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.

PCM controls cooling fan operation through High Fan Control (HFC) and Low Fan Control (LFC) outputs. LFC and HFC relays are normally open. Perform this test only when directed here by QUICK TEST or a driveability symptom. This test is intended to diagnose:

Wiring harness circuits (LFC, HFC and IGN/RUN).
LFC and HFC relays.
Powertrain Control Module (PCM).

1) KOEO Codes 563 Or 564: Check For Voltage At LFC/HFC Relays Code 563 indicates faulty HFC circuit. Code 564 indicates faulty LFC circuit. Possible causes for these faults are:

Open or shorted circuit.
Faulty fan relay(s).
Faulty PCM.

Turn ignition off. Disconnect LFC and HFC relays. Turn ignition on. Measure voltage between IGN/RUN circuit at LFC/HFC relay wiring harness connector and chassis ground. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, check fuse/fuse link. Repair as necessary. If fuse/fuse link is okay, repair open circuit and repeat QUICK TEST.

2) Enter OUTPUT STATE CHECK Use only VOM or DVOM for this step. 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 to more than 10.5 volts, stay in OUTPUT STATE CHECK and go to next step. If voltage does not increase to at least 10.5 volts, depress throttle to wide open throttle and release. If STO voltage does not increase to at least 10.5 volts, leave equipment connected and go to TEST QC, step 2).

3) Check For LFC/HFC Circuit Cycling With vehicle still in OUTPUT STATE CHECK, disconnect LFC or HFC relay(s). Connect positive lead of DVOM to IGN/RUN terminal at LFC/HFC relay wiring harness connector and negative test lead to LFC or HFC coil terminal at LFC/HFC relay wiring harness connector. Depress throttle to cycle outputs off. Observe DVOM and depress throttle again. For LFC, wait until Malfunction Indicator Light (MIL) flashes once (about 10 seconds). For HFC, wait until MIL flashes twice (about 15 seconds). Release throttle. LFC/HFC output is now on. To cycle off output, depress and release throttle. If voltage cycles (about a 1-volt change), replace LFC or HFC relay(s). Remove jumper wire and repeat QUICK TEST. If voltage does not cycle, remove jumper wire and go to next step.

4) Check LFC/HFC Circuit Continuity Turn ignition off. Disconnect LFC or HFC relay(s). Disconnect 60-pin PCM connector and inspect for damaged pins, corrosion and loose wires. Repair as necessary. Install Breakout Box (49-UN01-058), leaving PCM disconnected. Set DVOM on 200-ohm scale. Perform appropriate following check:

Code 563

Measure resistance between HFC test pin No. 31 at breakout box and HFC terminal at each HFC relay wiring harness connector.

Code 564

Measure resistance between LFC test pin No. 13 at breakout box and LFC terminal at LFC relay wiring harness connector.

For either code, if resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit. Remove breakout box, reconnect all components and repeat QUICK TEST.

5) Check LFC/HFC Circuit For Short To Power Disconnect LFC or HFC relay(s). Turn ignition on. Measure voltage between LFC or HFC test pin at breakout box and negative battery terminal. If voltage is less than one volt, go to next step. If voltage is one volt or more, repair short circuit. Remove breakout box, reconnect all components and repeat QUICK TEST. If code is still present, replace PCM.

6) Check LFC/HFC Circuit For Short To Ground Turn ignition off. Disconnect PCM. Disconnect LFC or HFC relay(s). Measure resistance between LFC or HFC test pin and test pins No. 40 and 60 at breakout box. If resistance is more than 10,000 ohms, replace PCM. Remove breakout box, reconnect all components and repeat QUICK TEST. If resistance is 10,000 ohms or less, repair short circuit. Remove breakout box, reconnect all components and repeat QUICK TEST.