Signs of a faulty automatic transmission control unit:
General signs:
* Transmission related error codes appear.
* The “Check Engine” or “Service Engine Soon” light is flashing.
* Difficulty shifting gears.
* Gear slip.
*Transmission fluid leak.
Special features:
* Hesitation or jerking when shifting gears. This indicates the control unit is unable to operate the shift solenoids smoothly.
* Gear shift delay. This may be due to a faulty control unit that is unable to send signals to the solenoids in a timely manner.
* Stuck transmission. This occurs when the control unit is unable to release the solenoid and keeps the transmission in a fixed gear.
* Transmission fluid leaking around the control unit. This indicates physical damage to the control unit or its gaskets.
Electrical signs:
* Open or short circuit in the wiring harness. This may prevent the control unit from receiving necessary signals or sending output signals.
* Failure of switching solenoids. Although the shift solenoids are not part of the control unit, they are electrically connected to it. Faulty solenoids can cause the control unit to malfunction.
* Grounding problems. Improper grounding may cause electrical noise and interference that may interfere with the normal operation of the control unit.
Other signs:
* Uncontrolled vehicle movement. This may indicate a serious control unit problem that is affecting engine or brake control.
* Increased fuel consumption. A faulty control unit may not properly regulate traction or gear shifting, resulting in increased fuel consumption.