Engine Controls - Tests W/codes - Transmission: Specifications GMC Pickup C2500

CODE 39, TORQUE CONVERTER CLUTCH STUCK "OFF"

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.

1. TCC is engaged.
2. TCC "slip" is greater than 65 RPM for 2 seconds.
3. 2nd or 3rd gear is selected or indicated. NOTE: Test numbers refer to test numbers on diagnostic chart. 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. This test checks for power to transmission. This test determines if PCM/TCM is commanding TCC to be on.

TORQUE CONVERTER CLUTCH (TCC) CIRCUIT CHECK

The automatic transmission TCC eliminates power loss of 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 is supplied to the TCC solenoid, located inside valve body, to shift a spool valve in order to modulate pressure to the TCC. The PCM/TCM will engage TCC by grounding circuit No. 422 to energize the solenoid.

TCC will engage under the following conditions.

1. Vehicle speed is greater than 30 MPH (48 km/h).
2. Engine at normal operating temperature greater than 149°F (65°C).
3. Transmission at normal operating temperature of 195°F (91°C).
4. Throttle position sensor output is not changing, indicating a steady road speed.
5. Brake switch is closed.
6. 4th gear is indicated.
7. No codes are stored. NOTE: Test numbers refer to test numbers on diagnostic chart.

1. This step checks for a shorted internal transmission harness or TCC solenoid.
2. This step verifies power supply to the TCC solenoid.
3. This step checks circuit No. 422 for a short to ground.
4. This step checks PCM/TCM's ability to control the TCC solenoid. If bidirectional scan tester is not available, TCC may be activated by grounding ALDL test terminal "B" with ignition on and engine off.