P0108 Code: Manifold Absolute Pressure/Barometric Pressure Circuit High Input

When your vehicle’s diagnostic system detects code P0108, it’s telling you that the MAP (Manifold Absolute Pressure) sensor circuit is reporting a signal voltage that exceeds the expected range. The MAP sensor is critical for engine performance—it measures the pressure inside the intake manifold and helps the engine computer determine the correct air-fuel mixture. When this sensor malfunctions, your engine may run poorly, consume more fuel, or trigger the check engine light.

What Does P0108 Mean?

The P0108 code specifically refers to a “Manifold Absolute Pressure/Barometric Pressure Circuit High Input” condition. Here’s the technical breakdown:

• P = Powertrain code
• 0 = Generic OBD-II code (applies to all manufacturers)
• 1 = Fuel and air metering system
• 08 = Manifold Absolute Pressure sensor circuit high voltage

Your engine control module (ECM) continuously monitors the voltage output from the MAP sensor. The sensor normally produces a voltage between 0.5V and 4.5V, with higher voltages indicating lower manifold pressure and lower voltages indicating higher manifold pressure. When the ECM detects a signal above the maximum expected threshold, it sets code P0108.

The MAP sensor works by measuring the absolute pressure in the intake manifold and comparing it to atmospheric pressure. This data helps the engine computer calculate the engine load and adjust fuel injection timing and duration accordingly. A faulty high reading tells the engine that there’s less air in the manifold than there actually is, causing it to inject too much fuel.

Common Symptoms

Drivers typically notice one or more of these symptoms when P0108 is active:

• Check Engine Light – The most obvious indicator; the light will remain on while the code is stored
• Poor Fuel Economy – The engine runs rich (too much fuel), causing noticeably worse MPG
• Rough Idle – The engine may shake or feel unstable at traffic lights or stop signs
• Engine Hesitation – Delayed throttle response or stumbling when accelerating
• Black Smoke from Exhaust – Excess fuel creates visible dark exhaust smoke
• Difficulty Starting – Cold starts may be harder or take longer than normal
• Reduced Power – The vehicle may feel sluggish or lack its normal acceleration
• Knocking or Pinging – Engine detonation caused by overly rich fuel mixture

Possible Causes (Ranked by Frequency)

1. Faulty MAP Sensor (Most Common) – The sensor itself has failed and is sending an incorrect high voltage signal. This is the root cause in approximately 60-70% of P0108 cases. MAP sensors can fail due to age, contamination, or internal circuit damage.
2. Vacuum Leak – A leak in the vacuum line connected to the MAP sensor causes it to read lower manifold pressure than actual, resulting in a high voltage output. Check all vacuum hoses for cracks, splits, or loose connections.
3. Wiring Issues – Corroded, damaged, or loose wiring in the MAP sensor circuit can cause signal transmission problems. Inspect the connector and wires for corrosion, breaks, or poor connections.
4. Faulty Engine Control Module (ECM) – Rarely, the ECM itself may have a defect causing it to misinterpret the MAP sensor signal. This is typically a last-resort diagnosis.
5. Contaminated MAP Sensor – Oil, carbon, or fuel deposits on the sensor’s diaphragm can affect its accuracy and cause high readings.
6. Intake Manifold Gasket Leak – A leaking gasket can cause vacuum issues that indirectly affect MAP sensor readings.
7. Barometric Pressure Sensor Failure – Some vehicles use a separate barometric pressure sensor; if it fails, the MAP reading becomes inaccurate.

Diagnostic Steps

Follow these steps to diagnose and fix code P0108:

Step 1: Scan the Vehicle

Use an OBD-II scanner to confirm code P0108 is present and check for any additional codes. Note the freeze frame data, which shows engine conditions when the code was triggered. Clear the code and take a test drive to see if it returns immediately (indicating an active problem) or takes time to reappear (suggesting an intermittent issue).

Step 2: Visually Inspect the MAP Sensor and Vacuum Lines

Locate the MAP sensor (typically mounted on or near the intake manifold; consult your vehicle’s service manual for exact location). Inspect the vacuum hose connected to it for cracks, splits, or loose connections. Check the sensor connector for corrosion or damage. Look for any obvious signs of oil or carbon buildup on the sensor.

Step 3: Check Vacuum Hoses

Trace all vacuum lines from the intake manifold. Look for:

• Cracks or splits in the rubber hose
• Loose or disconnected fittings
• Hoses that have slipped off their connections
• Deteriorated or hardened hose material

A common trick: spray a light mist of water around vacuum connections while the engine idles. If RPMs change, you’ve found a leak.

Step 4: Test MAP Sensor Voltage

Using a digital multimeter set to voltage mode, backprobe the MAP sensor’s signal wire (consult your service manual for the correct pin). With the engine off, the voltage should read around 0.5V. Start the engine and observe the voltage at idle—it should be approximately 1.5-2V. Accelerate and watch the voltage decrease as manifold pressure increases. If the voltage is consistently above 4.5V or doesn’t change with throttle input, the sensor is faulty.

Step 5: Inspect the MAP Sensor Connector

Disconnect the MAP sensor connector and inspect for:

• Corrosion or white/green oxidation on the pins
• Bent or damaged pins
• Moisture inside the connector

Clean corroded connectors with electrical contact cleaner and a small brush. If pins are damaged, the connector may need replacement.

Step 6: Replace the MAP Sensor

If voltage testing confirms the sensor is faulty, replacement is the most common fix. Disconnect the vacuum hose and electrical connector, unbolt the sensor (usually 1-2 bolts), and install the new sensor. Ensure the vacuum hose is firmly connected. Clear the code with your scanner and test drive to confirm resolution.

Step 7: Repair Vacuum Leaks (if found)

If you’ve identified a vacuum leak, repair or replace the affected hose. For loose connections, simply reconnect and secure with a hose clamp if necessary. For cracked hoses, replacement is required.

Step 8: Clear the Code and Verify

After repairs, use your OBD-II scanner to clear code P0108. Take the vehicle on a 10-15 minute test drive covering various speeds and loads. If the code doesn’t return, the repair was successful.

Repair Cost Estimates

The cost to repair P0108 varies depending on the root cause and your vehicle:

• MAP Sensor Replacement: $150–$400
  • Parts: $50–$150
  • Labor: $100–$250 (typically 0.5–1 hour)
• Vacuum Hose Repair/Replacement: $50–$200
  • Parts: $10–$50
  • Labor: $40–$150
• Wiring Repair/Connector Replacement: $75–$300
  • Parts: $20–$100
  • Labor: $55–$200
• Intake Manifold Gasket Replacement: $300–$800
  • Parts: $100–$300
  • Labor: $200–$500 (more involved repair)
• ECM Replacement (rare): $800–$2,000+
  • Parts: $500–$1,500
  • Labor: $300–$500

Note: Prices vary by location, vehicle make/model, and repair facility. Dealerships typically charge more than independent shops. Always get a diagnostic fee waived if you authorize repairs at that facility.

Can I Still Drive?

Severity: Moderate

Code P0108 is not an emergency, and you can typically drive the vehicle safely in the short term. However, continued driving is not recommended for extended periods:

• Short trips (under 10 miles): Generally safe. The vehicle will run, though with reduced fuel economy and possible rough idle.
• Highway driving: Proceed with caution. Poor fuel economy and hesitation could affect performance, but the engine won’t suddenly fail.
• Extended driving: Not recommended. The overly rich fuel mixture can damage the catalytic converter over time, leading to much more expensive repairs ($800–$2,000+).
• Performance impact: You’ll notice noticeably worse fuel economy (often 20-30% reduction), sluggish acceleration, and rough running. The vehicle is drivable but unpleasant.

Best practice: Have the code diagnosed and repaired within a few days to avoid potential damage to the catalytic converter and to restore normal fuel economy.

Frequently Asked Questions