Hummer H1 (2006+). Manual - part 55

OBD-64

On-Board Diagnostics

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DTC P0088 Rail Pressure too High (Figure OBD-20)

Figure OBD-20:   Fuel Pressure Regulator and Fuel Pressure Sensor Circuits

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.

Conditions for Setting the DT

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 informa-

tion in the Freeze Frame/Failure Records. 

• The control module will limit fuel injection and FRP. 

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 On-Board Diagnostics  OBD-65

5745804

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. 

Step

Action

Value(s)

Yes

No

    1

NOTE: Before clearing DTC(s) use the scan tool “Capture info” to
record Freeze Frame and Failure Records for reference, as data will be
lost when “Clear Info” function is used 

Was the “On-Board Diagnostic (OBD) System Check” performed?

Go to step 2.

Go to OBD 

System

Check.

    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 the 

Diagnostic

for 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. 
You may also operate the vehicle within the conditions that you 
observed from the Freeze Frame/Failure Records.

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:

• 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 pres-

sure 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 Diag-

nostic 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 509 (YL) for a short to ground. 

Did you find and correct the condition?

Go to Step 12

Go to Step 8

OBD-66

On-Board Diagnostics

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    8

Replace the faulty engine control module (ECM). 

Did you complete the replacement?

Go to Step 12 

    9

Test the FRP sensor signal circuit 509 (YL) for high resistance or an
open.

Did you find and correct the condition?

Go to Step 13 

Go to Step 10

   10

Replace the faulty FRP sensor.

Did you complete the replacement?

Go to Step 12

   11

Replace the FRP regulator. 

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. 
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 13

   13

1.

Using the Scan Tool select “Capture Info,” Review Info.” Are any 
DTC’s displayed that have not been diagnosed?

Go to the 

applicable

DTC table.

System OK.

Step

Action

Value(s)

Yes

No

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 On-Board Diagnostics  OBD-67

5745804

DTC P0089 Fuel Rail Pressure Regulator Performance (Figure OBD-21)

Figure OBD-21:   Fuel Pressure Regulator and Fuel Pressure Sensor Circuits

Circuit Description

The engine control module (ECM) uses commanded fuel pump flow to determine a desired fuel rail pressure (FRP). The actual fuel
pressure is monitored using the FRP sensor. If the FRP sensor indicates a pressure more than 20 MPa greater than desired, DTC
P0089 will set.

Conditions for Setting the DTC 

• The difference between the actual FRP and the desired FRP is more than 20 MPa. 

• The commanded fuel pump flow is 100 mm©¯/second or less. 

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 informa-

tion in the Freeze Frame/Failure Records. 

Conditions for Clearing the MIL/DTC  

• The control module turns OFF the 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.

• Use a scan tool in order to clear the MIL and the DTC.