P0108 Code: Causes of MAP Circuit High Input

Quick answer

The P0108 code means the Engine Control Module (ECM) has detected an abnormally high voltage signal from the Manifold Absolute Pressure (MAP) sensor circuit. This indicates the sensor or its wiring is sending a signal that exceeds the expected range, typically above 4.5 volts, which the ECM interprets as a fault in the MAP sensor's input.

What the P0108 Code Means: MAP Circuit High Input

The Manifold Absolute Pressure (MAP) sensor measures the pressure inside the intake manifold, which the ECM uses to calculate engine load and adjust fuel delivery and ignition timing. A P0108 code is triggered when the ECM sees a voltage signal from the MAP sensor that is higher than its maximum expected value, usually around 4.5-4.9 volts depending on the vehicle. This high voltage suggests either the sensor itself is faulty, the wiring is shorted to a power source, or there is an issue with the sensor's ground or reference voltage.

The MAP sensor operates on a 5-volt reference circuit from the ECM, with the sensor's internal resistor changing based on manifold pressure. At idle or low load, the sensor outputs a low voltage (around 0.5-1.5V), while at wide-open throttle, it may reach 4.5V or slightly higher. When the ECM detects a voltage above this threshold; often due to a short to power in the signal wire, a failed sensor, or a damaged harness; the P0108 code is set. Unlike a P0107 (low input), which often points to a vacuum leak or disconnected wire, P0108 is almost always an electrical issue rather than a performance or mechanical one.

In most fuel-injected engines, the MAP sensor is a three-wire component: a 5V reference wire, a ground wire, and a signal wire that sends voltage back to the ECM. If the signal wire shorts to the 5V reference wire, the ECM sees a constant high voltage, triggering P0108. Similarly, internal failure of the MAP sensor can cause it to output a fixed high voltage. Less commonly, a poor ground or damaged ECM can also cause this code, though these scenarios are rarer and usually accompanied by other diagnostic trouble codes.

Diagnosing a P0108 code starts with checking the MAP sensor's signal voltage with a multimeter or scan tool. If the voltage reads near 5V with the engine off (key on, engine off), this confirms a short to power or a faulty sensor. If the voltage is normal at KOEO but spikes abnormally during operation, the issue may be intermittent, often caused by chafed wiring or a failing sensor. Visually inspecting the MAP sensor's wiring harness for damage, corrosion, or loose connections is a critical step, as physical issues are a common cause of this code.

Common Symptoms of P0108

A P0108 code commonly causes rough idle, poor acceleration, and a noticeable drop in fuel efficiency, as the ECM defaults to a predetermined fuel map when the MAP signal is unreliable. In some cases, the engine may run rich or lean, leading to black or white smoke from the exhaust. These symptoms occur because the ECM cannot accurately gauge engine load, leading to incorrect fuel and timing adjustments.

Typical Causes of P0108

Most P0108 codes are caused by a faulty MAP sensor, a short in the signal wire to the 5V reference circuit, or damaged wiring. Less often, a poor ground or ECM issue may be to blame. Repairs typically range from $150 to $1,000+ depending on the cause; see the full P0108 repair cost guide for a detailed breakdown.

Can You Still Drive With Code P0108?

Driving with a P0108 code is generally possible for short distances, but it is not recommended for extended trips. The vehicle may experience reduced power, poor fuel economy, or stalling, which can be unsafe in traffic. If the engine runs rough or stalls frequently, have the issue diagnosed and repaired promptly to avoid further damage.

Details that improve the diagnosis

Compare the reported value with engine temperature, barometric pressure, throttle position and related sensors. A signal that is electrically valid can still be implausible. Fuel trims at idle and at a steady higher speed help separate an intake leak from a fuel-delivery or measurement problem.

Before clearing anything, record whether the code is current, pending, history or permanent. Save companion codes and freeze-frame conditions, then note recent repairs, a weak battery, weather changes and the exact moment the symptom appears. After a confirmed repair, clear only the erasable codes and complete the appropriate drive cycle. A permanent code normally clears only after the onboard monitor verifies that the fault is gone.

Related trouble codes

Information to record before any repair

Write down the exact code, its status and every companion code reported by a complete vehicle scan. Save the freeze-frame values, including engine speed, load, coolant temperature, vehicle speed, battery voltage and fuel trims when available. Note whether the warning appeared during a cold start, at idle, under acceleration, after refueling, in wet weather or immediately after other work. These details help separate an intermittent electrical problem from a repeatable mechanical or operating-condition fault.

Identify the exact year, make, model, engine, transmission and market version before using a wiring diagram or specification. Connector pinouts, monitor thresholds, component locations and test procedures can change within the same model line. Check current manufacturer service information and relevant technical service bulletins. A bulletin can improve the test sequence, but it should not be treated as proof that the same fault exists on every vehicle.

How to verify the repair

A warning light that stays off immediately after codes are cleared does not by itself confirm a repair. Recheck live data, repeat the operating condition that originally set the code when it is safe to do so, and confirm that no pending code returns. Some monitors need a specific drive cycle before they run. Permanent codes are normally removed by the control module only after it sees enough successful monitor results. If symptoms remain or the code returns, continue testing instead of replacing another part by guesswork.