Diagnostic Aids

Perform this test when instructed during QUICK TEST. Use this test only to diagnose:

• FPRC solenoid.
• Wiring harness circuits (FPRC and VPWR).
• Faulty Powertrain Control Module (PCM).

To prevent replacement of good components, be aware the following non-EEC areas may be cause of driveability concerns:

• Fuel pressure regulator.
• Engine not obtaining correct operating temperature.
• Vacuum hoses leaking or misrouted.
• Excessive internal engine wear or damage.
  Fig 1: Fuel Pressure Regulator Control (FPRC) Solenoid Circuit

  

1. Code 554: Enter Output State Diagnostic Test Mode (DTM)
   
   Code 554 indicates fault in FPRC circuit. Possible causes are:
   • Faulty FPRC solenoid.
   • Vacuum hoses leaking or misrouted.
   • Open or shorted circuit.
   • Faulty PCM.

   Enter Output State Diagnostic Test Mode (DTM). See OUTPUT STATE DIAGNOSTIC TEST MODE (DTM)  under ADDITIONAL SYSTEM FUNCTIONS. Once output state DTM has been entered, disconnect FPRC solenoid connector. Connect DVOM positive lead to VPWR circuit terminal at FPRC solenoid wiring harness connector. Connect DVOM negative lead to FPRC circuit terminal at FPRC wiring harness connector. Set DVOM to 20 volt scale. Observe DVOM and depress and release throttle several times to cycle solenoid output. If FPRC solenoid voltage increases to more than 1.0 volt, reconnect FPRC solenoid, remove jumper wire and go to next step. If FPRC solenoid does not increase to more than 1.0 volt, remove jumper wire and go to step 6).

2. Check Vacuum Hose
   
   Turn ignition off. Disconnect vacuum hose between manifold vacuum source and FPRC solenoid input port. Inspect vacuum hose for kinks, blockage and cracks. Replace hose as necessary. Repeat QUICK TEST  . If hose is okay, go to next step.
3. Check FPRC Vacuum Signal
   
   Turn ignition off. Using a vacuum tee, connect vacuum gauge between manifold vacuum source and FPRC solenoid input port. Start engine and observe vacuum gauge. If vacuum is present, remove vacuum gauge and go to next step. If vacuum is not present, check engine mechanical condition (valves, vacuum leaks, timing, EGR valve, etc.).
4. Check Vacuum Hose
   
   Turn ignition off. Disconnect vacuum hose between FPRC solenoid output port and fuel pressure regulator. Inspect vacuum hose for kinks, cracks and blockage. Replace hose as necessary. Repeat QUICK TEST  . If hose is okay, reconnect hose and go to next step.
5. Check FPRC Solenoid Operation
   
   Turn ignition off. Install vacuum gauge between FPRC solenoid output port and fuel pressure regulator. Perform road test as follows:
   • Warm engine to normal operating temperature.
   • Observe vacuum gauge and accelerate heavily to 40 MPH.
   • Observe vacuum gauge and decelerate to a steady cruise below 20 MPH.

   Vacuum gauge should indicate a low vacuum (FPRC solenoid closed) during heavy acceleration and a higher vacuum (FPRC solenoid open) during steady cruise if FPRC solenoid is functioning properly. Repeat test as necessary to confirm test results. If vacuum signal is as specified, remove vacuum gauge and check for fuel system malfunction. See FUEL SYSTEM in the SYSTEM/COMPONENT TESTS article. If vacuum signal is not as specified, replace FPRC solenoid. Repeat QUICK TEST  .

6. Check FPRC Solenoid VPWR
   
   Turn ignition off. Disconnect FPRC solenoid connector. Turn ignition on. Measure voltage between VPWR terminal at FPRC wiring harness connector and negative battery terminal. If voltage is 10.5 volts or less, repair open circuit and repeat QUICK TEST  . If voltage is more than 10.5 volts, go to next step.
7. Check FPRC Circuit Continuity
   
   Turn ignition off. Disconnect 60-pin PCM connector. Inspect connector for damaged pins, corrosion and loose wires. Repair as necessary. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Disconnect FPRC solenoid wiring harness connector. Measure resistance between test pin No. 32 and FPRC circuit terminal at FPRC solenoid wiring harness connector. If resistance is 5 ohms or more, repair open circuit. Repeat QUICK TEST  . If resistance is less than 5 ohms, go to next step.
8. Check FPRC Circuit For Short
   
   Leave ignition off and FPRC solenoid disconnected. Measure resistance between test pin No. 32 and test pins No. 37 and 57. Also, measure resistance between test pin No. 32 and test pins No. 40, 46 and 60. If any reading is 10,000 ohms or less, repair short circuit. Remove breakout box, reconnect all components, and repeat QUICK TEST  . If each reading is more than 10,000 ohms, replace PCM. Remove breakout box, reconnect all components, and repeat QUICK TEST  .