Diagnostic Aids

WARNING: This page is about a different car, the 1995 Ford Pickup, 1995 Ford Econoline, 1995 Ford Club Wagon, and 1995 Ford Bronco. 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 the following non-EEC areas may be at fault:

Engine and/or transmission fluid level.
Engine and/or transmission fluid temperature.
Ambient temperature. This test is intended to diagnose:
TFT sensor.
Wiring harness circuits (TFT and SIG RTN).
Faulty Powertrain Control Module (PCM).

Fig 1: TFT Sensor Circuit At E4OD Transmission Connector ID (Bronco, "E" & "F" Series)

Fig 2: TFT Sensor Circuit At AODE & 4R70W Transmission Connector ID ("E" Series)

TFT SENSOR SPECIFICATIONS

Temperature: °F (°C)

⁽¹⁾ Volts

⁽¹⁾ Ohms

32 (0)

3.88

96,255

59 (15)

3.32

46,883

104 (40)

2.15

16,043

158 (60)

1.03

5260

194 (90)

0.60

2750

⁽¹⁾	Values may vary by 15 percent.

1) Code 636

KOEO Code 636 indicates TFT sensor is out of self-test range. Possible causes for these faults are:

Transmission fluid level incorrect.
Transmission fluid temperature incorrect.
Sensor resistance out of specification.
Faulty Powertrain Control Module (PCM).

Ensure transmission fluid temperature is more than 50°F (10°C). Repeat QUICK TEST. If Code 636 is present, go to next step. If Code 636 is not present, test is complete.

2) Check VREF At Throttle Position (TP) Sensor

Turn ignition off. Disconnect TP sensor wiring harness connector. Disconnect 60-pin PCM connector. Inspect terminals and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV). Connect PCM to breakout box. Turn ignition on. Measure voltage between VREF and SIG RTN terminals at TP sensor wiring harness connector. See Fig 3. If voltage is 4-6 volts, go to next step. If voltage is not 4-6 volts, go to CIRCUIT TEST C.

3) Check TFT Sensor Resistance

Turn ignition off. Disconnect PCM from breakout box. Allow transmission to cool. Measure and record resistance between test pin No. 46 and TFT test pin at breakout box. Drive vehicle until transmission fluid is at normal operating temperature. Disconnect PCM from breakout box. Measure resistance between test pin No. 46 and TFT test pin at breakout box. If cold resistance measurement is different than warm resistance measurement, and warm resistance is within specification, replace PCM and repeat QUICK TEST. If resistance is not as specified, replace TFT sensor.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 3) to step 10). No test procedures have been omitted.

10) KOEO Code 637

KOEO Code 637 indicates TFT sensor output exceeds self-test maximum voltage (4.8 volts). Possible causes for these faults are:

Transmission fluid level incorrect.
Open wiring harness circuit.
Faulty TFT sensor.
Faulty PCM.

Turn ignition off. Disconnect TFT wiring harness connector. Inspect terminals, and repair if damaged. Connect jumper wire between TFT and SIG RTN terminals. Perform KOEO SELF-TEST. If Code 638 is present, go to step 25). If Code 638 is not present, remove jumper wire and go to next step. If no codes are present, go to step 12).

11) Check TFT & SIG RTN Circuit Continuity

Turn ignition off. Leave TFT sensor 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 TFT circuit at TFT wiring harness connector and TFT test pin at breakout box. Also measure resistance between SIG RTN circuit at TFT wiring harness connector and test pin No. 46 at breakout box. If either 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.

12) Check TFT Sensor For Short To VPWR

Turn ignition off. Leave PCM and TFT sensor disconnected. Measure resistance between TFT test pin and test pins No. 37 and 57 at breakout box. If resistance is more than 10,000 ohms, replace PCM and repeat QUICK TEST. If resistance is 10,000 ohms or less, repair short circuit 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) KOEO Code 638

KOEO Code 638 indicates TFT sensor output is lower than self-test minimum voltage. Possible causes for these faults are:

Incorrect fluid level.
Damaged TFT sensor.
Shorted wiring harness circuit.
Faulty PCM.

Turn ignition off. Disconnect transmission wiring harness connector. Inspect terminals and repair if damaged. Perform KOEO SELF-TEST. If Code 637 is present, go to step 25). If Code 637 is not present, go to next step.

21) Check VREF At Throttle Position (TP) Sensor

Turn ignition off. Disconnect TP sensor wiring harness connector. Disconnect 60-pin PCM connector. Inspect terminals and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV). Connect PCM to breakout box. Turn ignition on. Measure voltage between VREF and SIG RTN terminals at TP sensor wiring harness connector. See Fig 3. If voltage is 4-6 volts, reconnect TP sensor and go to next step. If voltage is not 4-6 volts, go to CIRCUIT TEST C.

Fig 3: Throttle Position (TP) Sensor Connector Terminal ID (5.0L)

22) Check TFT Circuit For Short To Ground

Turn ignition off. Disconnect PCM from breakout box. Measure resistance between TFT test pin at breakout box and test pins No. 40, 46 and 60. If resistance is more than 10,000 ohms, replace PCM and repeat QUICK TEST. If resistance is 10,000 ohms or less, repair short circuit and repeat QUICK TEST.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 22) to step 25). No test procedures have been omitted.

25) Check Transmission Wiring Harness

Turn ignition off. Check transmission internal and external wiring and connectors for damage and corrosion. Repair or replace if necessary. If wiring is okay, replace TFT sensor and repeat QUICK TEST.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 25) to step 90). No test procedures have been omitted.

90) Continuous Memory Code 637 Or 638

Continuous Memory Code 637 or 638 indicates a fault has been detected in TFT circuit during previous 80 warm-up cycles. Possible causes for these faults are:

Incorrect fluid level.
Intermittent fault in TFT sensor.
Intermittent short or open in wiring harness.

Turn ignition off. Disconnect 60-pin PCM connector. Inspect terminals and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV). Connect PCM to breakout box. Connect DVOM between test pins No. 2 and 46 at breakout box. Turn ignition on. Shake and bend TFT and SIG RTN wires between transmission and PCM. Voltage should remain stable or change gradually. If voltage drops to zero, a short to ground is indicated. If voltage increases up to 5 volts, an open circuit is indicated. If voltage increases to more than 5 volts, a short to power is indicated. If fault is indicated, isolate and repair as necessary. If no faults are found, problem is intermittent and cannot be located at this time.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 90) to step 100). No test procedures have been omitted.

100) Continuous Memory Code 657

Continuous Memory Code 657 indicates excessive transmission temperatures. Possible causes for these faults are:

Damage in transmission cooling system.
Pulling overweight trailer.
Incorrect fluid level.
Damaged clutch.
Fault in TFT sensor.
Intermittent short or open in wiring harness.

Turn ignition off. Disconnect transmission wiring harness connector. Inspect terminals and repair if damaged. Perform KOEO SELF-TEST. If no codes are present, fault is in transmission. If Code 657 is present, check for fault causing transmission to overheat. If any other code(s) is present, service as necessary and repeat QUICK TEST.