GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The engine control module (ECM) monitors fuel rail pressure (FRP) using the FRP sensor. If the sensor indicates a pressure more than the commanded rail pressure plus a possible transitional overshoot, the ECM will set DTC P0088 for FRP too high.

DTC Descriptor

This diagnostic supports the following DTC:

DTC P0088 Fuel Rail Pressure (FRP) Too High

Conditions for Running the DTC

    • DTCs P0192, P0193, P0642 or P0643 are not set.
    • The ignition is ON.

Conditions for Setting the DTC

The actual fuel pressure is more than 167 MPa.

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.
    • The control module will limit fuel injection and FRP.

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 number below refers to the step number on the diagnostic table.

  1. DTC P0090 is a current flow problem in the FRP regulator circuit. This incorrect current draw could lead to incorrect fuel pressure. This hardware problem should be diagnosed before the performance DTC is checked.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check - Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Turn ON the ignition, with the engine OFF.
  2. Observe the Actual Fuel Rail Pressure parameter with a scan tool.

Is the Actual Fuel Rail Pressure parameter within the specified range?

1.1-1.4 MPa

Go to Step 3

Go to Step 6

3

Did DTC P0090 also set?

--

Go to DTC P0090

Go to Step 4

4

  1. Start the engine.
  2. Observe the Actual Fuel Rail Pressure on the scan tool.
  3. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.

Is the Actual Fuel Rail Pressure more than the specified value?

167 MPa

Go to Step 11

Go to Step 5

5

  1. Start and idle the engine.
  2. Perform the following test at idle and at 2,000 RPM:
  3. • Change the fuel pressure with a scan tool, incrementing through the entire fuel pressure range.
    • Observe the actual vs desired fuel pressures at each fuel pressure level.

Does the fuel pressure increment and stabilize through the entire fuel pressure range, with actual and desired fuel pressure within 2 MPa of each other at every fuel pressure?

--

Go to Diagnostic Aids

Go to Step 11

6

  1. Disconnect the fuel rail pressure (FRP) sensor.
  2. Observe the Actual Fuel Rail Pressure parameter with a scan tool.

Does the Actual Fuel Rail Pressure measure more than the specified value?

175 MPa

Go to Step 9

Go to Step 7

7

Test the FRP sensor signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 8

8

Replace the engine control module (ECM). Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 12

--

9

Test the signal circuit of the FRP sensor for a high resistance or an open. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

10

Replace the FRP sensor. Refer to Fuel Injection Fuel Rail Fuel Pressure Sensor Replacement .

Did you complete the replacement?

--

Go to Step 12

--

11

Replace the FRP regulator. Refer to Fuel Pressure Regulator Replacement .

Did you complete the replacement?

--

Go to Step 12

--

12

  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 .

Does the DTC fail this ignition?

--

Go to Step 2

Go to Step 13

13

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK