Diagnostic Aids

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

Perform this test when instructed during QUICK TEST or if directed by other test procedures. This test is used to diagnose the following:

Throttle linkage.
Wiring harness circuits (IAC and VPWR).
Faulty Idle Air Control (IAC) valve.
Faulty throttle body.
Faulty Powertrain Control Module (PCM).

Fig 1: IAC Circuit & Connector Terminal ID (Ranger)

Fig 2: IAC Circuit & Connector Terminal ID (Windstar)

1) Perform KOER self-test. If DTC P0505 or P1507 is present, go to next step. If DTC P0505 or P1507 is not present, IAC system is okay and testing is complete.

2) DTC P0505 & P1507

DTC P0505 indicates that IAC system malfunction has been detected. DTC P1507 indicates that IAC system underspeed fault has been detected. Possible causes are as follows:

IAC circuit open or shorted to PWR.
VPWR circuit open.
Contaminated IAC valve assembly.
Damaged throttle body.
Faulty PCM.

Turn ignition off. Disconnect IAC solenoid. Turn ignition on. Measure voltage between VPWR terminal of IAC solenoid wiring harness connector and battery ground terminal. If voltage is 10.5 volts or more, go to next step. If voltage is less than 10.5 volts, repair open VPWR circuit and repeat QUICK TEST.

3) Check IAC Solenoid Resistance

Turn ignition off. Connect DVOM positive lead to VPWR terminal of IAC solenoid wiring harness connector. Connect DVOM negative lead to IAC terminal. If resistance is 6-13 ohms, go to next step. If resistance is not 6-13 ohms, replace IAC valve assembly and repeat QUICK TEST.

4) Check IAC Solenoid Internal Short To Case

Turn ignition off. Measure resistance between each wiring harness connector terminal and IAC housing. If resistance is 10,000 ohms or more, go to next step. If resistance is less than 10,000 ohms, replace IAC solenoid assembly and repeat QUICK TEST.

5) Check IAC Circuit Continuity

Leave ignition off. Disconnect PCM wiring harness connector. Inspect pins for damage and repair as necessary. Install EEC-V Breakout Box (014-000950), leaving PCM disconnected. Measure resistance between breakout box test pin No. 83 (IAC) and IAC terminal at IAC solenoid wiring harness connector. If resistance is 5 ohms or more, repair open circuit and repeat QUICK TEST. If resistance is less than 5 ohms, go to next step.

6) Check IAC Circuit For Short To Power

Turn ignition on. Measure voltage between breakout box test pin No. 83 (IAC) and chassis ground. If voltage is one volt or more, repair circuit short to power and repeat QUICK TEST. If voltage is less than one volt, go to next step.

7) Check IAC Circuit For Short To Ground

Turn ignition off. Measure resistance between test pin No. 83 (IAC) and test pins No. 51 and 103 (PWR GND) at breakout box. If resistance is more than 10,000 ohms, go to next step. If resistance is less than 10,000 ohms, repair circuit short to ground and repeat QUICK TEST.

8) Check IAC Signal From PCM

Leave ignition off. Connect PCM to breakout box. Connect IAC solenoid to wiring harness connector. Connect DVOM between test pin No. 83 (IAC) and test pin No. 51 (PWR GND) at breakout box. Start engine and slowly increase speed to 3000 RPM. If voltage is 3.0-11.5 volts, remove IAC solenoid and check throttle body. If throttle body is okay, replace IAC assembly and repeat QUICK TEST. If voltage is not 3.0-11.5 volts, replace PCM and repeat QUICK TEST.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 8) to step 10). No test procedures have been omitted.

10) DTC P1506

This code indicates that IAC system has reached overspeed malfunction. Possible causes are as follows:

IAC circuit short to ground.
IAC assembly stuck open.
Air intake leaks or restrictions.
Damaged throttle body.
Contaminated or damaged IAC valve assembly.
Faulty Powertrain Control Module (PCM).

Check entire system for vacuum leaks. Repair or replace as necessary. If no vacuum leaks are found, go to next step.

11) Check IAC Solenoid Function

Start engine and allow to idle. Ensure transmission is in Park or Neutral. Disconnect IAC solenoid wiring harness connector. If engine speed drops, go to next step. If engine speed does not drop, check throttle body for damage. If throttle body is okay, replace IAC solenoid and repeat QUICK TEST.

12) Check IAC Circuit For Short To Ground

Turn ignition off. Disconnect PCM wiring harness connector. Inspect pins for damage and repair as necessary. Install EEC-V Breakout Box (014-000950), leaving PCM disconnected. Measure resistance between test pin No. 83 (IAC) and test pins No. 51 and 103 (PWR GND) at breakout box. If resistance is more than 10,000 ohms, replace PCM and repeat QUICK TEST. If resistance is less than 10,000 ohms, repair circuit short to ground and repeat QUICK TEST.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 12) to step 15). No test procedures have been omitted.

15) DTC P1505: Check Inlet Air Supply

DTC P1505 indicates that IAC system has reached the adaptive learning limit. Possible causes are as follows:

Air intake leaks or restrictions.
Throttle body linkage binding.
Contaminated or damaged IAC valve assembly.
Damaged throttle body.

Inspect air intake system for leaks. Repair or replace as necessary. If air intake system is okay, go to next step.

16) Check Air Filter

Turn ignition off. Remove air filter and inspect for excessive dirt or contamination. Repair or replace as necessary and repeat QUICK TEST. If air filter is okay, go to next step.

17) Check Throttle Body

Leave ignition off. Disconnect accelerator cable and air cleaner tube from throttle body. Check cable and throttle body linkage for binding or interference. If faults are present, go to CIRCUIT TEST HU, step 3). If no faults are present, go to CIRCUIT TEST HU, step 8).

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 17) to step 20). No test procedures have been omitted.

20) Continuous Memory DTC P1506: Monitor IAC Duty Cycle -Connect scan tester to DLC. Turn ignition on. Access IAC PID and RPM PID. IAC duty cycle should be 20-45 percent. Observe IAC PID and RPM PID for indication of fault while wiggling and bending wiring harness between IAC solenoid and PCM. Fault will be indicated by sudden increase in engine speed and decrease in duty cycle. If any faults are found, isolate and repair as necessary. Repeat QUICK TEST. If no faults are found, problem cannot be duplicated at this time. Go to CIRCUIT TEST Z.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 20) to step 30). No test procedures have been omitted.

30) Continuous Memory DTC P1507: Monitor IAC Duty Cycle -Connect scan tester to DLC. Turn ignition on. Access IAC PID, RPM PID and TP PID. IAC duty cycle should be 20-45 percent. Observe IAC PID and RPM PID for indication of fault while wiggling and bending wiring harness between IAC solenoid and PCM. Fault will be indicated by sudden increase in engine speed and decrease in duty cycle. If any faults are found, isolate and repair as necessary. Repeat QUICK TEST. If no faults are found, problem cannot be duplicated at this time. Go to CIRCUIT TEST Z.