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 by QUICK TEST or if directed by other test procedures. To prevent replacing good components, check the following non-EEC components and systems:

Refrigerant charge.
Low ambient temperature (less than 45°F). This test is intended to diagnose:
Wiring harness circuits (ACON, VPWR, GND and ACD).
A/C relay.
Faulty PCM.

1) KOEO Code 559: Check Power To A/C Relay Code 559 indicates A/C relay input circuit fault. Possible causes are as follows:

Open or shorted circuit.
Damaged A/C relay.
Damaged PCM.

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

2) Check A/C Relay Turn ignition off. Disconnect A/C relay. Measure resistance between IGN RUN and ACON terminal at A/C relay. Resistance should be 50-100 ohms. Also, measure resistance between ACON and the following A/C relay terminals; B(+), POWER-TO-CLUTCH and ground. Resistance should be more than 10,000 ohms. If resistances are not as specified, replace A/C relay. Reconnect all components and repeat QUICK TEST. If resistances are as specified, go to next step.

3) Check ACON Circuit For Short To Power Turn ignition off. Disconnect A/C relay. 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. Turn ignition on. Measure voltage between test pin No. 54 at breakout box and chassis ground. If voltage is one volt or more, repair short to power. Remove breakout box, reconnect all components and repeat QUICK TEST. If voltage is less than one volt, go to next step.

4) Check ACON Circuit For Short To Ground Turn ignition off. Disconnect A/C relay. With breakout box installed and PCM disconnected, measure resistance between test pin No. 54 at breakout box and chassis ground. If resistance is 10,000 ohms or less, repair short to ground. Remove breakout box, reconnect all components and repeat QUICK TEST. If resistance is more than 10,000 ohms, go to next step.

5) Check ACON Circuit Continuity Turn ignition off. Disconnect A/C relay. With breakout box installed and PCM disconnected, measure resistance between test pin No. 54 at breakout box and ACON terminal at A/C relay wiring harness connector. If resistance is less than 5 ohms, replace PCM. Remove breakout box, reconnect all components and repeat QUICK TEST. If resistance is 5 ohms or more, repair open circuit. Remove breakout box, reconnect all components and repeat QUICK TEST.

6) KOEO Code 539: Check A/C Input Code 539 indicates A/C demand input to PCM was low, indicating A/C on, during KOEO SELF-TEST. Verify A/C is off. If A/C was on, repeat KOEO SELF-TEST. If Code 539 is repeated, turn ignition off. Disconnect refrigerant pressure switch. Measure resistance between chassis ground and A/C demand (Blue/Black wire) side of refrigerant pressure switch wiring harness connector. If resistance is 10,000 ohms or less, check for defective A/C demand. If A/C demand is okay, repair short to ground. Reconnect all components and check system operation. If resistance is more than 10,000 ohms, go to next step.

7) Check Refrigerant Pressure Switch Turn ignition off. Disconnect refrigerant pressure switch. Measure resistance between each terminal of switch and chassis ground. If either resistance is 10,000 ohms or less, replace switch. Reconnect all components and check system operation. If each resistance is more than 10,000 ohms, go to next step.

8) Check PCM-To-Refrigerant Pressure Switch Circuit For Short To Ground Turn ignition off. Disconnect refrigerant pressure switch. Disconnect PCM 60-pin connector and inspect for damaged pins, corrosion and loose wires. Repair as necessary. Measure resistance between chassis ground and PCM side of refrigerant pressure switch wiring harness connector. If resistance is 10,000 ohms or less, repair short to ground. Reconnect all components and check system operation. If resistance is more than 10,000 ohms, replace PCM. Reconnect all components and check system operation.