There are wiring diagrams in the builders manuals at:
https://www.gmupfitter.com/pdflists/view/6
DTC P0090
Fuel Pressure Regulator Control Circuit
Circuit/System Description
High pressure fuel is regulated by the fuel rail pressure (FRP) regulator mounted on the fuel injection pump. The FRP regulator is controlled by the engine control module (ECM). The FRP regulator has a solenoid supply voltage circuit and solenoid control circuit. The ECM monitors the current on the circuits to detect a failure.
Conditions for Running the DTC
The ignition is ON.
The commanded FRP regulator current is between 40-1,500 mA.
Conditions for Setting the DTC
The FRP regulator circuit current is not between 40-1,600 mA.
Action Taken When the DTC Sets
DTC P0090 is a Type A DTC.
The ECM commands the engine to operate in the Reduced Engine Power mode.
The message center displays Reduced Engine Power.
Conditions for Clearing the DTC
DTC P0090 is a Type A DTC.
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 condition will exist.
If the fuse that supplies voltage to terminal C1-76 of the ECM is open, this DTC will set.
Special Tools
CH-48027 Digital Pressure Gage
J 35616-200 Test Light Probe Kit
Circuit/System Verification
Turn ON the ignition and observe that the Desired FRP Regulator parameter and the FRP Regulator Command are at the same mA values. The FRP Regulator Command should be at 16 percent.
The fuel pressure difference between the Actual Fuel Rail Pressure and the Desired Fuel Rail Pressure should be less than 5 MPa.
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 data.
Circuit/System Testing
Important: Failure to allow the ECM communications to completely terminate with the scan tool may result in misdiagnosis.
If DTC U0105, is also set, refer to Diagnostic Trouble Code (DTC) List - Vehicle. See: Diagnostic Trouble Code Descriptions
Turn OFF the ignition until the ECM is powered down.
Disconnect the FRP regulator in-line connector.
Probe the solenoid control circuit terminal 2 with a test lamp connected to ground. The test lamp should not illuminate.
Important: A solenoid control circuit that is shorted to voltage will illuminate the test lamp on both the supply voltage circuit and the solenoid control circuit.
If the test lamp illuminates, test the solenoid control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
Turn ON the ignition.
Connect the test lamp between the solenoid supply voltage circuit, terminal 1 and a ground. The test lamp should illuminate.
If the test lamp did not illuminate, test the solenoid supply voltage circuit for an open or short to ground. If the circuit tests normal, replace the ECM.
Connect the test lamp between the solenoid supply voltage circuit, terminal 1 and the solenoid control circuit, terminal 2. The test lamp should illuminate.
If the test lamp did not illuminate, test the solenoid control circuit for an open. If the circuit tests normal, replace the ECM.
Test the harness between the inline connector and the FRP regulator for an open or short to voltage. If the circuits tests normal, replace the FRP regulator.
Repair Instructions
Important: During code clearing, the ECM must be powered down. Power down is achieved by turning off the ignition key and waiting for loss of communication, indicating power down. The time to power down may vary from vehicle to vehicle. After power down is achieved, turn the ignition key to the ON position and clear the trouble code using the scan tool clear code function and power down ECM. Repeat power down if the trouble code does not clear on first attempt.
