OBD-II Code P0108 — What It Means & How to Fix It

What Does This Error Mean?

P0108 means the MAP (Manifold Absolute Pressure) sensor is sending a voltage signal that is too high. The MAP sensor measures air pressure in the intake manifold. A voltage that stays too high tells the ECM there is more air pressure than physically possible. This causes the engine to run rich — adding too much fuel. Common causes are a faulty MAP sensor, vacuum leak, or wiring problem.

Affected Models

All vehicles 1996+
Common in Jeep Cherokee
Common in Dodge Durango
Common in GM vehicles with 3.6L
Common in Honda vehicles

Common Causes

Faulty MAP sensor sending a voltage higher than its maximum rated output
Short to voltage in the MAP sensor signal wire causing artificial high readings
Blocked or pinched vacuum hose connecting the MAP sensor to the intake manifold
Failed MAP sensor reference voltage circuit providing too much voltage
Contaminated or damaged MAP sensor diaphragm giving incorrect pressure readings

How to Fix It

Locate the MAP sensor. It is typically a small sensor plugged directly into the intake manifold or connected to it via a short rubber vacuum hose. It will have an electrical connector with usually 3 wires.

On some vehicles the MAP sensor is combined with the IAT (intake air temperature) sensor into one unit. Check your vehicle's service information if you are unsure which sensor is which.
Inspect the vacuum hose connecting the MAP sensor to the intake manifold. Look for kinks, cracks, or blockages. A pinched hose traps high pressure air near the sensor, causing a falsely high reading.

Disconnect the hose at the sensor end and blow through it gently. If it is blocked, clear the obstruction or replace the hose — they cost under $5.
Unplug the MAP sensor connector and inspect for corrosion, bent pins, or moisture inside the connector housing. Clean with electrical contact cleaner if needed. Reconnect and clear the code to test.

Moisture inside a connector can create unexpected voltage readings. If you find water in the connector, seal the repaired connector with dielectric grease.
With a multimeter or scan tool, check the MAP sensor reference voltage. The sensor should receive a 5-volt reference from the ECM. Significantly higher than 5 volts suggests a wiring fault rather than a sensor failure.

If you have a scan tool with live data, watch the MAP reading at key-on engine-off. A normally functioning MAP sensor should read close to local atmospheric pressure (around 14.7 psi at sea level).
Replace the MAP sensor if the vacuum hose and wiring check out fine. This is a simple unplug-and-swap repair on most vehicles. Clear the code and drive to verify the repair.

MAP sensors typically cost $30-$80 for aftermarket and $60-$150 for OEM. On most vehicles, no special tools are needed for replacement.

When to Call a Professional

P0108 is often an inexpensive sensor or wiring fix. A MAP sensor replacement costs $50-$150 in parts plus labor. If the wiring has a short to voltage, a mechanic needs to trace the harness with a wiring diagram. Running rich long-term wastes fuel and can foul spark plugs or damage the catalytic converter. Don't delay beyond a few weeks — the fuel-wasting effects add up quickly.

Frequently Asked Questions

What symptoms does P0108 cause?

The most common symptom is the check engine light. You may also notice rough idle or hesitation during acceleration. The engine may run rich, meaning it uses more fuel than necessary. Black smoke from the exhaust or a strong fuel smell can also occur. In severe cases, the engine may stall or surge at idle.

What is a voltage that is too high for a MAP sensor?

MAP sensors typically output between 0.5 and 4.5 volts. At idle (low manifold pressure), the reading should be around 1-2 volts. Under hard acceleration (higher pressure), it rises toward 4-4.5 volts. P0108 sets when the voltage exceeds the maximum threshold — typically above 4.7 volts. A reading stuck near 5 volts at idle is a clear sign of a sensor or wiring fault.

Is P0108 the opposite of P0107?

Yes, exactly. P0107 is a low input code — the voltage is too low. P0108 is a high input code — the voltage is too high. Both indicate the MAP sensor reading is outside its expected range. The diagnostic steps are similar for both — check the hose, connector, wiring, and then the sensor itself.