TF90 - Complete Transmission Drive Cycle

Continuous Memory Diagnostic Trouble Code (DTC) 639 indicates that sometime during the last 40 or 80 warm-up cycles, the Powertrain Control Module (PCM) detected an error in the Turbine Shaft Speed Sensor (TSS) / Output Shaft Speed Sensor (OSS) output signal.

Possible causes:
- Transmission (internal components).
- Damaged TSS/OSS.
- Damaged harness circuits.
- Damaged PCM.

- Perform transmission Drive Cycle:
- Record and clear Continuous Memory DTCs. Quick Test Appendix (Detailed Testing Instructions)
- Warm engine to operating temperature.
- Place gear selector in "Drive".
- Obey all local traffic laws. Accelerate heavily to 35 mph.
- Return to idle.
- Shut the engine off.
- After drive cycle is completed, run Key On Engine Off Self-Test and record Continuous Memory DTCs displayed.

- Did Continuous Memory DTC 639 repeat?

Yes -- Go to TF91. TF91 - Check TSS/OSS Circuit Continuity

No -- Unable to duplicate and/or identify fault at this time. For further diagnosis using the EEC-IV monitor box or Scan Tool, refer to Normal Scan Data Values. For all others, clear continuous memory. Clearing Diagnostic Trouble Codes