Code 39, Torque Converter Clutch Stuck In "Off" Position - LT. Truck: Notes

Fig 1: Code 39, TCC Circuit Diagram (Lt. Truck)

Courtesy of GENERAL MOTORS CORP.

The purpose of the automatic transmission Torque Converter Clutch (TCC) feature is to eliminate power loss of the torque converter stage when vehicle is in a cruise condition. This allows the convenience of the automatic transmission, and fuel economy of a manual transmission.

Fused battery ignition voltage is supplied to the TCC solenoid, which is used inside the valve body to shift a spool valve to modulate pressure to the TCC. This modulated pressure normally allows some slight slippage of TCC.

The PCM/TCM will engage TCC by grounding circuit No. 422, energizing the solenoid.

Code 39 will set under the following conditions:

• TCC is engaged.
• TCC "slip" is greater than 65 RPM for 2 seconds.
• 2nd or 3rd gear is selected or indicated.
  NOTE: Test numbers refer to test number on diagnostic chart.
  1. This test determines if transmission is receiving a TCC Command from the pass-thru connector. If bidirectional Scan tester is not available, TCC may be activated by grounding ALDL test terminal B with ignition on and engine off.
  2. This test checks for power to transmission.
  3. This test determines if PCM/TCM is commanding TCC to be on.