Diagnostic Aids

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

• 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).

Fig 1: Identifying A4LD Solenoid Circuits (Aerostar)

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.

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.

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.

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.

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.