Throttle sensor signal too high.
P0123 — also written PO123, P 0123, 0123 — is the OBD-II code for tps high input. Same code, same fix: this page covers every spelling of it.
Basically, your engine's 'brain' thinks you've got your foot pinned to the floor even when you're idling. It’s a classic headache on high-mileage Vauxhalls and older Ford Transits where the wiring gets brittle.
P0123 is a sensors fault code, typically costing £80–£400 to put right in a UK garage.
What P0123 actually feels like to drive
- Car is stuck in 'Limp Mode' and won't rev past 2,500 RPM.
- Engine starts okay but refuses to respond when you mash the pedal.
- The 'Check Engine' or 'Spanner' light is glowing bright on the dash.
- Jerky gear changes on automatics because the gearbox doesn't know where the throttle is.
- Unpredictable surging or 'hunting' at idle while queued at the lights.
What causes P0123?
- TPS failure
- Wiring short to power
UK vehicles that throw P0123 most often
- Vauxhall Corsa D 1.2/1.4 (2006-2014) - Very common wiring loom chafe nearby the battery tray.
- Ford Transit 2.4 TDCi (2006-2012) - Connector pins corrode due to road salt.
- Peugeot 207 1.4 VTi (2007-2013) - Oil wicking into the harness from the solenoid.
- Honda Civic 1.8 i-VTEC (2006-2011) - TPS internal track wear.
- Volkswagen Golf Mk5 1.6 FSI - Throttle body motor/sensor internal failure.
How P0123 is fixed
- TPS replacement
- Wiring repair
The P0123 misdiagnosis that wastes money
I see folks throwing new throttle bodies or sensors at this immediately, but nine times out of ten on something like a Transit or an older Corsa, it’s a 'rub-through' in the loom. The 5V reference wire chafes against the engine block or a bracket and shorts out, sending the full battery voltage back to the ECU. If you just swan in and swap the sensor without checking the wiring integrity first, you’re just wasting £150 of the customer's money and the light will pop right back on within ten miles.
What a UK garage should charge for P0123
For a basic TPS sensor on a Japanese car, you're looking at £80-£120 fitted. However, on most modern Euro 5/6 stuff like a VW or Volvo, the sensor is built into the throttle body. A genuine Bosch or Pierburg unit will set you back £200-£300 plus an hour's labour (£60-£90). If it’s just a wiring repair, expect a 'minimum one hour' diagnostic fee. Don't go to a main dealer for this; they'll charge double that and try to sell you a whole new loom for £800.
P0123 repair cost in the UK
Most P0123 repairs land between £80–£400 including parts and labour. The spread is wide because the cheap fix (a sensor, a hose, a leak) and the expensive fix (a major component) throw the same code — which is why a proper diagnosis before parts are bought saves the most money.
Bob's tip on P0123
Ask the garage for a 'live data' sweep. With the engine off but ignition on, they should watch the throttle percentage on the tool while slowly pressing the pedal. If it jumps straight to 100% or 'flickers' at the top, it's the sensor. If it stays stuck at 100% regardless of pedal position, it's likely a short in the wiring. Don't let them 'guess' with parts; a five-minute multimeter test on the harness can save you a two-hour labour bill for a job that didn't need doing.
Can you drive with P0123?
Drivable.
Urgency: medium.