TE90 - Check Harness and Connectors

Continuous Memory Diagnostic Trouble Codes (DTC) 637 or 638 indicate that sometime during the last 80 warm-up cycles, a fault has been detected in Transmission Fluid Temperature (TFT) circuit.

Possible causes:
- Fluid levels not to specification.
- Intermittent open/short in harness.
- Intermittent fault in TFT sensor.

- Key "OFF".

- Disconnect Powertrain Control Module (PCM). Inspect for damaged or pushed out pins, corrosion, loose wires, etc. Service as necessary.

- Install breakout box and reconnect PCM.

- Connect Digital Volt/Ohm Meter (DVOM) between test pin 2 and test pin 46 at breakout box.

- DVOM on 20 volts scale.

- Key "ON", engine "OFF".

- Note TFT sensor voltage.

- Perform the following while observing DVOM for a TFT/SIG RTN fault indication (voltage should remain stable or change gradually. A short to ground will be indicated by a reading of zero volts, an open by a reading of five volts and a short to power by a reading of greater than five volts):

- Shake, wiggle and bend TFT and SIG RTN wires between transmission and PCM.

- Is a fault indicated?

Yes -- Isolate fault and service as necessary. Remove breakout box. Reconnect all components. Re-evaluate symptom.

No -- For further diagnosis using the EEC-IV monitor box or Scan Tool, refer to Normal Scan Data Values. If an EEC-IV monitor box or Scan Tool is not available, go to pinpoint test step TD22 to check the TFT circuits). TD22 - Road Test