Automatic gearbox specialists
Having a transmission control unit issue?
Random limp mode, no shifts, or a TCU code. Clearing it is not a repair.
- Limp mode with a control-unit code?
- Shifts that vanished after a battery or jump start?
- Quoted a new gearbox when the computer may be the job?
The transmission control unit is the computer that times shifts. When it fails, the automatic goes into limp mode or will not select. TCU diagnosis is core automatic work at Service4Service.
A TCU code that returns after a clear is hardware or wiring until proven otherwise.
8am - 5.30pm Mon-Fri
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What is a transmission control unit?
A transmission control unit, or TCU, reads speed, load and temperature, then fires solenoid valves in the valve body. On a dual-clutch the mechatronic often includes this control.
It is not the engine ECU, though they talk. A speed sensor fault can look like a dead TCU. That is why we test before we quote a box.
adaptation values live here. After clutch or valve work the unit must relearn.
Limp mode from a TCU will not learn itself better
One gear, no kickdown, or a dead PRND display is the unit protecting the gearbox. Keep using it as normal and you can overheat what is left of Drive.
TCU symptoms people search
If any of these sound like your car, do not wait for it to fail on the road.
Stuck in one gear
Classic limp. Control or hydraulics.
No communication on scan
Power, earth, network or a dead unit.
After a battery change
Adaptations or a lost network. Diagnose, do not guess.
Random harsh shifts
Software, sensors or a failing board.
Mechatronic codes on a DSG
Control and hydraulics in one pack.
Will not adapt
Hardware underneath is still wrong.
How a TCU works
Sensors in, solenoid current out. Dirty automatic transmission fluid and heat cook the board on units mounted in the oil. Wiring faults do the same job from outside.
limp mode is the usual safety net when the computer no longer trusts a shift.
It reads speed and load
Then commands a solenoid.
A fault breaks that command
Limp, or no shift.
Clearing codes is not a repair
The fault returns. It only gets worse.
TCU work we do
We diagnose communication, sensor and internal control faults on conventional automatics and dual-clutch mechatronics, then repair or replace the control if that is honest.
- Scan and live-data diagnosis
- Wiring versus unit faults
- Mechatronic control on dual-clutch
- Adaptation after repair
Still in limp after a TCU code?
A stored control fault is the gearbox asking for a specialist. That is automatic gearbox repair. Call before you are left in one gear on the motorway.
Why this work comes to Service4Service
- Automatic and dual-clutch work is core work, not a sideline
- Diagnosis before parts
- Collection when the car should not be driven
- 12 months or 12,000 miles on parts and labour
Guarantee and payment
Repairs are backed by a 12 month or 12,000 mile warranty on parts and labour. See Payment Options for ways to pay.
Sometimes. Sometimes replacement and coding is honest. We test first.
Maps can help shift quality. A failed board or a wiring fault will not stay fixed with software.
On many dual-clutch units, yes, in the mechatronic. On some conventional autos it is external.
Usually yes.
No.
Crawl to safety and call. Do not treat one gear as a finished journey.
Related guides
Do not clear a TCU code and hope
If the auto is in limp or will not shift, tell us the codes. Control diagnosis is work we do every day.
