P0124
PowertrainThrottle Position Sensor/Switch A Circuit Intermittent
Most of the time this is a dodgy connection or chafed wiring at the throttle position sensor rather than the sensor itself dying. The ECU watches the voltage coming back from TPS circuit A, and when that signal drops out or jumps about for a split second rather than tracking smoothly with the pedal, it logs P0124 as an intermittent fault. The annoying part is the word intermittent. The signal often looks perfectly fine when you're stood in the garage testing it, then plays up the moment you're out on the road.
ⓘ Information only. This page provides general educational information about fault code P0124. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0124 mean?
P0124 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Throttle Position Sensor/Switch A Circuit Intermittent.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, sometimes flickering on and off rather than staying lit
- • Hesitation or a flat spot when you press the throttle, then it suddenly picks up
- • Throttle response feels erratic, hard to hold a steady speed on the motorway
- • Car drops into limp mode, often capping you at around 20mph until you restart
- • Lumpy idle that comes and goes
- • The odd stall when pulling away or coming to a stop
Possible causes
Causes commonly associated with P0124, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Damaged, chafed, or corroded wiring in the TPS circuit, this is the usual culprit with an intermittent code because the fault only shows when the wire flexes or warms up
- 2. Loose or corroded pins in the TPS connector, a quick unplug and inspect catches a lot of these
- 3. The throttle position sensor itself worn internally, the resistive track develops a dead spot that the wiper skips over
- 4. Carbon build-up on the throttle body throwing the readings off, common on direct-injection petrols
- 5. Faulty accelerator pedal position sensor on drive-by-wire setups, which feeds the same logic
- 6. Poor earth or a dropping reference voltage from the ECU side
- 7. ECU fault, rare, and only worth considering once everything else has been ruled out
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Hook up a scanner and watch live TPS voltage while you ease the throttle open by hand. A good signal sweeps smoothly from roughly 0.5V at idle to about 4.5V at full throttle. You're hunting for sudden drops to zero, spikes, or a flat dead spot mid-travel.
- 2. Unplug the connector and inspect both halves for green corrosion, spread pins, or oil ingress, then check the wiring for chafe points where the loom rubs against the bracket or bonnet hinge area
- 3. Wiggle test the harness and connector while the signal is on screen. If the voltage glitches when you flex a section of loom, you've found your intermittent.
- 4. Back-probe the connector with a multimeter and confirm you've got a steady 5V reference and a clean ground, anything sagging points to a supply problem rather than the sensor
- 5. If the wiring and supply are solid but the signal still drops out mid-sweep, the sensor's internal track is worn and it needs replacing
- 6. Throttle body fouled with carbon? Clean it and recheck before condemning anything, on some engines a sticky throttle plate skews the reading
Common questions about P0124
Should I just buy a cheap sensor off eBay or pay for the proper one? +
For a straight TPS, a decent aftermarket sensor from a known motor factor brand is usually fine and saves you a fair bit over the dealer part. Where I'd avoid the bargain-basement stuff is on drive-by-wire throttle bodies, where the cheap no-name sensors and pedal sensors are notorious for not matching the original calibration and tripping the same code back within weeks. If it's an integral electronic throttle body, the part is dear whichever way you go, so buy quality. And remember most P0124s are wiring, so don't throw a sensor at it before you've checked the loom.
Can I keep driving with this until I get it sorted? +
Short essential trips, maybe, but I wouldn't make a habit of it. Because the fault is intermittent you can get a sudden flat spot or a drop into limp mode without warning, and that's no fun pulling out of a junction or merging onto a motorway. If it's already stalling or dropping power, get it looked at before you drive it any distance.
Will this stop me getting through the MOT? +
The code on its own isn't a test item, but if the engine warning light is glowing when the tester looks at the dash, that's an automatic fail under the current MOT rules. Sort the underlying fault, then drive a few trips so the light clears before you book it in. If the light won't go out, the car isn't ready for the test.
What's it likely to cost to fix properly? +
A wiring repair is the cheap end, an hour or so of labour at an independent if they can find the chafe quickly, so figure £40 to £100. A sensor replacement at a local garage usually lands somewhere around £100 to £200 all in. An integral electronic throttle body is the painful one and can run several hundred pounds with the part. A main dealer will charge noticeably more on labour for the same job, so an independent who's happy to chase the wiring is your best value here.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →