Diagnostic Aids

WARNING: This page is about a different car, the 1995 Ford Ranger. However, it is still accessible from the selected car via links, so may be relevant.

Perform this test when directed by QUICK TEST . This CIRCUIT TEST is intended to diagnose:

* ACP sensor.

* ACP wiring harness circuits (ACP, VREF and SIG RTN).

* Powertrain Control Module (PCM).

Fig 1: Identifying ACP Sensor Test Circuit & Connector Terminals

1) DTC P1461

This code indicates PCM has detected high voltage in ACP circuit. Possible causes for this code are:

* Faulty ACP sensor.

* Open or shorted circuit.

* Faulty Powertrain Control Module (PCM).

Turn ignition off. Connect scan tester to DLC. Turn ignition on. Access ACP PID. If ACP PID voltage is more than 4.9 volts, go to next step. If ACP PID voltage is 4.9 volts or less, fault is intermittent and cannot be duplicated at this time and testing is complete.

2) Check VREF & SIG RTN Circuit

Turn ignition off. Disconnect ACP sensor wiring harness connector. Turn ignition on. Measure voltage between SIG RTN and VREF connector terminals. If voltage is 4-6 volts, go to next step. If voltage is not 4-6 volts, VREF is out of range or SIG RTN is open. Go to CIRCUIT TEST C.

3) Leave ignition on and ACP sensor disconnected. If voltage between SIG RTN and VREF connector terminals is less than one volt, replace ACP sensor and repeat QUICK TEST . If voltage between SIG RTN and VREF connector terminals is one volt or more, go to next step.

4) Check ACP Circuit For Short To VREF

Turn ignition off. Leave ACP sensor disconnected. Disconnect scan tester from DLC. Disconnect PCM 104-pin connector. Inspect connector for damage and repair as necessary. Measure resistance between ACP terminal and VREF terminal at ACP connector. If resistance is 10,000 ohms or more, go to next step. If resistance is less than 10,000 ohms, repair ACP circuit short to VREF and repeat QUICK TEST .

5) Check ACP Circuit For Short To Power

Leave ACP sensor and PCM disconnected. Measure voltage between ACP terminal at ACP connector and chassis ground. If voltage is less than one volt, replace PCM and repeat QUICK TEST . If voltage is one volt or more, repair ACP circuit short to power and repeat QUICK TEST .

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 5) to step 10). No test procedures have been omitted.

10) DTC P1462

This code indicates PCM has detected low voltage in ACP circuit. Possible causes for this code are:

* Faulty ACP sensor.

* Open or shorted circuit.

* Faulty Powertrain Control Module (PCM).

Turn ignition off. Connect scan tester to DLC. Turn ignition on. Access ACP PID. If ACP PID voltage is less than .15 volt, go to next step. If ACP PID voltage is .15 volt or more, replace PCM and repeat QUICK TEST .

11) Check VREF Circuit At ACP Sensor

12) Turn ignition off. Leave ACP sensor disconnected. Connect scan tester to DLC. Connect jumper wire between ACP terminal and VREF terminal at sensor connector. Turn ignition on. Access ACP PID (if scan tester cannot access ACP PID, go to next step). If ACP PID voltage is less than 4 volts, go to next step. If ACP PID voltage is 4 volts or more, replace ACP sensor and repeat QUICK TEST .

13) Check ACP Circuit For Short To Ground Or SIG RTN

Leave ignition off and ACP sensor disconnected. Disconnect scan tester from DLC. Disconnect PCM 104-pin connector. Inspect connector for damage and repair as necessary. Measure resistance between ACP terminal and SIG RTN terminal at ACP connector. Measure resistance between ACP terminal at ACP connector and negative battery terminal. If both resistance measurements are 10,000 ohms or more, go to next step. If either resistance measurements are less than 10,000 ohms, repair short circuit and repeat QUICK TEST .

14) Check ACP Circuit Continuity

Leave ignition off. Install EEC-V Breakout Box (014-000950), leaving PCM disconnected. Measure resistance between test pin No. 86 (ACP) at breakout box and ACP terminal at ACP sensor wiring harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in ACP circuit and repeat QUICK TEST .

15) Check A/C Clutch Engagement

Turn ignition on. Reconnect ACP sensor. Turn ignition on while listening for A/C clutch engagement. IfA/C clutch engages when ignition is turned on, replace PCM and repeat QUICK TEST . If A/C clutch engages when ignition is turned on, ensure system has correct refrigerant charge. Service A/C system if necessary. If A/C system has correct refrigerant charge, replace PCM and repeat QUICK TEST .

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 15) to step 18). No test procedures have been omitted.

18) Check Wiring Harness & Sensor

With scan tester connected, turn ignition on. Access ACP PID. While observing ACP PID, lightly tap on ACP sensor to simulate road shock. Wiggle sensor connector and wiring harness. A fault is indicated by a sudden change of voltage. If fault is indicated, isolate and repair as necessary. If no faults are indicated, go to CIRCUIT TEST Z.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 18) to step 20). No test procedures have been omitted.

20) DTC P1463

This code indicates PCM has detected that ACP sensor did not detect sufficient change in A/C system pressure when A/C switch was turned on. Possible causes for this code are as follows:

* A/C system mechanical malfunction.

* A/C system electrical malfunction (non-EEC related).

* A/C clutch continuous engagement.

* Faulty ACP sensor.

Turn A/C and defroster off. Start engine and allow to idle. Attempt to disengage A/C clutch. If A/C clutch disengages, go to next step. If A/C clutch does not disengage, repair or replace A/C compressor.

21) Check Power & Ground To A/C Clutch

Turn ignition off. Disconnect A/C cycling switch. Connect jumper wire between A/C cycling switch connector terminals. Disconnect A/C clutch. Connect voltmeter to A/C clutch connector terminals. Start engine and allow to idle. Turn A/C switch on. Monitor voltage for 15 seconds. Turn ignition off. If voltage is less than 10.5 volts, go to CIRCUIT TEST X, step 110). If voltage is 10.5 volts or more, replace ACP sensor and repeat QUICK TEST . If DTC 1463 is still present, fault is mechanical and EEC testing is complete.