Checking the control module
- Ignition off
- The breakout box connected
- Transmission control module (TCM) connected.
- Transmission connector disconnected
- Ignition on
- Gear selector in position P
- Activate and read off the status of solenoid S2.
Connect a voltmeter between terminals #B8 (#A68) and #A53 (#A53) while activating solenoid S2. The voltage must be approximately 0 V when the solenoid is not activated (OFF) and above 9 V when the solenoid is activated (ON).
The control module is OK if the voltage changes as above when the solenoid is activated/not activated. The control module is defective if the voltage does not change.
NOTE:If the system voltage is too low this may result in a low voltage value when solenoid S2 is activated. Check the system voltage and remedy as necessary.
NOTE:When removing the transmission connector, the control module may store diagnostic trouble codes (DTCs) for the gear-shift position sensor, the shift solenoids and the temperature sensor etc.
Other information:
- To disconnect the transmission connector, see Connecting the breakout box, GM automatic transmissions
- To replace the transmission control module (TCM), see Transmission control module (TCM), replacing
- For information about signals, see Signal specification .
Was the control module defective?
- YES
Refer to Verification
- NO
Refer to Checking the wiring and component