P0108: The MAP sensor voltage is too high
Manifold Absolute Pressure/Barometric Pressure Circuit High Input
The manifold pressure (MAP) sensor signal is too high, so the engine may run rich and harm the catalytic converter. Get it checked within a few days. If it runs rough or stalls, stop driving.
Stop driving and get help if
- The check engine light is flashing
- The temperature gauge runs high, or you see steam (overheating)
- The car loses power, hesitates badly or stalls
- You smell burning or see smoke
- A brake warning light comes on, or the brakes feel different
Pull over as soon as you can, turn the engine off, and call a tow or roadside help.
What it means
The MAP sensor output voltage is above the maximum the ECM accepts. When the MAP signal reads too high, the computer thinks manifold pressure is very high (low vacuum), which it interprets as high engine load. It responds by delivering excess fuel, causing a rich condition. A MAP sensor stuck at or near 5V almost always means an internal open circuit in the sensor or a short to the 5V reference line in the wiring.
Common causes
- Failed MAP sensor with internal open circuitAn open sensor output floats up toward the 5V reference, triggering the high-input code.
- Short to 5V reference in the MAP signal wiringA chafed signal wire touching the reference wire holds the signal high regardless of actual pressure.
- Damaged connector causing signal-to-power crossMelted or pushed pins inside the connector can bridge the signal pin to the 5V supply pin.
- ECM input circuit faultRare, but a damaged ECM pin can read the MAP signal as high. Only consider after ruling out sensor and wiring.
What the fix could involve
From the cheaper fix to the bigger one. Prices depend on your car, your area and the shop, so ask for a written quote that names the part and the labor before you approve it.
- MAP sensor replacement
- Wiring repair
Symptoms
- Check engine light on
- Rich running, fuel smell from exhaust
- Black smoke from tailpipe
- Rough idle from over-fueling
- Poor fuel economy
- Possible misfires from excess fuel
What to do next
Disconnect the MAP sensor and read the voltage on the signal wire with the ignition on. If it drops to near zero when unplugged, the sensor is shorted internally or the wiring has a short to the reference line. Replace the sensor and retest. If signal voltage stays high with the sensor unplugged, the problem is in the wiring between the sensor and ECM.
Lewis reads P0108 alongside any related MAP and vacuum codes, and Lewis Pro explains whether the sensor or a vacuum problem is the more likely cause on your engine. Get Lewis on the App Store or Google Play.
Related codes
FAQ
- Can a disconnected vacuum hose cause P0108?
- Yes and no. A disconnected vacuum hose exposes the MAP sensor port to atmospheric pressure, which reads as very low vacuum (high pressure). This can push the reading high on some sensors. Check the vacuum line before replacing the sensor.
- Will P0108 damage my catalytic converter?
- If the engine runs rich for an extended period, yes. Excess unburned fuel overheats the converter. Fix P0108 promptly to protect the cat.
- Does P0108 occur on turbocharged engines specifically?
- Turbocharged engines can see MAP voltages near or above the normally-aspirated maximum during boost, but the sensor and ECM are calibrated for it. P0108 on a turbo engine often means a failed sensor reading above its boost range limit.
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