Automatic gearbox specialists
Having a gearbox speed sensor issue?
Limp mode, a speed-sensor code, or shifts that make no sense. A dead sensor will not come back after a restart.
- A sensor code and limp mode together?
- Speedo or shift problems after a wiring knock?
- Quoted a gearbox when the scan points at a sensor?
Gearbox speed sensors tell the control unit how fast the shafts are turning. When one fails, the automatic goes into limp mode or shifts blindly. Sensor diagnosis is core work at Service4Service.
Clearing a speed-sensor code is not a repair. The limp usually returns as soon as you pull away.
8am - 5.30pm Mon-Fri
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What are gearbox speed sensors?
Input and output speed sensors read shaft speed inside the automatic gearbox. The transmission control unit compares them to decide when to shift and whether a clutch pack is slipping.
On a dual-clutch they sit with the mechatronic. Wiring, the sensor or the toothed wheel can all throw the same code.
A diagnostic check with live data is how we avoid replacing a gearbox for a plug.
A speed-sensor fault will put you in limp
Without a speed signal the computer cannot time a shift. It holds a gear and lights a lamp. Keep driving like that and you overheat the gear you are stuck in.
Speed sensor symptoms people search
If any of these sound like your car, do not wait for it to fail on the road.
Limp with a sensor code
Classic. Test the sensor and the wiring.
Harsh or late shifts
The computer is guessing shaft speed.
Speedo drop-out
Sometimes the same signal, depending on the car.
After undertray or impact damage
A knocked plug.
Intermittent, worse when hot
A failing sensor or a cracked solder.
Slip code with no slip feel
The computer thinks the shafts do not match.
How gearbox speed sensors work
A magnetic or Hall sensor reads a reluctor. The TCU needs a clean pattern. Metal from a failing gearbox bearing can wipe a sensor face.
limp mode is the usual result when the pattern vanishes.
The sensor reads shaft speed
The TCU times the shift.
The signal drops out
Codes and limp follow.
Keep driving in limp
Heat in one gear. It only gets worse.
Sensor work we do
We test live data, wiring and the sensor, then replace it if that is the fault. We will not sell a unit because a code said sensor and nobody looked.
- Live data versus wiring tests
- Sensor replacement when honest
- Reluctor and debris checks
- Adaptation if the control needs it
In limp with a sensor code?
That is a test, not a gearbox by default. That is automatic gearbox repair of the control side until proven otherwise. Call.
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.
You may crawl in limp. You should not treat that as a journey.
No. Wiring, the TCU and a damaged reluctor all mimic it.
Some units do. Some are plug and play. We check the car.
Yes. Pulley speed is how a CVT knows what it is doing.
No.
Because the fault is still there. Clearing is not a repair.
Related guides
Do not replace a gearbox for a speed-sensor code
If you are in limp with a sensor fault, tell us the codes. We will test the signal before anyone talks about a unit.
