MAP/Barometric Pressure Circuit High Input
The Powertrain Control Module (PCM) detected a voltage signal from the Manifold Absolute Pressure (MAP) or Barometric Pressure sensor that is higher than the expected normal range. This typically indicates the sensor is reporting an abnormally high pressure (low vacuum) state in the intake manifold when operating conditions dictate otherwise.
While the vehicle will usually still run, it may run poorly, consume excess fuel, and potentially stall. It should be diagnosed soon to prevent drivability issues and catalytic converter damage from a rich fuel mixture.
Common symptoms
- Illuminated Check Engine Light
- Rough idle or engine stalling
- Poor fuel economy
- Engine hesitation or surging during acceleration
- Strong smell of unburned fuel from the exhaust
Likely causes
- Defective MAP or Barometric Pressure sensor
- Vacuum leak in the intake manifold or vacuum hoses
- Damaged, shorted, or corroded wiring in the MAP sensor circuit
- Poor electrical connection at the MAP sensor connector
- Faulty Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Inspect the MAP sensor wiring and connector for visible damage.
Look for: Look for frayed wires, corrosion inside the connector pins, or a loose connection that could cause a short to voltage.
Check for vacuum leaks around the intake manifold and MAP sensor.
Look for: Listen for hissing sounds or use a smoke machine to find leaks that would cause low engine vacuum, which results in a high pressure reading.
Use a scan tool to monitor the MAP sensor live data with the key on, engine off (KOEO).
Look for: The reading should match the local barometric pressure; if it reads significantly higher or shows maximum voltage (e.g., 4.5V to 5V), the sensor or circuit is faulty.
Test the MAP sensor reference voltage and ground circuits with a multimeter.
Look for: Verify there is a steady 5-volt reference from the PCM and a solid ground; a short to voltage on the signal wire indicates a wiring harness issue.
Apply vacuum to the MAP sensor using a hand-held vacuum pump while monitoring the signal voltage.
Look for: The voltage should drop smoothly as vacuum increases; if the voltage remains high and unchanged, the sensor is internally shorted or defective.
This page explains the generic P0108 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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