator solenoid supply voltage circuits for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 14

14
  1. Test for an intermittent and for a poor connection at the FRP regulator. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
  2. Repair the wiring as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 15

15

Replace the FRP regulator. Refer to Fuel Injection Pump Replacement .

Did you complete the replacement?

--

Go to Step 19

--

16

Test for an open in the control circuit between the ECM and the FRP regulator. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 17

17
  1. Inspect for poor connections at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. Repair the wiring as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 19

Go to Step 18

18

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 19

--

19
  1. Clear the DTCs with the 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 20

20

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