GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Kodiak C-Series (Conventional) C6/C7/C8 🢒 Engine 🢒 Engine Controls - 7.8L 🢒 DTC P0091

Circuit Description

The suction control valve (SCV) is on the fuel supply pump and controls the suction fuel quantity to the fuel rail. The SCV is fully opened in normal state and increased drive current results in closing the orifice. The engine control module (ECM) calculates desired fuel rail pressure and fuel flow rate, and compares the desired fuel rail pressure to the actual rail pressure to determine the SCV position. When the actual fuel rail pressure is higher than the desired value, the SCV is closed to decrease the flow rate. If the ECM detects an excessively low SCV solenoid drive current, this DTC will set.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0091 Fuel Pressure Regulator Solenoid 1 Control Circuit Low Voltage

Conditions for Running the DTC
    • The ignition is ON.
    • The battery voltage is between 10-16 volts.
    • The fuel supply pump is normal.
    • The SCV operating duty is between 20-50 percent.
    • The deviation of the SCV cycle duty is less than 10 percent.

Conditions for Setting the DTC

The SCV solenoid operating current is less than 400 mA.

Action Taken When the DTC Sets
    • The ECM illuminates the malfunction indicator lamp (MIL) and reduced engine power indicator lamp, if equipped, when the diagnostic runs and fails.
    • The ECM records the operating conditions at the time the diagnostic fails. The ECM stores this information in the Failure Records.
    • The ECM limits accelerator operating range.
    • The ECM limits fuel injection quantity.
    • The ECM limits fuel rail pressure.
    • The ECM closes the exhaust gas recirculation (EGR) valve and holds to the closed position.
    • The ECM inhibits cruise control.
    • The ECM inhibits PTO control.

Conditions for Clearing the DTC
    • The MIL resets when the ignition is turned OFF.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • Clear the MIL and the DTC with a scan tool.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 1

Go to Diagnostic System Check - Vehicle

2
  1. Observe the 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.

Does the DTC fail this ignition?

--

Go to Step 3

Go to Intermittent Conditions

3
  1. Turn OFF the ignition.
  2. Disconnect the suction control valve (SCV) connector.
  3. Inspect for poor connections at the harness connector of the SCV.
  4. Repair the connections, as necessary.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Disconnect the SCV.
  3. Measure the resistance of the SCV solenoid coil.

Is the resistance within the specified range?

1.9-2.3 ohms at 20°C (68°F)

Go to Step 5

Go to Step 8

5
  1. Test the power supply circuits between the engine control module (ECM) and the SCV for the following conditions:
    2. • A short to ground
    • An open circuit
    • High resistance
  2. Repair the circuits, as necessary.

Did you find and correct the condition?

--

Go to Step 10

Go to Step 6

6
  1. Test the signal circuits between the ECM and the SCV for the following condition:
    2. • A short to ground
    • An open circuit
    • High resistance
  2. Repair the circuits, as necessary.

Did you find and correct the condition?

--

Go to Step 10

Go to Step 7

7
  1. Turn OFF the ignition.
  2. Disconnect the ECM.
  3. Inspect for poor connections at the harness connector of the ECM.
  4. Repair the connections, as necessary.

Did you find and correct the condition?

--

Go to Step 10

Go to Step 9

8

Important: The SCV is part of the fuel supply pump.

Replace the fuel supply pump. Refer to Fuel Injection Pump Replacement .

Did you complete the replacement?

--

Go to Step 10

--

9

Important: The new ECM must be programmed.

Replace the ECM. Refer to Engine Control Module Programming and Setup , Engine Control Module Replacement/Restore Fuel Rate Data , and Fuel Injector Flow Rate Programming .

Did you complete the replacement?

--

Go to Step 10

--

10
  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 11

11

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK