Diagnostic Aids

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

Perform this test only when directed by QUICK TEST. To prevent replacing good components, be aware following non-EEC areas may be at fault:

Engine base condition (compression, valve timing, etc.).
Brakes.
Transmission fluid, friction elements and cooling.
Transfer case linkage or internal condition. This test is only intended to diagnose:
Harness circuits (4x4 LOW, TCIL and TCS).
Faulty PCM.

Fig 1: Identifying 4x4 Low Switch Circuit (Touch Drive Option)

Fig 2: Identifying 4x4 Low Switch Circuit (W/O Touch Drive Option)

1) Codes 633 & 691 Code 633 indicates 4x4 low selector lever is not in 4x2 or 4x4 HIGH position during KOEO SELF-TEST. Code 691 indicates 4x4 selector fault is set when KAM value for engine speed/vehicle speed disagrees with PCM logic regarding engine speed/vehicle speed verses TCS position. Possible causes for these faults are:

Faulty 4x4 Low switch or 4x4 selector lever position.
Transfer case damaged internally.
Wiring harness circuit open or grounded.
Faulty PCM.

If 4x4 low selector lever was in 4x2 or 4x4 HIGH position during KOEO SELF-TEST, go to step 4). If 4x4 low selector was not in 4x2 or 4x4 HIGH position, repeat KOEO SELF-TEST with lever in 4x2 or 4x4 HIGH position.

2) Codes 632 & 653 Codes 632 and 653 indicate TCS is not cycled between engine ID code and WOT check during KOER SELF-TEST. Possible causes for these faults are:

Faulty TCS or switch not cycled.
Wiring harness circuit open or grounded.
Faulty PCM.

Ensure TCS is cycled between engine ID code and WOT check during KOER SELF-TEST, and go to step 4).

3) Codes 631 & 623 Codes 631 and 623 indicate TCS light circuit fault during KOEO SELF-TEST. Possible causes for these faults are:

TCS bulb burned out.
Wiring harness circuit open or grounded.

Ensure TCS is cycled during KOEO SELF-TEST, and go to step 5).

4) Cycle 4x4 Or Overdrive Cancel Switch Turn ignition off. Disconnect 60-pin PCM connector. Inspect terminals and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Turn ignition on.

To check 4x4 LOW circuit, measure voltage between test pin No. 12 and test pins No. 40 and 60 at breakout box while cycling switch in and out of 4x4 low position.
To check TCS circuit, measure voltage between test pin No. 41 and test pins No. 40 and 60 at breakout box while cycling overdrive cancel switch.

On all models, if voltage cycles, replace PCM and repeat QUICK TEST. If voltage does not cycle, go to next step if diagnosing a trouble code or step 7) if diagnosing driveability symptom only.

5) Check Circuits For Short To Ground Turn ignition off. Leave PCM disconnected from breakout box. Disconnect switch connector. Inspect for damage and repair as necessary.

To check 4x4 LOW circuit, measure resistance between test pin No. 12 and test pins No. 40 and 60 at breakout box.
To check TCS circuit, measure resistance between test pin No. 41 and pins No. 40 and 60 at breakout box.

Also measure resistance between test pin No. 32 and pins No. 40 and 60 at breakout box. If all readings are more than 10,000 ohms, go to next step for Code 631 or 623, or step 8) for Code 633, 632, 633 or 691. If any reading is 10,000 ohms or less, repair short circuit. Repeat QUICK TEST. If code is still present, go to step 7).

6) Check Power Through TCIL Circuit Turn ignition off. Leave PCM disconnected from breakout box. Measure voltage between test pin No. 32 and test pins No. 40 and 60 at breakout box. If voltage is more than 10.5 volts, replace PCM and repeat QUICK TEST. If voltage is 10.5 volts or less, go to next step.

7) Check Output Driver Voltage Signal Leave PCM disconnected from breakout box. Turn ignition on.

To check 4x4 LOW circuit, disconnect switch. Connect DVOM positive lead to test pin No. 12 and negative lead to PWR GND terminal of breakout box.
To check TCIL circuit, connect DVOM positive lead to test pin No. 32 and negative lead to PWR GND terminal of breakout box.

On all models, if either voltage reading is less than 2 volts, check bulb and fuse. If bulb and fuse are okay, repair open circuit and repeat QUICK TEST. If all voltage readings are 2 volts or more, go to next step.

Fig 3: Identifying KEY POWER Terminal In Fuse Panel (3.0L)

Engine condition (compression, cam timing, valves, etc.).
Charging system or battery.
Transmission linkage, internal components or cooling.

This test is not intended to diagnose transmission. This test is intended to diagnose:

Wiring harness circuits (TCC, CCS, EPC, SS3/4, SS1, SS2, SS3, SIG RTN, EPC PWR and VPWR).
Faulty Powertrain Control Module (PCM).

CIRCUIT TEST TC ACRONYMS

Acronym	Definition
CCC	Converter Clutch Control
CCS	Coast Clutch Solenoid
EPC	Electronic Pressure Control
MCCC	Modulated Converter Clutch Control
SS	Shift Solenoid
TCC	Torque Converter Clutch

TEST PIN NO. 53 (TCC) WIRE COLOR IDENTIFICATION

Application	Wire Color
Aerostar	Purple/Yellow

Fig 4: Identifying A4LD Solenoid Circuits (3.0L)

A4LD DTC IDENTIFICATION

Application	PCM Pin No.	KOEO Code
TCC	14 Or 53	629
SS3/4	51 Or 52	566

TEST PIN NO. 37 & 57 WIRE COLOR IDENTIFICATION

Application	Wire Color
All Models	Red

1) OUTPUT STATE CHECK Code 621, 622, 626, 629, 641 or 652 indicates shift solenoid did not respond to PCM command. Code 566 or 629 indicate TCC or SS3/4-4/3 did not change state when requested by PCM. Possible causes for these faults are:

Faulty solenoid assembly.
Circuit open or grounded.
Faulty Powertrain Control Module (PCM).

To enter output state Diagnostic Test Mode (DTM), use only VOM or DVOM. DO NOT use scan tester. Turn ignition off. Disconnect cruise control servo wiring harness connector. Connect DVOM negative lead to STO terminal at Data Link Connector (DLC). Connect positive lead to positive battery terminal. Install a jumper wire between SIG RTN terminal and STI terminal at DLC. See Figure . 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 DTM. Depress and release throttle. If voltage increases, remain in output state DTM and go to next step. If voltage does not increase, depress throttle to WOT and release. If STO voltage goes high, go to next step. If STO voltage does not go high, leave test equipment connected and go to CIRCUIT TEST QC.

2) Check Solenoid Electrical Condition Turn ignition off. Disconnect transmission wiring harness connector. Inspect terminals and repair if damaged. Connect VOM or DVOM positive test lead to solenoid wiring harness connector VPWR terminal. Connect negative test lead to appropriate shift solenoid terminal at transmission wiring harness connector. Turn ignition on. Cycle solenoid output on and off by depressing and releasing throttle 3-5 times. If voltage output changes by 0.5 volt or more, fault is in transmission. If voltage output does not change by 0.5 volt or more, go to next step.

3) Check Solenoid & VPWR Circuit Continuity Turn ignition off. Leave transmission wiring harness disconnected. Disconnect 60-pin PCM connector. Inspect terminals and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between transmission wiring harness connector terminal and corresponding test terminal at breakout box. See appropriate DTC IDENTIFICATION table at beginning of this circuit test. Also measure resistance between breakout box test pins No. 37 and 57 and VPWR terminal at transmission wiring harness connector. If each resistance is less than 5 ohms, go to next step. If any resistance is 5 ohms or more, repair open circuit and repeat QUICK TEST.

4) Check Solenoid Circuit For Short To Power Or Ground Leave ignition off and PCM disconnected. Leave transmission wiring harness disconnected. Measure resistance between PCM output signal test pin and test pins No. 37 and 57 at breakout box. Measure resistance between PCM output signal test pin and pins No. 40, 46 and 60 at breakout box. Also measure resistance between PCM output signal test pin and chassis ground. If any resistance is less than 10,000 ohms, repair short circuit and repeat QUICK TEST. If each resistance is 10,000 ohms or more, check solenoids. If solenoids are okay, replace PCM and repeat QUICK TEST.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 4) to step 10). No test procedures have been omitted.

10) Code 624 Or 625: Check VPWR To Solenoid Code 624 indicates failure of EPC circuit. Code 625 indicates EPC driver failure. Possible causes for these faults are:

Faulty solenoid.
Circuit open or grounded.

Turn ignition off. Disconnect transmission wiring harness connector. Turn ignition on. Measure resistance between VPWR and EPC PWR terminal at transmission wiring harness connector and chassis/battery ground. If voltage is less than 10.5 volts, repair open circuit and repeat QUICK TEST. If voltage is 10.5 volts or more, go to next step.

11) Check Solenoid Signal & VPWR Circuit Continuity Turn ignition off. Disconnect 60-pin PCM connector. Inspect terminals and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between VPWR/EPC PWR terminal at transmission wiring harness connector breakout box test pins No. 37 and 57. Also measure resistance between test pin No. 38 at breakout box and EPC terminal at transmission 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.

12) Check Circuit For Short To Power Or Ground Leave ignition off and PCM disconnected. Leave transmission wiring harness connector disconnected. Measure resistance between test pins No. 37 and 57 and suspect solenoid test pin at breakout box. Also measure resistance between test pins No. 40, 46 and 60 and suspect solenoid test pin at breakout box. If any resistance is less than 10,000 ohms, repair short circuit and repeat QUICK TEST. If each resistance is 10,000 ohms or more, check solenoids. If solenoids are okay, replace PCM and repeat QUICK TEST.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 12) to step 20). No test procedures have been omitted.

20) Code 621, 622, 641 Or 643: Check Solenoid Resistance KOEO Code 621 (SS1), 622 (SS2), 641 (SS3) or 643 (TCC) indicate failure in shift solenoid circuit. Possible causes for these faults are:

Faulty shift solenoid.
Circuit open or grounded.
Faulty PCM.

Turn ignition off. Disconnect transmission wiring harness connector. Measure resistance between suspect shift solenoid at transmission wiring harness connector and chassis ground. If resistance is 13-27 ohms, go to next step. If resistance is not 13-27 ohms, go to step 25).

21) Check Shift Solenoid For Short To Power Turn ignition off. Disconnect transmission wiring harness connector. Disconnect 60-pin PCM connector. Inspect terminals, and repair if damaged. Turn ignition on. Measure voltage between suspect shift solenoid at transmission wiring harness connector and chassis ground. If voltage is more than 0.5 volt, repair short to power and repeat QUICK TEST. If voltage is 0.5 volt or less, go to next step.

22) Check Shift Solenoid For Short To Ground Turn ignition off. Leave transmission wiring harness connector disconnected. Measure resistance between suspect shift solenoid at transmission wiring harness connector and chassis ground. Also, measure resistance between suspect shift solenoid and other circuits at transmission wiring harness connector. If any resistance is less than 10,000 ohms, repair short circuit and repeat QUICK TEST. If all resistances are 10,000 ohms or more, go to next step.

23) Check Shift Solenoid Circuit Continuity Turn ignition off. Leave transmission wiring harness connector disconnected. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between suspect shift solenoid test pin at breakout box and suspect shift solenoid terminal at transmission 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.

24) Check Shift Solenoid For Short To Power In Transmission Leave ignition off and PCM disconnected. Reconnect transmission wiring harness connector. Turn ignition on. Measure voltage between test pin No. 60 and suspect shift solenoid test pin at breakout box. If voltage is 0.5 volt or more, repair solenoid for short to power. If voltage is less than 0.5 volt, replace PCM and repeat QUICK TEST.

25) Check Transmission Wiring Leave ignition off. Check transmission wiring harness circuits and connectors for breaks or corrosion in insulation. Check for open or grounded circuits. Repair or replace as necessary. If connectors and circuits are okay, replace suspect solenoid and repeat QUICK TEST.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 25) to step 30). No test procedures have been omitted.

30) Continuous Memory Codes 621, 622, 641 & 643 Continuous Memory Code 621 (SS1), 622 (SS2), 641 (SS3) or 643 (TCC) indicates a failure was detected in shift solenoid circuit during last 80 warm-up cycles. Possible causes for these faults are:

Faulty shift solenoid.
Circuit open or grounded.

Turn ignition off. Check shift solenoid circuit between PCM and transmission. Repair or replace as necessary. If circuits are okay, go to next step.

31) Check For Intermittent Short Or Open Turn ignition off. Disconnect 60-pin PCM connector. Inspect terminals and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Turn ignition on. Connect test light between test pin No. 37 and suspect shift solenoid test pin at breakout box. See IDENTIFYING SHIFT SOLENOID TEST CIRCUITS table. Test light should be at partial brightness. Observe test light while wiggling and bending shift solenoid circuit between transmission and PCM. An open or short to power will be indicated by light going off. A short to ground will be indicated by light getting brighter. Repeat procedure for all solenoids. If fault is indicated, isolate and repair as necessary. If no fault is indicated, go to next step.

IDENTIFYING SHIFT SOLENOID TEST CIRCUITS

Shift Solenoid	Test Pin No.
SS1	11
SS2	51
SS3	52
CCC	55

32) Check For Intermittent Short To Ground Leave ignition off and PCM disconnected. Disconnect transmission wiring harness connector. Turn ignition on. Connect test light between test pin No. 37 and suspect shift solenoid test pin at breakout box. Test light should be off. Observe test light while wiggling and bending shift solenoid circuit between transmission and PCM. A short to ground will be indicated by light turning on. Repeat procedure for all solenoids. If fault is indicated, isolate and repair as necessary. If no fault is indicated, problem is intermittent and cannot be duplicated at this time.