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

The Diagnostic Trouble Code (DTC) P0108 indicates that the Engine Control Module (ECM/PCM) has detected a higher-than-expected voltage signal from the Manifold Absolute Pressure (MAP) sensor. This means the MAP sensor is reporting unusually high intake manifold pressure, which may be caused by an electrical fault, sensor failure, or engine-related problem.

Symptoms

• Check Engine Light is illuminated.
• Rough idle.
• Poor acceleration.
• Reduced engine performance.
• Rich fuel mixture.
• Increased fuel consumption.
• Possible black exhaust smoke.

Possible Causes

• Faulty MAP sensor.
• Short to voltage in the signal circuit.
• Open ground circuit.
• Damaged electrical connector.
• Open or damaged vacuum hose (if equipped).
• Wiring harness damage.
• Incorrect sensor installation.
• ECM fault (rare).

Diagnostic Procedure

1. Read all stored and pending DTCs.
2. Inspect the MAP sensor connector and wiring.
3. Verify the 5V reference, signal, and ground circuits.
4. Inspect the MAP vacuum hose for damage (if equipped).
5. Check for short-to-voltage conditions.
6. Compare MAP live data with throttle position and RPM.
7. Replace the MAP sensor only after confirming failure.

Live Data Diagnosis (Autel Scanner)

Using an Autel scan tool:

1. Navigate to ECM → Live Data.
2. Monitor the MAP (kPa) parameter.
3. With the ignition ON and engine OFF, the MAP value should typically read 95–101 kPa, depending on altitude.
4. At idle, the reading usually drops to approximately 25–40 kPa on naturally aspirated gasoline engines.
5. If the MAP value remains excessively high at idle or does not change correctly with throttle movement, inspect the sensor, wiring, and vacuum supply.

Typical MAP Signal Path

Intake Manifold
       │
       ▼
   MAP Sensor
       │
     Signal
       ▼
    ECM / PCM
       │
Fuel & Ignition Control

Note: Sensor voltage, connector pin assignments, wiring colors, and vacuum hose configuration vary by manufacturer and engine design. Always refer to the correct service manual for the specific vehicle.

Smoke Test

If a smoke machine is available, inspect the intake system for leaks.

• Check intake hoses.
• Inspect vacuum hoses.
• Inspect the intake manifold gasket.
• Repair any leaks found during testing.

Although P0108 is primarily a high-input electrical fault, confirming the intake system is leak-free is an important part of diagnosis.

Common Repairs

• Repair damaged wiring.
• Repair a short-to-voltage condition.
• Restore the ground circuit.
• Replace damaged vacuum hoses.
• Replace the MAP sensor if testing confirms failure.

Important Note

P0108 does not always indicate a failed MAP sensor. Check the electrical circuits, live data, and vacuum system carefully before replacing the sensor.