P0108
PowertrainManifold Absolute Pressure/Barometric Pressure Circuit High Input
You'll usually notice this as a warning light along with the engine feeling flat and hesitant, sometimes a rough idle that won't settle. On a turbo or supercharged car the power can drop off and it may slip into limp mode to protect the engine. What's behind it is the MAP sensor signal reading higher than the ECU expects. The sensor measures pressure in the intake, and when its voltage stays pinned high the ECU stops trusting it and flags P0108.
ⓘ Information only. This page provides general educational information about fault code P0108. 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 P0108 mean?
P0108 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Manifold Absolute Pressure/Barometric Pressure Circuit High Input.
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, often with a flat, gutless feel under acceleration
- • Rough or lumpy idle, worst just after a cold start
- • Noticeable loss of boost and power on turbo cars, sometimes dropping into limp mode
- • Fuel economy goes the wrong way, you're filling up more often
- • Hesitation or a flat spot when you put your foot down
- • Occasional stalling at idle or hard starting when hot
Possible causes
Causes commonly associated with P0108, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. MAP sensor itself failed or reading high. The most common cause, and on boosted engines they take a hammering from heat and pressure cycles
- 2. Corroded or loose connector at the sensor, water and road salt get into the plug and push the signal high
- 3. Damaged signal wire shorting to a voltage feed in the harness, which forces the reading up artificially
- 4. Boost or vacuum leak around the intake, hoses or gaskets giving the sensor a false pressure picture
- 5. A split or popped-off vacuum hose to the sensor on manifold-mounted setups
- 6. ECM supplying a wrong reference voltage, rare but it happens after water ingress or a previous bodged repair
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 live data and watch the MAP voltage. Key on, engine off it should sit near barometric pressure around 4.5 to 5V, then drop to roughly 1 to 1.5V at idle. A signal stuck high points straight at the fault
- 2. Unplug the connector and check it properly. Look for green corrosion, damp, bent or spread pins, and give it a wiggle test with the engine running
- 3. Walk the intake for boost and vacuum leaks. On turbo cars check the charge pipes and intercooler hoses, a popped boost pipe will throw the readings out
- 4. Back-probe the sensor's earth and reference wires against the ECM with a multimeter, you're looking for a short to power or a broken earth
- 5. If the voltage stays high with the sensor unplugged, the fault is in the harness or the ECM, so isolate the signal wire at the module to narrow it down
Common questions about P0108
Can I just buy a cheap MAP sensor off eBay, or do I need a genuine one? +
For a daily driver, a quality aftermarket sensor from a known brand like Bosch or Delphi is fine and saves you money over the dealer part. Where I'd be careful is the no-name £8 specials, the calibration can be off and you'll be chasing the same fault a fortnight later. On a turbo car especially, the MAP reading feeds straight into boost control, so a wrong-curve cheap sensor can leave the car running poorly even with no light. Spend a little more, fit a branded unit, and don't waste the labour twice.
Is it alright to keep driving like this for a bit? +
Short trips to get it looked at, probably. Long term, no. The ECU is working off a bad pressure reading, so it's getting the fuelling wrong, which can foul plugs and load the catalytic converter with unburnt fuel over time. On a turbo engine a false high MAP signal can also have it pulling boost or sitting in limp mode, which is no fun on the motorway. Sort it sooner rather than later.
Will this stop me passing the MOT? +
The code on its own isn't a fail, but if the engine warning light is lit when the tester plugs in, that's an automatic fail on the MIL check. So you can't just clear it and drive straight to the test, the light will come back once the fault is still present. Fix the cause first, drive a few cycles to confirm the light stays off, then book it in.
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 →