P0108: MAP Sensor Circuit High Input

Quick answer

• What the code means: The P0108 code means the Manifold Absolute Pressure (MAP) sensor is reporting an abnormally high voltage signal to the powertrain control module (PCM).
• Severity: Safe to keep driving, but address the issue as soon as possible to avoid poor fuel economy and potential engine damage.
• Most common cause: A faulty MAP sensor.

What the P0108 code means

The official OBD-II definition for P0108 is "Manifold Absolute Pressure/Barometric Pressure Circuit High Input." In plain English, this means the engine's computer (the PCM) is seeing a voltage from the MAP sensor that is higher than the normal operating range. The MAP sensor measures the pressure inside the intake manifold, which is a key indicator of engine load. This information, along with data from other sensors, is used by the PCM to calculate the correct amount of fuel and ignition timing.

When the PCM detects a voltage from the MAP sensor that is above the expected range (typically above 4.5 volts) for a set period of time, it will trigger the P0108 trouble code and illuminate the Check Engine Light.

Common symptoms

When the MAP sensor sends a false high-pressure signal, the PCM may incorrectly deliver too much fuel. This can lead to a variety of noticeable symptoms:

• Check Engine Light (CEL) is on
• Rough idle
• Poor fuel economy
• Engine hesitation or stumbling on acceleration
• Black smoke from the exhaust
• Failed emissions test
• In some cases, the engine may be hard to start or may not start at all.

Common causes

The causes of a P0108 code are usually related to the MAP sensor itself or its electrical circuit. Here are the most common causes, ranked from most to least likely:

1. Faulty MAP sensor: This is the most common cause. Over time, the sensor can fail and send an incorrect voltage signal.
2. Wiring or connector issues: A damaged, corroded, or loose connector at the MAP sensor can cause a high-resistance condition, leading to a high voltage reading. The wiring harness itself can also be damaged, causing a short or open circuit.
3. Vacuum leaks: While less common for a "high input" code, a significant vacuum leak can sometimes cause an erratic signal from the MAP sensor that the PCM interprets as a fault.
4. Clogged catalytic converter: A restricted exhaust can cause an increase in manifold pressure, which the MAP sensor will report. This is a less common cause but should be considered if other diagnostic steps don't reveal the problem.
5. Faulty PCM: In rare cases, the PCM itself may be faulty and misinterpreting the MAP sensor signal. This should be the last thing to consider after all other possibilities have been ruled out.

How a technician diagnoses it

A technician will use a systematic approach to diagnose a P0108 code. Here are the typical steps:

1. Scan for codes: The technician will connect an OBD-II scanner to the vehicle's diagnostic port to confirm the P0108 code and check for any other related codes.
2. Inspect freeze-frame data: This data provides a snapshot of the engine's operating conditions at the moment the code was set. The technician will look at the MAP sensor reading, engine RPM, vehicle speed, and other parameters to get a better understanding of the problem.
3. Visual inspection: The technician will visually inspect the MAP sensor, its connector, and the wiring harness for any obvious signs of damage, corrosion, or looseness. They will also inspect the vacuum hoses connected to the intake manifold for cracks or leaks.
4. Test the MAP sensor: With the engine off, the technician will use a multimeter to check the voltage at the MAP sensor's signal wire. It should typically read around 4.5-5.0 volts. With the engine running at idle, the voltage should drop to around 1.0-1.5 volts. If the voltage remains high with the engine running, it's a strong indication that the sensor is faulty.
5. Check for vacuum: The technician will use a vacuum gauge to check for proper vacuum at the MAP sensor. A low vacuum reading could indicate a vacuum leak or a restriction in the exhaust.
6. Test the wiring: If the MAP sensor itself seems to be functioning correctly, the technician will test the wiring between the sensor and the PCM for continuity and resistance. This will help identify any shorts, opens, or high-resistance conditions in the circuit.
7. Test the PCM: If all other tests come back normal, the technician may suspect a faulty PCM. However, this is a last resort, as PCM failure is rare.

Typical repair cost

The cost to repair a P0108 code can vary depending on the cause of the problem and the make and model of the vehicle. Here are some typical cost ranges:

• MAP sensor replacement: The part itself usually costs between $50 and $150. Labor to replace it is typically around $50 to $100, for a total cost of $100 to $250.
• Wiring repair: If the issue is a damaged wire or connector, the repair cost can be anywhere from $50 to $300, depending on the extent of the damage and the labor involved.
• Vacuum leak repair: The cost to repair a vacuum leak can vary widely, from as little as $20 for a new vacuum hose to $300 or more for a more complex repair, such as replacing an intake manifold gasket.
• Catalytic converter replacement: This is a more expensive repair, with parts and labor typically costing between $500 and $2,500.
• PCM replacement: A new PCM can cost anywhere from $500 to $1,500, plus labor for installation and programming.

Can I keep driving with this code?

Yes, it is generally safe to drive with a P0108 code, but it is not recommended for an extended period. The engine will not be running efficiently, which will lead to poor fuel economy and could potentially cause damage to the catalytic converter over time. It's best to have the vehicle diagnosed and repaired as soon as possible.

Related codes

• P0105: Manifold Absolute Pressure/Barometric Pressure Circuit Malfunction
• P0106: Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance Problem
• P0107: Manifold Absolute Pressure/Barometric Pressure Circuit Low Input
• P0109: Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent

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