Diagnostic Aids

WARNING: This page is about a different car, the 1995 Mazda MX-6 and 1995 Mazda 626. However, it is still accessible from the selected car via links, so may be relevant.

Perform this test when instructed during QUICK TEST. This test is intended to diagnose:

PRC solenoid valve.
Wiring harness circuits (PRC 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.

1) KOEO Code 554: Enter OUTPUT STATE CHECK Code 554 indicates fault in PRC solenoid vale circuit. Possible causes are:

Faulty RPC solenoid valve.
Vacuum hoses leaking or misrouted.
Open or shorted circuit.
Faulty PCM.

Use only VOM or DVOM for this step. DO NOT use scan tester. Turn ignition off. Disconnect cruise control servo. Connect DVOM negative lead to STO terminal at Data Link Connector (DLC). Connect positive lead to positive battery terminal. Install a jumper wire between STI terminal and SIG RTN terminal at DLC. Perform KOEO SELF-TEST until continuous memory test is complete. DVOM will read less than one volt when test is complete to indicate PCM has entered OUTPUT STATE CHECK. Depress and release throttle. If voltage increases, remain in OUTPUT STATE CHECK and go to next step. If voltage does not increase, depress throttle to WOT and release. If voltage increases, remain in OUTPUT STATE CHECK and go to next step. If voltage does not increase, leave test equipment connected and go to TEST QC.

2) Check PRC Solenoid Valve Operation Disconnect PRC solenoid valve. Turn ignition on. Connect DVOM positive lead to VPWR terminal and negative lead to PRC terminal at PRC solenoid valve wiring harness connector. Observe DVOM while depressing and releasing throttle several times to cycle solenoid valve output. If PRC solenoid valve output voltage varies one volt or less, remove jumper wire and go to step 7). If PRC solenoid valve output voltage varies more than one volt, reconnect PRC solenoid valve, remove jumper wire and go to next step.

3) Check Vacuum Hose Turn ignition off. Disconnect vacuum hose between manifold vacuum source and PRC solenoid valve 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.

4) Check PRC Vacuum Signal Warm engine to normal operating temperature. Turn ignition off. Using a vacuum tee, connect vacuum gauge between manifold vacuum source and PRC solenoid valve input port. Start engine and observe vacuum gauge for 5 minutes. 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.).

5) Check Vacuum Hose Turn ignition off. Disconnect vacuum hose between PRC solenoid valve 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.

6) Check PRC Solenoid Valve Operation Turn ignition off. Install vacuum gauge between PRC solenoid valve 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 (PRC solenoid valve closed) during heavy acceleration and a higher vacuum (PRC solenoid valve open) during steady cruise if PRC solenoid valve is functioning properly. Repeat test as necessary to confirm test results. If vacuum signal is as specified, remove vacuum gauge and go to next step. If vacuum signal is not as specified, replace PRC solenoid valve. Repeat QUICK TEST.

7) Check PRC Solenoid Valve VPWR Turn ignition off. Disconnect PRC solenoid valve. Turn ignition on. Measure voltage between VPWR terminal at PRC 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.

8) Check PRC Circuit Continuity Turn ignition off. Disconnect PRC solenoid valve. Disconnect PCM 60-pin connector and inspect for damaged pins, corrosion and loose wires. Repair as necessary. Install Breakout Box (49-UN01-058), leaving PCM disconnected. Measure resistance between test pin No. 32 at breakout box and PRC terminal at PRC solenoid valve 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.

9) Check PRC Circuit For Short Turn ignition off. Disconnect PRC solenoid valve. With breakout box installed and PCM disconnected, measure resistance between test pin No. 32 and test pins No. 37 and 57 at breakout box. Also, measure resistance between test pin No. 32 and test No. 40, 46 and 60 at breakout box. If any resistance is 10,000 ohms or less, repair short circuit. Remove breakout box, reconnect all components and repeat QUICK TEST. If each resistance is more than 10,000 ohms, replace PCM. Remove breakout box, reconnect all components and repeat QUICK TEST.