Diagnostic Aids

WARNING: This page is about a different car, the 1995 Ford Explorer and 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. This test is intended to diagnose:

Wiring harness circuit (OSS).
Faulty Powertrain Control Module (PCM).

Fig 1: Turbine Shaft Speed (TSS) Sensor Circuit (Explorer)

TEST PIN NO. 5 (OSS+/TSS+) WIRE COLOR IDENTIFICATION

Application	Wire Color
All Models	Dark Green/White

1) KOER Code 639 KOER Code 639 indicates input from OSS/TSS sensor to PCM is out of calibration. Possible causes for this fault are:

Faulty OSS/TSS sensor.
Circuit open or grounded.
Faulty Powertrain Control Module (PCM).

Turn ignition off. Disconnect OSS/TSS sensor wiring harness connector. 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 OSS+/TSS+ terminal at OSS/TSS sensor wiring harness connector and test pin No. 5 at breakout box. Also measure resistance between SIG RTN terminal at OSS wiring harness connector and test pin No. 46 at breakout box. If any resistance is more than 5 ohms, repair open circuit and repeat QUICK TEST. If each resistance is 5 ohms or less, go to next step

2) Check Circuit For Short To Power Or Ground Leave ignition off and OSS/TSS disconnected. Measure resistance between test pin No. 5 and test pins No. 37 and 57 at breakout box. Measure resistance between test pin No. 5 and test pins No. 40, 46 and 60 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, go to next step.

3) Measure OSS/TSS Sensor Resistance Leave ignition off and OSS/TSS disconnected. Measure resistance between sensor terminals. Resistance should be 450-750 ohms (AODE/4R70W transmission) or 64-120 ohms (4R55E transmission) . If resistance is not as specified, replace OSS/TSS sensor and repeat QUICK TEST. If resistance is as specified, check internal transmission components. If okay, replace PCM and repeat QUICK TEST.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 3) to step 90). No test procedures have been omitted.

90) Continuous Memory Code 639 Code 639 indicates PCM detected incorrect output signal from OSS/TSS sensor during previous 40-80 warm-up cycles. Possible causes for this fault are:

Faulty OSS/TSS sensor.
Faulty transmission.
Circuit open or grounded.
Faulty PCM.

Record and clear continuous memory codes. While test driving vehicle, stop, ensure transmission gear selector is in Drive, and accelerate heavily to 35 MPH. After test drive, perform KOEO SELF-TEST and record all codes. If Continuous Memory Code 639 does not repeat, problem cannot be duplicated at this time. If Continuous Memory Code 639 is repeated, go to next step.

91) Check OSS/TSS 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. Disconnect OSS/TSS wiring harness connector. Measure resistance between OSS/TSS terminal at OSS/TSS sensor connector and test pin No. 5 at breakout box. Also measure resistance at SIG RTN terminal at OSS/TSS connector and test pin No. 46 at breakout box. If any resistance is more than 5 ohms, repair short circuit and repeat QUICK TEST. If each resistance is 5 ohms or less, go to next step.

92) Check Circuit For Short To Power Or Ground Turn ignition off. Leave OSS/TSS sensor disconnected. Measure resistance between test pin No. 5 and test pins No. 37 and 57 at breakout box. Also measure resistance between test pin No. 5 and test pins No. 40, 46 and 60 at breakout box. If any resistance is less than 500 ohms, repair short circuit and repeat step 90) to verify code elimination. If each resistance is 500 ohms or more, go to next step.

93) Measure Sensor Resistance Turn ignition off. Leave sensor disconnected. Measure resistance between sensor terminals. Resistance should be 450-750 ohms (AODE/4R70W transmission) or 64-120 ohms (4R55E transmission). If resistance is as specified, replace PCM and repeat step 90) to verify code elimination. If resistance is not as specified, replace OSS/TSS sensor and repeat step 90) to verify code elimination.