Code P0108: MAP Sensor Circuit High Input

What Does the P0108 Code Mean?

The P0108 diagnostic trouble code stands for “Manifold Absolute Pressure (MAP) Sensor Circuit High Voltage.” 

It’s triggered when the MAP sensor sends a higher-than-expected signal to the engine control module (ECM). In some vehicles, the MAP sensor also functions as a barometric pressure (BARO) sensor, so this code may apply to both systems if they share the same circuit.

NOTE: A BARO sensor measures atmospheric pressure to help the engine control module adjust fuel delivery and ignition timing based on altitude and weather conditions.

But what does the MAP sensor do?

The MAP sensor measures pressure inside the intake manifold and helps the ECM calculate the right air-fuel mixture. Along with data from sensors like engine speed, air temperature, and the MAF sensor, it ensures efficient combustion by telling the ECM how much air enters the engine. 

The ECM also compares this information with input from the throttle position sensor (TPS) to determine engine load and adjust fuel delivery accordingly. 

The P0108 code occurs when the sensor voltage remains above normal range for too long, typically over 4.5 volts. This high-voltage reading can disrupt how the ECM manages fuel delivery and engine performance.

What Causes the P0108 Code?

Several issues can cause the MAP sensor to send an unusually high voltage signal to the engine control module, triggering code P0108. These include:

• Faulty MAP sensor: The Manifold Absolute Pressure (MAP) sensor may fail due to internal electrical faults, age, or exposure to contaminants like oil or coolant. A bad sensor can send incorrect voltage signals to the ECM, leading to a high voltage reading. 

• Wiring or connector issues: The MAP sensor circuit includes a 5-volt reference wire, a ground wire, and a signal wire. If any of these are shorted, corroded, frayed, or have loose connections, they can create an electrical issue that sends a high-voltage signal to the ECM. Damaged insulation, an open circuit, or poor terminal contact can cause signal spikes, voltage drift, or erratic sensor behavior.

• Vacuum leak or intake pressure issues: Since the MAP sensor measures intake manifold pressure, anything that alters that pressure can result in incorrect pressure readings. A leak caused by a cracked or disconnected vacuum hose, loose intake boot, or leaking intake manifold gasket can throw off intake pressure. This may cause the ECM to interpret normal pressure as abnormally high, triggering the P0108 code. 

4 Common Symptoms of the P0108 Trouble Code

A stored P0108 error code often causes noticeable drivability issues. Here are the most common signs:

1. Check Engine Light Turns On

The first sign is usually the check engine light (CEL). While it can indicate many issues, a scan tool will confirm if the P0108 code triggers it.

2. Rough Idling

You may notice the engine idles roughly, especially when stopped or immediately after starting. A faulty MAP reading can affect ignition timing, making the engine shake or unstable.

3. Poor Performance

A faulty MAP sensor signal can cause sluggish acceleration and poor throttle response. The engine may feel underpowered or hesitate during acceleration.

4. Reduced Fuel Efficiency

The engine may run too rich, burning more fuel than necessary. This often leads to a noticeable drop in miles per gallon (MPG) and more frequent fuel stops.

Can You Still Drive with a P0108 Code?

No, you shouldn’t drive with a P0108 code.

A high MAP sensor signal causes the engine control module to misread the intake pressure and inject too much fuel. This leads to a rich air-fuel mixture, which can cause poor fuel economy, rough idling, hesitation, and increased emissions.

If ignored, it can also result in misfires, spark plug fouling, and damage to the catalytic converter. To avoid more expensive repairs, it’s best to stop driving and have the issue diagnosed by a qualified mechanic as soon as possible.

How to Diagnose the P0108 Code

To diagnose the P0108 error code, a mechanic will typically follow these steps:

1. Scan the vehicle using an OBD-II scan tool to confirm the code and check for related trouble codes.

2. Clear the code and perform a road test to see if it returns.

3. Monitor the MAP sensor voltage reading. It should read ~1 V at idle and up to 5 V at wide-open throttle.

4. Inspect the MAP sensor housing, vacuum lines, and intake ducting for cracks or disconnections.

5. Check the wiring harness and connector for corrosion, loose pins, or damaged insulation.

While some steps can be done at home with the right tools, proper diagnosis is best left to a qualified mechanic to avoid incorrect repairs or unnecessary sensor replacements.

Common Fixes for P0108 and Repair Costs

Several issues can trigger the P0108 code, and the right fix depends on what’s causing the high MAP sensor voltage. Here are some possible solutions and what they typically cost:

• Reset the trouble code: In some cases, especially with high-mileage vehicles, a momentary MAP sensor issue may trigger the code without needing a repair. If the issue doesn’t return, a reset followed by a road test may resolve it.
  • Testing cost: $50 – $170

• Clean or replace the engine air filter: A clogged filter can restrict airflow, leading to false MAP readings.
  • Replacement cost: $55 – $215

• Replace the MAP sensor: If the sensor consistently shows incorrect readings or has faulty wiring connections, it may need replacing.
  • Replacement cost:  $130 – $300

• Inspect vacuum hoses and inlet ducting: Cracked, disconnected, or collapsed vacuum hoses can cause incorrect pressure readings.
  • Repair cost:  $150 – $1,000

• Repair or replace a faulty catalytic converter: If exhaust backpressure builds due to a clogged converter, it may trigger MAP sensor codes.
  • Replacement cost:  $450 – $4,200

Related Trouble Codes to P0108

The P0108 code can appear alongside the following MAP sensor or intake-related trouble codes, helping pinpoint the underlying issue:

• P0068: MAP/MAF/throttle position correlation error
• P0069: MAP/barometric pressure correlation error
• P0105: MAP circuit malfunction
• P0106: MAP sensor range/performance issues
• P0107: MAP sensor low voltage
• P0109: Intermittent MAP sensor signal
• P1106: MAP Sensor Circuit Intermittent High Voltage (manufacturer-specific)
• P1107: MAP Sensor Circuit Intermittent Low Voltage (manufacturer-specific)