P0108: Manifold Absolute Pressure - Barometric Pressure Circuit High Input

What P0108 tells you, and what it does not

The computer reads a voltage from the manifold pressure sensor circuit higher than any plausible pressure condition, which usually points to a short to power, a failed sensor, or a wiring fault.

The code sits in the manifold pressure sensor circuit area and is reported by the comprehensive component monitor. It names the circuit or the condition where the computer saw a reading outside its expected range. It does not name a failed part, and several genuinely different faults set this same code, which is the whole reason the causes below are ordered rather than listed.

What people usually notice

• Rich running exhaust smell
• Rough idle
• Poor fuel economy
• Hesitation on acceleration

What causes P0108?

The causes below are ordered by how often they turn out to be the answer, cheapest and most common first. That order matters more than the list itself: the expensive component named in the code text is very rarely the first thing to replace, and working down from the top is what stops a manifold pressure sensor circuit fault becoming an expensive guess.

Sensor signal wire shorted to a power circuit is the one to rule out before anything else. Common after wiring work near the intake manifold.

Working out which cause it is

Start with freeze frame. Manifold pressure at the fault shows how implausibly high the reading was relative to conditions. That snapshot is taken at the instant the code set, and it is the single most useful piece of evidence you have, which is also why clearing the code before reading it is such a costly habit.

This code is diagnosed by watching values change rather than by reading the number again, so the tool has to stream live data and hold freeze frame. Live sensor voltage readings across engine speed and load show whether the signal is pinned near its maximum regardless of actual manifold pressure.

The order worth working in

• 1. Sensor signal wire shorted to a power circuit: Common after wiring work near the intake manifold.
• 2. Failed sensor sending a falsely high signal: Internal sensor damage can push the output past its normal range.
• 3. Damaged or corroded connector causing an internal short: Moisture intrusion can bridge pins that should be separate.
• 4. Loose or pinched wiring harness near the intake manifold: Physical damage from engine movement can create an intermittent short.

What P0108 means for driving the car

The vehicle remains drivable, though the fuel system may run rich until this is corrected.

This is a severity 2 of 4 code. It will not usually strand you, but it will fail an emissions test while it is present, and the underlying fault rarely gets cheaper by being left alone.

What does it cost to ignore P0108?

A falsely rich fuel calculation wastes fuel and fouls spark plugs faster, and over time can load the catalytic converter with unburned fuel.

There is also the diagnostic cost of waiting. Freeze frame data, pending code history and the readiness monitor state all describe the fault as it was when it set, and all of it is lost the moment somebody clears the code to make the lamp go out.