Fuel Pressure Regulator Control (FPRC) Solenoid

1994 PCED OBDI-A

SECTION 6A: EEC-IV Pinpoint Test
Procedures

KN: Fuel Pressure Regulator Control (FPRC) Solenoid

KN: Introduction

KN1 KOEO DIAGNOSTIC TROUBLE CODE (DTC) 554:
ENTER OUTPUT STATE DIAGNOSTIC TEST MODE (DTM)

For KOEO Diagnositc Trouble Code 554: Refer to Quick Test Appendix, Section 5A.

DTC 554 indicates a failure in the Fuel Pressure Regulator Control (FPRC) solenoid circuit.

Possible causes:

Damaged FPRC solenoid.
Damaged vacuum hose(s).
Open in harness.
Short (to power or ground) in harness.
Damaged Powertrain Control Module (PCM).

Note: Do not use STAR Tester for this step. Use a VOM/DVOM.

Key off.
Disconnect electrical connector on the speed control servo, if equipped.
DVOM on 20 volt scale.
Connect DVOM negative test lead to STO circuit at Data Link Connector (DLC) and positive test lead to battery positive.
Jumper STI circuit to SIG RTN at DLC.
Perform Key On Engine Off (KOEO) Self-Test until completion of Continuous Test Memory DTCs.
DVOM will indicate less than 1.0 volt when test is completed.
Depress and release throttle.

Does voltage increase?

Yes	No
REMAIN in Output State DTM. GO to KN2.	DEPRESS throttle to WOT and RELEASE. If STO voltage does not go high, leave equipment hooked up and GO to Pinpoint Test Step QC1.

KN2 CHECK FUEL PRESSURE REGULATOR CONTROL SOLENOID ELECTRICAL OPERATION

Key on, engine off.
Disconnect FPRC solenoid.
Connect DVOM positive test lead to VPWR pin and negative test lead to FPRC circuit at the FPRC solenoid vehicle harness connector.
DVOM on 20 volt scale.
While observing DVOM depress and release throttle several times to cycle solenoid output.

Does FPRC solenoid output voltage change greater than 1.0 volt?

Yes	No
RECONNECT FPRC solenoid. REMOVE jumper. GO to KN3.	REMOVE jumper. GO to KN7.

KN3 CHECK VACUUM HOSE BETWEEN THE MANIFOLD VACUUM SOURCE AND THE FPRC SOLENOID VACUUM INPUT PORT

Key off.
Disconnect and inspect vacuum hose between the manoifold vacuum source and the FPRC solenoid input vacuum port for blockage, kinks, cracks, etc.

Is vacuum hose in good condition?

Yes	No
RECONNECT vacuum hose. GO to KN4.	SERVICE OR REPLACE the vacuum hose as necessary. RERUN Quick Test.

KN4 CHECK VACUUM SIGNAL FROM MANIFOLD VACUUM SOURCE TO FPRC SOLENOID INPUT PORT

Key off.
Tee in a standard vacuum gauge at the hose between the manifold vacuum source and the FPRC solenoid input vacuum port.
Start and idle engine while observing the vacuum gauge needle.

Was a vacuum signal present?

Yes	No
REMOVE vacuum gauge. GO to KN5.	REFER to Probe service manual to address base engine vacuum source concern.

KN5 CHECK VACUUM HOSE BETWEEN THE FPRC SOLENOID OUTPUT PORT AND THE FUEL PRESSURE REGULATOR

Key off.
Disconnect and inspect the vacuum hose between the FPRC solenoid output port and the fuel pressure regulator for blockage, kinks, cracks, etc.

Is the vacuum hose in good condition?

Yes	No
RECONNECT the vacuum hose. GO to KN6.	SERVICE or REPLACE the vacuum hose as necessary. RERUN Quick Test.

KN6 EXERCISE THE FPRC SOLENOID VALVE

Key off.
Install vacuum gauge between the FPRC solenoid output port and the fuel pressure regulator.
Perform the road test as outlined below:

Warm engine to operating temperature.
Obey all local traffic laws.
Observe the vacuum gauge while

Accelerating heavily to 40 mph and
Decelerating to a steady cruise below 20 mph.

Note: Gauge should indicate a low vacuum (FPRC solenoid valve closed) during the heavy acceleration and a higher vacuum (FPRC solenoid valve open) during the steady cruise if the FPRC solenoid valve is functioning properly. Repeat the test as necessary to confirm status of the FPRC solenoid valve operation.

Did vacuum signal to fuel pressure regulator fall and rise as expected?

Yes	No
REMOVE the vacuum gauge. REFER to Section 9A for fuel pressure regulator diagnostics.	REMOVE the vacuum gauge. REPLACE the FPRC solenoid assembly. RERUN Quick Test.

KN7 CHECK FPRC SOLENOID VPWR

Key off.
FPRC solenoid disconnected.
Key on, engine off.
Measure voltage between VPWR at FPRC solenoid vehicle harness connector and battery ground.

Is voltage greater than 10.5 volts?

Yes	No
GO to KN8.	SERVICE open in VPWR harness circuit. RECONNECT FPRC solenoid. RERUN Quick Test and/or VERIFY elimination of drive symptom.

KN8 CHECK FPRC CIRCUIT CONTINUITY

Key off.
FPRC solenoid disconnected.
Disconnect Powertrain Control Module (PCM). Inspect for damaged or pushed out pins, corrosion, loose wires, etc. Service as necessary.
Install breakout box, leave PCM disconnected.
Measure resistance between Test Pin 13 (Test Pin 32 for CD4E and Calif. M/T) at the breakout box and FPRC circuit at solenoid vehicle harness connector.

Is resistance less and 5.0 ohms?

Yes	No
GO to KN9.	SERVICE open circuit. REMOVE breakout box. RECONNECT all components. RERUN Quick Test and/or VERIFY elimination of drive symptom.

KN9 CHECK FPRC CIRCUIT FOR SHORT TO POWER AND GROUND

Key off.
FPRC solenoid disconnected.
Breakout box installed, PCM disconnected.
Measure resistance between Test Pin 13 (Test Pin 32 for CD4E and Calif. M/T) and Test Pins 37 and 57 at the breakout box.
Measure resistance between Test Pin 13 (Test Pin 32 for CD4E and Calif. M/T) and Test Pins 40, 46 and 60 at the breakout box.

Is each resistance greater than 10,000 ohms?

Yes	No
REPLACE PCM. REMOVE breakout box. RECONNECT all components. RERUN Quick Test.	SERVICE short circuit. REMOVE breakout box. RECONNECT all components. RERUN Quick Test.

KN1 KOEO DIAGNOSTIC TROUBLE CODE (DTC) 554:ENTER OUTPUT STATE DIAGNOSTIC TEST MODE (DTM)