P0108 Generic (SAE)

Manifold Absolute Pressure / Barometric Pressure Circuit High Input

Updated 2026-10-02 · Fuel & air metering

Severity

Medium

Typical repair cost

20 – 300 EUR

System

Powertrain

What it means

P0108 sets when the MAP signal voltage exceeds the upper plausible limit, typically above 4.8-4.9 V, or stays at atmospheric pressure while the engine is clearly running under vacuum at idle. Electrically this means the signal is shorted to the reference or battery, the ground is lost, or the sensor has failed high. On turbocharged engines the threshold is higher (sensor scaled to 250-300 kPa), but the logic is the same.

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Symptoms

Check engine light with the ECU assuming full load at all times
Very rich running: black smoke, fuel smell, fouled spark plugs
Rough idle, stalling when warm, hard hot restart
Noticeably high fuel consumption
Turbo engines may cut boost or go into limp mode

Common causes

Vacuum hose to the sensor cracked, blocked or disconnected (sensor sees atmosphere)
Open ground wire or corroded ground pin at the sensor
Signal wire shorted to the 5 V reference or to 12 V
Sensor failed internally with output stuck at maximum
Severe intake leak or stuck-open throttle leaving little vacuum (ECU rejects reading)
Port in the manifold blocked with carbon on direct-mount sensors

How to diagnose

Compare MAP to barometric pressure in live data at warm idle: MAP should be 30-45 kPa while BARO stays about 100 kPa; equal values mean the sensor is not seeing vacuum
Check the vacuum supply with a gauge at the sensor port: expect 55-70 kPa vacuum (16-21 inHg) at idle; little or none means a hose or port problem, not a sensor fault
Measure the ground pin: more than 0.2 V above battery negative indicates a bad ground, which pushes the signal high
Key on, engine off, read signal: 4.0-4.7 V is normal; a steady 5.0 V or 12 V means a short to reference or battery; unplug the sensor and if the wire still reads 5 V/12 V the harness is at fault
Apply vacuum with a hand pump directly to the sensor: voltage must drop by about 0.8 V per 20 kPa; no change means a failed sensor
On direct-mount sensors remove and inspect the port for carbon; clean with throttle cleaner and a soft pick

Frequently asked questions

Why does P0108 make the car run rich?

The ECU reads high manifold pressure as heavy load and injects fuel accordingly, even at idle where actual airflow is small.

I replaced the MAP sensor and P0108 came back. Why?

Check the vacuum hose, the port in the manifold and the ground wire. A new sensor cannot read vacuum that never reaches it.