How much does it cost to fix P0108?

DIY repair typically costs $10–$60 for parts. Professional repair runs $100–$350 including parts and labor.

P0108

Powertrain

Moderate

Manifold Absolute Pressure/Barometric Pressure Circuit High Input

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The P0108 code is set when the engine control module (ECM) detects that the MAP sensor's output voltage exceeds the maximum expected value, typically above about 4.5 volts out of a 5-volt range. A high MAP signal tells the computer that the intake manifold is at or near atmospheric pressure, which normally only happens at wide-open throttle or when the engine is off. If this signal appears at idle or light load, the ECM knows something is wrong.

A failed MAP sensor is the most common cause, but check the vacuum hose first — if it's disconnected or plugged, the sensor will read atmospheric pressure rather than manifold vacuum, producing a high output at idle. Also inspect the wiring harness for chafed insulation where the signal wire might be shorting to a nearby power wire. With the engine off and key on, you can measure the MAP sensor voltage with a multimeter at the connector; it should read around 4.0-4.5V (atmospheric) and drop to around 1.0-2.0V with the engine running at idle.

When the ECM sees a high MAP signal, it thinks the engine is under heavy load and enriches the fuel mixture significantly. This results in a rich running condition with black exhaust smoke, fouled spark plugs, and terrible fuel economy. The catalytic converter can also be damaged by excessive unburned fuel. Plan to fix this within a few days. The MAP sensor is an affordable part and accessible on most vehicles for a straightforward replacement.

Severity

Moderate — Address SoonThis Week

Symptoms

•Check Engine Light is on
•Engine runs very rich with poor fuel economy
•Black smoke from exhaust
•Rough or high idle speed
•Engine backfires or pops
•Reduced power and sluggish throttle response

Likely Causes

Faulty MAP sensor outputting high voltage35%

An internally failed MAP sensor can output a voltage above the maximum expected range, telling the ECM that manifold pressure is much higher than actual, as if the engine is under heavy load.

Short to voltage in MAP sensor wiring25%

If the MAP sensor signal wire contacts a power source due to chafing or connector damage, the ECM reads an artificially high voltage on the MAP input.

Disconnected or blocked vacuum hose20%

A completely disconnected or plugged vacuum hose causes the MAP sensor to read atmospheric (barometric) pressure instead of manifold vacuum, resulting in a higher-than-expected output voltage at idle.

Severe vacuum leak at intake manifold15%

A large vacuum leak such as a cracked intake manifold or blown gasket can reduce manifold vacuum enough that the MAP sensor reads near atmospheric pressure, producing a high signal.

Incorrect MAP sensor installed5%

If the wrong part-number MAP sensor was installed during a previous repair, its calibration may produce voltages outside the ECM's expected range for this specific engine.