What does 'circuit high input' mean on P0108?

It means the voltage on the MAP signal wire is above the range the ECM accepts as valid — the sensor is reporting a manifold pressure at or above atmospheric even at idle, which can't physically happen on a running naturally-aspirated engine. That usually points at a signal wire shorted to voltage, a lost or high-resistance ground, or a sensor that has failed at full scale.

Can a disconnected vacuum hose cause P0108?

On sensors that mount remotely and connect to the manifold through a hose, absolutely — and it's worth checking first because it costs almost nothing. If the hose is cracked, popped off, or the manifold port is plugged with carbon, the sensor simply reads atmospheric pressure and reports it honestly. The ECM sees an impossibly high value and sets the code. Many modern MAP sensors thread directly into the manifold and have no hose, so check which design your engine uses.

Is it safe to drive with P0108?

Short trips are usually possible because most ECMs fall back to a default load value, but the engine will likely run rich, idle poorly, and use more fuel. Prolonged rich running fouls spark plugs, dilutes engine oil with fuel, and can overheat and damage the catalytic converter. Get it diagnosed within days rather than driving on it for weeks.

How is P0108 different from P0107 and P0106?

All three are MAP sensor codes with different fault signatures. P0108 is circuit high — the signal is above the valid range, usually a short to voltage, a bad ground, or a lost vacuum supply. P0107 is circuit low — the signal is below the valid range, usually a short to ground or a disconnected sensor. P0106 is range/performance — the value is technically within range but doesn't match what the engine is actually doing, which often means a vacuum leak or a lazy sensor rather than a hard electrical fault.

OBD-II trouble code

P0108: Manifold Absolute Pressure/Barometric Pressure Circuit High Input

The MAP/BARO sensor signal voltage is above the normal operating range. The ECM is effectively being told the manifold is at or above atmospheric pressure at all times, which throws off fueling and can make the engine run rich, rough, or down on power.

Medium severityPowertrainFuel & Air MeteringDrivable short-term

Quick facts

System: Powertrain
Category: Fuel & Air Metering
Severity: Medium severity
Drivable: Usually safe to drive short-term
Repair cost range: $40 – $350
DIY difficulty: Intermediate DIY

What does P0108 mean?

The manifold absolute pressure (MAP) sensor measures the pressure inside the intake manifold. Because manifold pressure falls as the throttle closes and rises as the throttle opens, that single reading tells the engine control module (ECM) how hard the engine is working — it is the foundation of the speed-density fueling calculation on MAP-based systems and an important cross-check on mass-airflow systems. On most vehicles the same sensor also provides barometric pressure at key-on, before the engine starts, so the ECM can compensate for altitude.

P0108 is the circuit-high member of the MAP family. The sensor's signal wire normally sits somewhere in a range of roughly 0.5 to 4.5 volts, with low voltage representing high vacuum (closed throttle) and high voltage representing low vacuum or boost (wide-open throttle). P0108 sets when the ECM sees the signal pinned above that range and holding — a value that would mean the manifold is at or above atmospheric pressure even at idle, which is physically impossible on a running naturally-aspirated engine.

That is the opposite of P0107 (circuit low) and different again from P0106, which flags an in-range but implausible reading. Because the value is out of range rather than merely suspicious, the causes lean electrical: a signal wire shorted to the 5-volt reference or to battery voltage, an open or high-resistance sensor ground, a corroded connector, or an internally failed sensor stuck at full scale. There is also a genuinely mechanical cause worth checking first on ported designs — a disconnected, cracked, or blocked vacuum hose feeding the sensor. If the sensor never sees manifold vacuum, it honestly reports atmospheric pressure, and the ECM reads that as a high-side fault.

With a MAP reading pinned high, the ECM believes the engine is under heavy load all the time and commands correspondingly more fuel. The result is usually a rich condition: rough idle, black smoke or a fuel smell, poor fuel economy, hesitation, and possibly hard starting. Many vehicles will fall back to a default load value and run acceptably, but leaving it uncorrected can foul plugs, wash cylinder walls with fuel, and over time damage the catalytic converter.

Common causes

Disconnected, cracked, or blocked vacuum hose to the MAP sensor on designs that use one — check this before anything electrical
Signal wire shorted to the 5-volt reference or to battery voltage
Open or high-resistance ground circuit at the sensor
Corroded, water-intruded, or damaged sensor connector
Internally failed MAP sensor stuck at full-scale output
Chafed harness where the MAP wiring passes over the intake or a bracket
Intake manifold port for the sensor plugged with carbon or oil sludge
ECM input circuit fault (rare — verify wiring first)

Symptoms

Check engine light is on
Rough idle or an engine that surges at idle
Rich running — fuel smell, black exhaust smoke, sooty plugs
Noticeably worse fuel economy
Hesitation, stumble, or lack of power under acceleration
Hard starting, especially when the engine is warm
Possible companion fuel-trim or misfire codes from the rich condition

Diagnostic steps

1.Scan and record all codes and freeze-frame data. Note whether reference-voltage codes or other sensor codes are present, which would point at a shared 5-volt circuit rather than the MAP sensor itself.
2.Compare the live MAP reading at key-on-engine-off against the barometric pressure PID. With the engine off they should agree closely — roughly 29 to 30 inHg or about 101 kPa at sea level.
3.Start the engine and watch MAP at idle. A healthy engine pulls the reading well down (typically around 25 to 35 kPa at idle at sea level). A reading that stays near atmospheric confirms the fault.
4.On sensors fed by a vacuum hose, remove and inspect it for cracks, collapse, disconnection, or a carbon-plugged manifold port. This is a common and cheap cause.
5.Inspect the sensor connector for corrosion, moisture, spread terminals, and backed-out pins.
6.With the key on, verify a clean 5-volt reference and a good ground at the sensor connector. A missing or high-resistance ground drives the signal high.
7.Unplug the sensor with the key on and read the signal wire. It should drop toward zero — if it stays high with the sensor disconnected, the signal wire is shorted to voltage.
8.If reference, ground, and signal wiring all check out but the reading stays pinned, replace the MAP sensor and verify the live reading tracks correctly before returning the vehicle.

Repair cost

$40 – $350

A cracked or disconnected vacuum hose can be a genuinely under-$20 fix. The MAP sensor itself is inexpensive — usually $20 to $130 in parts with minimal labor, so a sensor replacement typically lands at $70 to $200. Wiring and connector repairs range from $80 to $300 depending on where the damage is and how much harness has to be opened up. Always confirm the hose, ground, and reference voltage before buying a sensor; a surprising share of P0108 cases are wiring or vacuum problems.

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DIY vs shop

This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.