P0108
Manifold Absolute Pressure/Barometric Pressure Circuit High InputP0108 is a generic OBD-II powertrain diagnostic trouble code: Manifold Absolute Pressure/Barometric Pressure Circuit High Input. It is logged by the engine control unit when the air/maf monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0108 means
P0108 is stored when the ECM/PCM detects a MAP sensor signal voltage at or above approximately 4.8 V — beyond the expected maximum of around 4.5 V at wide-open throttle. A voltage this high suggests the signal wire has shorted to the 5 V sensor reference supply, the sensor itself has failed with its output rail-high, or the sensor ground has been lost, which causes the signal to float upward toward the reference voltage.
When the ECM sees a falsely high MAP signal it interprets this as very high intake manifold pressure (low vacuum), similar to a wide-open-throttle condition. The response is to command a richer-than-necessary fuel mixture at all engine loads. In practice this produces poor fuel economy, black exhaust smoke, rough idle, hesitation on acceleration, and over time can foul spark plugs and damage the catalytic converter. Some vehicles enter a limp mode while the code is active.
Because P0107 and P0108 are mirror faults on the same circuit, diagnosis follows the same systematic path: check the vacuum reference first, then inspect wiring and the connector for a short to the reference line, then test sensor operation in isolation. Replacing the MAP sensor resolves the majority of P0108 cases when no wiring fault is found.
Common causes
Most-frequently reported root causes when P0108 is logged.
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1
Defective MAP sensor with an internal electrical fault causing the output to rail at or above 4.8 V.
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2
Signal wire shorted to the 5 V sensor reference wire, forcing the signal line high.
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3
Open or broken sensor ground wire, allowing the signal to float toward the reference voltage.
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4
Corroded or damaged connector pins creating a high-resistance ground path.
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5
Water or oil contamination inside the sensor body creating an internal short to the reference supply.
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6
Cracked or blocked vacuum port on the sensor causing incorrect pressure measurement on certain MAP types.
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7
Faulty PCM/ECM (rare — eliminate all external causes first).
Symptoms drivers notice
How to diagnose P0108
A typical diagnostic flow when this code is present.
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1
Connect an OBD-II scanner, record freeze-frame data, and check for companion codes such as P0107 or fuel-trim codes (P0172, P0175).
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2
Inspect the MAP sensor vacuum hose and intake for blockages or collapsed passages that could falsely elevate pressure readings.
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3
Visually inspect the wiring harness and connector for chafing, melted insulation, or wires pinched against each other — look specifically for signal-wire contact with the 5 V reference wire.
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4
With the connector unplugged, measure resistance between the signal pin and reference pin in the harness; any reading below 1 MΩ indicates a short that must be repaired.
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5
With ignition on (engine off), back-probe the sensor connector and verify 5 V on the reference pin and solid ground (less than 0.1 V) on the ground pin.
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6
Reconnect the sensor and monitor MAP voltage live on the scanner; it should drop at idle as vacuum builds — a reading that stays above 4.5 V confirms a sensor or circuit fault.
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7
Substitute a known-good MAP sensor; if voltage returns to normal, replace the original sensor.
Related powertrain codes
- P0068 — MAP/MAF - Throttle Position Correlation
- P006A — MAP - Mass or Volume Air Flow Correlation Bank 1
- P00B8 — MAP - Mass or Volume Air Flow Correlation Bank 2
- P00BC — Mass or Volume Air Flow A Circuit Range/Performance - Air Flow Too Low
- P00BD — Mass or Volume Air Flow A Circuit Range/Performance - Air Flow Too High
- P00BE — Mass or Volume Air Flow B Circuit Range/Performance - Air Flow Too Low
Frequently asked questions
Will P0108 cause the engine to run rich or lean?
Rich. A high MAP signal tells the ECM that manifold pressure is very high (low vacuum), mimicking a full-throttle condition. The ECM responds by adding more fuel than is actually needed.
What is the maximum normal MAP sensor voltage?
Approximately 4.5 V at wide-open throttle. A sustained reading above this threshold — typically above 4.8 V — triggers P0108 on most vehicles.
Can a clogged vacuum port cause P0108?
On some analog-style MAP sensors, yes — a blocked port traps a pressure reading instead of tracking live manifold vacuum, and the resulting voltage may climb outside the expected range.
Is P0108 dangerous to ignore?
Long-term operation with a rich mixture fouls spark plugs, degrades the catalytic converter, and can wash cylinder walls with unburnt fuel. Address it within a few drive cycles.
Disabling P0108 in software
RaceTune can permanently disable P0108 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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