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Diagnostic Aids

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

  1. 1) DTC P1461

    This DTC indicates PCM has detected high voltage in ACP circuit. Possible causes for this fault are:
    • Faulty ACP Sensor
    • Open Or Shorted Circuit
    • Faulty Powertrain Control Module (PCM)

    Turn ignition switch to ON position. Using scan tool, select ACP V PID from PID/DATA MONITOR & RECORD menu. If PID voltage is 4.9 volts or more, go to next step. If PID voltage is less than 4.9 volts, fault is intermittent. Go to step  18).

  2. 2) Check VREF & SIG RTN Circuit

    Turn ignition switch to OFF position. Disconnect ACP sensor connector. Turn ignition switch to ON position. Measure voltage between SIG RTN and VREF terminals at ACP sensor harness connector. See Fig 1. 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 circuit is open. Go to TEST C .
    Fig 1: Identifying ACP Sensor Circuits & Connector Terminals
    G00013263Courtesy of FORD MOTOR CO.

  3. 3) Induce Opposite Signal

    Turn ignition switch to ON position. Using scan tool, select ACP V PID from PID/DATA MONITOR & RECORD menu. If PID voltage is 4.9 volts or more, go to next step. If PID voltage is less than 4.9 volts, replace ACP sensor. Start engine and turn A/C on for 15 seconds. Turn A/C off and repeat QUICK TEST .

  4. 4) Check ACP Circuit For Short To VREF

    Turn ignition switch to OFF position. Disconnect scan tool from Data Link Connector (DLC). Disconnect PCM connector(s). Measure resistance between ACP and VREF terminals at ACP sensor harness connector. If resistance is more than 10 k/ohms, go to next step. If resistance is 10 k/ohms or less, repair ACP circuit short to VREF. Start engine and turn A/C on for 15 seconds. Turn A/C off and repeat QUICK TEST .

  5. 5) Check ACP Circuit For Short To Power

    Turn ignition switch to ON position. Measure voltage between ACP terminal at ACP sensor harness connector and chassis ground. If voltage is less than one volt, go to next step (Escort and LS) or replace PCM (except Escort and LS). If voltage is one volt or more, repair ACP circuit short to power. Start engine and turn A/C on for 15 seconds. Turn A/C off and repeat QUICK TEST .

  6. 6) Check Circuit Resistance

    Turn ignition switch to OFF position. Leave ACP sensor disconnected. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. On LS, measure resistance between PCM connector terminal A42 (ACP) and ACP terminal at ACP sensor harness connector. On all other models, measure resistance between PCM connector terminal No. 86 (ACP) and ACP terminal at ACP sensor harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit. Start engine and turn A/C on for 15 seconds. Turn A/C off and repeat QUICK TEST .

  7. 7) Check PCM

    Reconnect PCM connector. Leave ACP sensor disconnected. On LS, connect a jumper wire between PCM connector terminals No. A42 and A17 (SIG RTN). On all other models, connect a jumper wire between PCM connector terminals No. 86 and 91 (SIG RTN). Turn ignition switch to ON position. Using scan tool, select ACP V PID from PID/DATA MONITOR & RECORD menu. If PID voltage is less than 4.9 volts, replace ACP sensor. Start engine and turn A/C on for 15 seconds. Turn A/C off and repeat QUICK TEST . If PID voltage is 4.9 volts or more or if scan tool is now unable to communicate, replace PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Program PCM. See FLASH VEHICLE IDENTIFICATION BLOCK PROCEDURE . Start engine and turn A/C on for 15 seconds. Turn A/C off and repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 7) to step 10). No test procedures have been omitted.

  8. 10) DTC P1462: Check ACP Voltage PID

    This DTC indicates PCM has detected low voltage in ACP circuit. Possible causes for this fault are:
    • Faulty ACP Sensor
    • Open Or Shorted Circuit
    • Faulty Powertrain Control Module (PCM)

    Turn ignition switch to ON position. Using scan tool select ACP V PID. If PID voltage is .15 volt or less, go to next step. If PID voltage is more than .15 volt, fault is intermittent. Go to step  18).

  9. 11) Check VREF Circuit At ACP Sensor

    Turn ignition switch to OFF position. Disconnect ACP sensor connector. Turn ignition switch to ON position. Measure voltage between SIG RTN and VREF terminals at ACP sensor harness connector. See Fig 1. If voltage is 4-6 volts, go to next step. If voltage is not 4-6 volts, VREF is out of range. Go to TEST C .

  10. 12) Induce Opposite Signal

    Turn ignition switch to OFF position. Connect a jumper wire between ACP and VREF terminals at ACP sensor harness connector. Turn ignition switch to ON position. Using scan tool, select ACP V PID from PID/DATA MONITOR & RECORD menu.
    NOTE: If communication link error is displayed, remove jumper wire and go to next step.

    If PID voltage is 4 volts or less, go to next step. If PID voltage is more than 4 volts, replace ACP sensor. Start engine and turn A/C on for 15 seconds. Turn A/C off and repeat QUICK TEST .

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

    Turn ignition switch to OFF position. Disconnect scan tool from Data Link Connector (DLC). Disconnect PCM connector(s). Measure resistance between ACP and SIG RTN terminals at ACP sensor harness connector. Measure resistance between ACP terminal at ACP sensor harness connector and negative battery terminal. If both resistance readings are more than 10 k/ohms, go to next step. If any resistance reading is 10 k/ohms or less, repair short circuit. Start engine and turn A/C on for 15 seconds. Turn A/C off and repeat QUICK TEST .

  12. 14) Check ACP Circuit Resistance

    On LS, measure resistance between PCM connector terminal A42 (ACP) and ACP terminal at ACP sensor harness connector. On all other models, measure resistance between PCM connector terminal No. 86 (ACP) and ACP terminal at ACP sensor 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. Start engine and turn A/C on for 15 seconds. Turn A/C off and repeat QUICK TEST .

  13. 15) Check A/C Clutch Engagement

    Turn ignition switch to ON position. Reconnect ACP sensor. Turn A/C switch on while listening for A/C clutch engagement. If A/C clutch engages when A/C switch is turned on, replace PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Program PCM. See FLASH VEHICLE IDENTIFICATION BLOCK PROCEDURE . Start engine and turn A/C on for 15 seconds. Turn A/C off and repeat QUICK TEST . If A/C clutch does not engage when ignition is turned on, go to next step.

  14. 16) Check Refrigerant Charge

    Reconnect all components. Connect A/C manifold gauge set and check if A/C system has correct refrigerant charge. Service A/C system as necessary. Start engine and turn A/C on for 15 seconds. Turn A/C off and repeat QUICK TEST . If A/C system has correct refrigerant charge, replace PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Program PCM. See FLASH VEHICLE IDENTIFICATION BLOCK PROCEDURE . Start engine and turn A/C on for 15 seconds. Turn A/C off and repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 16) to step 18). No test procedures have been omitted.

  15. 18) Check Wiring Harness & Sensor

    Turn ignition switch to ON position. Using scan tool, select ACP V PID from PID/DATA MONITOR & RECORD menu. While observing ACP V 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 PID voltage. If fault is indicated, isolate and repair as necessary. Start engine and turn A/C on for 15 seconds. Turn A/C off and repeat QUICK TEST . If no faults are indicated, unable to duplicate fault at this time. Go to 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.

  16. 20) DTC P1463: Verify A/C Clutch Can Disengage

    This DTC 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 fault are:
    • A/C System Mechanical Malfunction
    • A/C System Electrical Malfunction (Non-EEC Related)
    • A/C Clutch Continuous Engagement
    • ACP Or VREF Open Circuit
    • Faulty ACP Sensor

    Turn A/C and defroster off. Start engine and allow to idle. Verify A/C clutch disengages. If A/C clutch disengaged, go to next step. If A/C clutch did not disengage, check A/C clutch circuit. See CLIMATE CONTROL (A/C ALWAYS ON) in TROUBLE SHOOTING - NO CODES - EEC-V (GASOLINE) article. Repair as necessary.

  17. 21) Check Power & Ground To A/C Clutch

    Turn ignition switch to OFF position. Disconnect A/C cycling switch. Connect a jumper wire between A/C cycling switch connector terminals. Disconnect A/C clutch. Connect non-powered test light between power and ground terminals at A/C clutch harness connector. Start engine and allow to idle. Turn A/C switch on. Monitor test light for 15 seconds. If test light comes on or A/C clutch can be heard clicking, go to next step. If test light does not come on or A/C clutch cannot be heard clicking, see appropriate A/C HEATER SYSTEMS article in AIR CONDITIONING & HEATING.

  18. 22) Check ACP V PID

    Start engine. Ensure A/C is off. Using scan tool, access ACP V PID from PID/DATA MONITOR & RECORD menu. Note A/C V PID voltage reading. Monitor PID value and turn A/C on. Note PID voltage reading within 5 seconds of A/C clutch engagement and compare reading with PID reading noted previously. If PID voltage change is more than .3 volt, ACP sensor and PCM can detect change in A/C pressure. Check A/C system for proper operation and repair as necessary. If PID voltage change is .3 volt or less, go to next step.

  19. 23) Check Refrigerant Charge

    Turn ignition switch to OFF position. Reconnect all components. Connect A/C manifold gauge set. With A/C off, note high pressure reading. Turn A/C on and within 5 seconds, note high pressure reading. If high pressure reading changes more than 30 psi (207 kPa), go to next step. If high pressure reading does not change more than 30 psi (207 kPa), service A/C system as necessary. Start engine and turn A/C on for 15 seconds. Turn A/C off and repeat QUICK TEST .

  20. 24) Check VREF Circuit At ACP Sensor

    Turn ignition switch to OFF position. Disconnect ACP sensor connector. Turn ignition switch to ON position. Measure voltage between SIG RTN and VREF terminals at ACP sensor harness connector. If voltage is 4-6 volts, go to next step. If voltage is not 4-6 volts, VREF is out of range. Go to TEST C .

  21. 25) Check ACP Circuit Resistance

    Turn ignition switch to OFF position. Disconnect PCM connector(s). On LS, measure resistance between PCM connector terminal A42 (ACP) and ACP terminal at ACP sensor harness connector. On all other models, measure resistance between PCM connector terminal No. 86 (ACP) and ACP terminal at ACP sensor harness connector. If resistance is less than 5 ohms, replace ACP sensor. Start engine and turn A/C on for 15 seconds. Turn A/C off and repeat QUICK TEST . If resistance is 5 ohms or more, repair open in ACP circuit. Start engine and turn A/C on for 15 seconds. Turn A/C off and repeat QUICK TEST .
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