P0229
PowertrainThrottle Position Sensor/Switch C Circuit Intermittent
Most of the time this comes down to a dodgy connection or chafed wiring in the throttle or accelerator pedal sensor circuit rather than a dead sensor. The ECM watches the 'C' signal coming back from the throttle position sensor or pedal assembly, and when that signal flickers or drops out for a split second, it logs P0229. Because it's an intermittent fault, the car might behave perfectly for days and then suddenly throw a wobbly. That on-off nature is exactly what makes it a pain to pin down.
ⓘ Information only. This page provides general educational information about fault code P0229. 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 P0229 mean?
P0229 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Throttle Position Sensor/Switch C 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, sometimes coming and going with the fault
- • Hesitation or a flat spot when you put your foot down
- • Car dropping into limp mode with power cut right back, often capped around 20-30 mph
- • Sudden power loss or the revs dipping when you didn't lift off
- • Harder starting, more noticeable from cold
- • Black smoke from the exhaust on start-up if fuelling has gone off
Possible causes
Causes commonly associated with P0229, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Corroded, loose, or backed-out pins at the throttle body or pedal connector, the usual offender with an intermittent code like this
- 2. Chafed, pinched, or broken wiring in the 'C' circuit harness, often where the loom flexes near the pedal or runs along the bulkhead
- 3. A throttle position sensor that's worn internally and dropping out at certain angles
- 4. Accelerator pedal position sensor on its way out, common on drive-by-wire setups
- 5. Poor earth on the sensor ground circuit causing the voltage to wander
- 6. Carbon build-up binding the throttle plate so the sensor reads erratically
- 7. Faulty ECM or corrupted calibration, rare, and only after everything else checks 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. Read the freeze-frame data for the conditions when the code logged, then wiggle-test the connectors and harness at the pedal and throttle body while watching live data. An intermittent fault usually shows itself when you flex the wiring
- 2. Inspect every pin and connector at the throttle and pedal assembly for green corrosion, spread terminals, or a loose lock. This is where most of these live
- 3. Watch the 'C' circuit voltage on a scan tool as you slowly sweep the throttle. You're hunting for a glitch or dropout, not a steady reading. A healthy sensor should climb smoothly, roughly 0.5V closed up to about 4.5V at full throttle
- 4. Back up the scan tool with a multimeter on the signal, supply, and ground wires, checking for voltage drop under load. A bad earth shows up here that the scanner can miss
- 5. Check the throttle body for carbon and any sticking in the bore that could be upsetting the sensor
- 6. If wiring, connectors, and the sensor all test clean, check for any TSBs on your model before condemning the ECM. Plenty of intermittent faults have a known fix
Common questions about P0229
Can I keep driving it for now? +
Short hops are usually fine, but I wouldn't rely on it for a motorway run or anything time-critical. The trouble with an intermittent fault is it can drop you into limp mode without warning, and having the power suddenly cut on a busy roundabout is no fun. If it's already limping or losing power unpredictably, get it looked at before you drive it far.
Is this going to cost me the MOT? +
The code on its own isn't tested, but the tester will check whether the engine warning light is on. If the MIL is lit when you bring it in, that goes down as a fail on the warning lamp check. Fix the underlying fault, clear the light, and make sure it stays off over a few drive cycles before you book the test.
What am I looking at to put it right? +
Depends entirely on what's behind it. A connector clean-up or a wiring repair might be £40 to £120 at an independent. A throttle position sensor or pedal sensor is usually a couple of hundred quid fitted, more at a main dealer who'll often charge for the genuine part plus a coding job. If it actually turns out to be the ECM, you're into four figures with programming. Get a couple of quotes, and make sure they've diagnosed it properly rather than guessing at a sensor.
How do I work out which cause it actually is on my car? +
Start with the wiggle-test, because if flexing a connector or section of loom makes the fault appear or clear, you've found it without spending a penny on parts. If the wiring stays solid but the live voltage glitches as you move the throttle, the sensor itself is the suspect. If everything reads clean and steady but the car still hesitates, look at the throttle body for carbon binding. The ECM comes last, only once you've ruled out the cheap stuff, because it's the most expensive and the least likely.
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 →