The P0108 fault code indicates a MAP sensor circuit high input, meaning the engine control unit is receiving a MAP sensor voltage that’s higher than expected. In practice, this usually points to a faulty MAP sensor, wiring or connector problems, or a PCM issue. Replacing the sensor or repairing the associated wiring often resolves the problem.
The MAP sensor measures manifold pressure and feeds that data to the ECU to calculate load and fuel delivery. A voltage reading near the sensor’s maximum (close to 5V) can trigger P0108, especially in engines with boost or turbocharging. This article outlines how to diagnose and fix P0108 with steps suitable for both DIYers and professionals.
Understanding P0108
P0108 stands for “MAP Sensor Circuit High Input.” MAP sensors typically output a voltage that ranges roughly from 0.5V (low/manual idle) up to about 4.5V (higher engine load). When the ECU sees a voltage at or near the supply voltage (often 5V) on the MAP signal line, it may set P0108 to indicate an abnormally high reading. In turbocharged or supercharged systems, the sensor can be pushed toward its upper limit by boost, or a fault can cause the reading to stay high regardless of actual manifold pressure. This can lead to drivability issues and a Check Engine Light are common symptoms.
Symptoms you might notice
If P0108 is active, you may observe the following indicators:
- Check Engine Light (CEL) illuminated
- Rough or unstable idle
- Reduced power or hesitation during acceleration
- Surging or stalling at low speeds
- Unusual fuel trims or misfire codes
Diagnosing P0108 requires verifying whether the high reading is sensor- or wiring-related versus a PCM fault, and then confirming with measurements and tests.
Common causes
The following items are the most frequent sources of a P0108 code. Inspecting and testing these components is a practical first step.
- Faulty MAP sensor itself (stuck high or defective)
- Damaged, corroded, or loose MAP sensor wiring or connector
- Short to power or a ground fault on the MAP signal circuit
- Vacuum/pressure reference line to the MAP sensor is cracked, disconnected, or leaking
- PCM/ECU fault or software issue
- Aftermarket parts or improper installation affecting MAP readings
Most fixes involve sensor replacement or wiring repair; in rare cases, software updates or PCM replacement may be required.
Troubleshooting steps
To identify and fix P0108, follow a structured diagnostic approach. The steps below outline a practical path from data collection to verification.
- Retrieve freeze-frame data and note the exact MAP readings, engine RPM, load, and temperature at the time of the fault.
- Visually inspect the MAP sensor and its harness: look for damaged wires, corrosion, bent pins, cracks in the sensor body, and a loose connector. Inspect the vacuum/pressure hose connected to the MAP sensor for cracks or disconnections.
- Verify the 5V reference and ground circuits using a multimeter. Check that the MAP signal wire has a solid connection to the MAP sensor and to the ECU without shorts to power or ground.
- With the engine idling and at various RPMs, backprobe the MAP sensor output voltage. In a typical non-turbo engine, you should see a voltage that rises with load (for many cars around ~1-2V at idle and up to ~4.5V at high load). If the signal sits near 5V regardless of conditions, suspect the sensor or wiring.
- Check for short to 5V or short to ground on the MAP signal line. Disconnect the MAP sensor and test continuity between the signal pin and each circuit; look for unexpected paths to power or ground.
- If the harness and sensor appear sound, swap in a known-good MAP sensor to confirm whether the fault follows the sensor. If the code clears with a new sensor, the original sensor was faulty.
- Inspect for vacuum leaks or boost-related issues (especially on turbocharged engines). A leak or incorrect piping can cause erroneous readings, so perform a leak test around the intake and MAP reference hose.
- When wiring and sensor tests are complete, clear the codes and perform a road test to confirm that P0108 does not return under normal driving conditions.
These steps help differentiate sensor problems from wiring or ECM issues, and guide you toward a reliable fix.
When to replace parts
Replace parts only after confirming the faulty component. Replace the MAP sensor if tests show an abnormal output or if swapping with a known-good sensor resolves the issue. If wiring tests reveal a damaged harness or connector, repair or replace the affected wiring and connector. If all hardware checks pass and the code persists, a PCM/ECU fault or software issue may be responsible and may require dealer-level diagnosis or software updates.
Preventive maintenance
To reduce the likelihood of P0108 recurring, implement these maintenance practices:
- Keep MAP sensor and its area clean; avoid moisture and debris contamination
- Inspect and replace cracked or brittle vacuum/pressure lines promptly
- Ensure connectors are dry, clean, and tightly seated; replace damaged connectors
- Avoid aftermarket parts that interfere with MAP readings unless they are designed for your vehicle
- Keep engine software up to date as recommended by the manufacturer
Regular inspection of the intake system and related sensors helps catch issues before they trigger trouble codes.
Summary
The P0108 code signals a MAP sensor circuit high input, most often caused by a bad MAP sensor, damaged wiring or connector, or a short to power on the signal line. A systematic diagnostic approach—checking sensor condition, electrical references, vacuum lines, and ECU health—usually resolves the issue. In many cases, replacing the MAP sensor or repairing wiring fixes the fault; if the problem persists after these steps, seek professional diagnostic support to explore PCM-related causes or software updates.
How do I reset my MAP sensor?
Reset the MAF sensor by idling your engine without the sensor installed for at least 10 seconds. You can also reset the MAF sensor by removing the negative battery terminal and waiting 10 minutes. You may be able to drive without the MAF sensor, but it's bad for your engine to drive without the sensor for too long.
Can I drive with a bad MAP sensor?
Can You Drive with a Bad MAP Sensor. Technically, yes — but it's not a good idea. Driving with a malfunctioning MAP sensor compromises your fuel economy and may eventually damage the engine or catalytic converter.
Can a vacuum leak cause a P0108 code?
Loose connectors, moisture buildup in the wire harness and frayed wires are all common issues that could cause error code P0108. Finally, if your sensor is working properly, there may be a vacuum leak in your engine. Check the vacuum hoses and connectors to ensure a proper seal.
How do I fix trouble code P0108?
How is the P0108 error code repaired?
- Secure connections on the MAP sensor's circuit.
- Replace the MAP sensor's damaged wiring or connectors.
- Replace the faulty MAP sensor.
- Inspect and fix any vacuum leaks in the intake manifold or hoses.
- Reset the error code and perform a test drive to ensure the issue is resolved.