Fuel and air

P0108 — Manifold Absolute Pressure (MAP) Sensor Circuit High Input

Severity: medium Drive with care, to a shop

What P0108 means

The engine control module (ECM) reads the MAP sensor to measure intake manifold pressure and calculate engine load and fuel delivery. P0108 sets when the sensor signal voltage stays above the expected range, so the ECM thinks pressure is much higher than it really is. The usual culprits are a failed sensor, a signal wire shorted to power, or an open ground circuit.

Symptoms

  • Check Engine light on
  • Rough or unstable idle
  • Poor fuel economy
  • Hesitation and weak acceleration
  • Black smoke or fuel smell from a rich mixture
  • Stalling
  • Hard starting or no start on some engines

Possible causes

  1. Failed MAP (or BARO) sensor
  2. Signal wire shorted to 5 V or battery voltage
  3. Open sensor ground or poor connector contact
  4. Corroded or damaged connector terminals
  5. Broken or leaking vacuum hose to the sensor (on vacuum-type sensors)
  6. Intake leaks that distort readings
  7. Faulty ECM (rare)

How to diagnose

  1. Scan for all codes and save freeze frame data before clearing anything
  2. Inspect the MAP sensor, connector and harness for chafing, oil, corrosion and loose terminals
  3. Check live data: with key on, engine off, the reading should be near atmospheric pressure, and it should drop noticeably at idle
  4. Test the sensor connector with a multimeter for 5 V reference, ground and signal voltage
  5. Check the sensor ground for an open and the signal wire for a short to power
  6. If the sensor uses a vacuum hose, inspect it and verify the vacuum supply
  7. Look for intake manifold and hose leaks
  8. If wiring tests good and the signal stays high, replace the sensor and retest

Common fixes

  • Replace the MAP (or BARO) sensor
  • Repair or replace the damaged wiring or connector
  • Replace the vacuum hose or fix the intake leak (manifold gasket, hoses)
  • Reflash or replace the ECM only after confirming it is at fault (rare)

Questions and answers

What does P0108 mean?

The ECM is getting an abnormally high voltage from the manifold pressure sensor circuit. It is usually caused by the sensor itself, a wire shorted to power, or an open ground.

Can I drive with P0108?

Only briefly and to a repair shop. The fuel mixture can be wrong, the engine may run rough or stall, and fuel economy will suffer.

How do I tell a bad sensor from a wiring problem?

Measure the 5 V reference, ground and signal at the connector. If reference and ground are good but the signal stays high as vacuum changes, the sensor is bad. Otherwise look for a wiring fault.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.