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.

Codes › P0108

P0108: The MAP sensor voltage is too high

Manifold Absolute Pressure/Barometric Pressure Circuit High Input

Moderate severityCan you keep driving?

Short distances only. High MAP voltage makes the computer think the engine is under high load all the time, causing over-fueling and rich running. Prolonged rich running damages catalytic converters.

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 it costs

MAP sensor replacement$80 to $250
Wiring repair$100 to $300

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 displays live MAP sensor voltage so you can see whether the reading is pinned at the top or only spikes under certain conditions. Download Lewis.

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.