P0108 – Manifold Absolute Pressure/Barometric Pressure Circuit High Input

P0108 is a common OBD-II trouble code that points to a problem with your engine’s MAP (Manifold Absolute Pressure) sensor circuit. When this code sets, your ECU is seeing a MAP signal that’s higher than it should be, which throws off fuel and ignition calculations. That can lead to rough running, poor fuel economy, and potential long-term engine damage if you ignore it. In this guide, you’ll learn what P0108 means, typical symptoms, likely causes, how to diagnose it at home, and what repairs usually cost.

What Does P0108 Mean?

P0108 stands for “MAP Sensor Circuit High Input.” The MAP sensor measures the pressure (or vacuum) in your intake manifold and sends a voltage signal to the ECU. The ECU uses this information to calculate engine load and determine how much fuel and ignition timing the engine needs.

When the ECU sees a MAP signal voltage that’s too high for the current operating conditions (usually above about 4.5–5.0 volts) for a certain time, it flags P0108. This usually means the sensor is lying, the wiring is compromised, or there’s a reference/ground issue causing the signal to spike.

Quick Reference

• Code: P0108 – MAP Sensor Circuit High Input
• System: Engine air/fuel management
• Severity: Moderate to high – can cause drivability issues
• Common Culprits: Faulty MAP sensor, wiring issues, vacuum problems
• Typical Fix: Repair wiring or replace MAP sensor and clear codes

Real-World Example / Field Notes

In the shop, I see P0108 a lot on daily drivers that haven’t had much maintenance. A typical case: a compact sedan comes in with a check engine light, rough idle, and heavy fuel smell. Scan tool shows P0108 and long-term fuel trims pegged rich. A quick visual check reveals the MAP sensor connector half broken and green with corrosion. After cleaning the terminals and replacing the connector pigtail, the MAP voltage returned to normal, fuel trims settled, and the car ran smoothly again—no new sensor needed.

Symptoms of P0108

• Check engine light on: P0108 usually sets the MIL and may store as a pending code first.
• Rough idle: Engine may idle high, surge, or feel like it’s about to stall.
• Poor fuel economy: ECU often enriches the mixture, burning more fuel than normal.
• Black exhaust smoke: Excess fuel can cause dark, sooty exhaust, especially on acceleration.
• Hesitation or lack of power: Incorrect load calculation can cause bogging or sluggish response.
• Hard starting: Over-fueling can make hot or cold starts more difficult.
• Strong fuel smell: You might notice a raw fuel odor from the tailpipe or under the hood.

Common Causes of P0108

Most Common Causes

• Faulty MAP sensor: Internal failure or contamination can cause the sensor to output a constant high voltage.
• Short to voltage in signal wire: Damaged insulation or rubbing harness can let 5V reference bleed into the signal circuit.
• Bad MAP connector or corrosion: Loose pins, spread terminals, or corrosion can skew the signal high.
• Vacuum hose issues (remote-mounted MAP): Cracked, disconnected, or restricted MAP vacuum hose can trick the sensor reading.
• Incorrect sensor type installed: Aftermarket or wrong-part MAP sensor can output the wrong voltage range.

Less Common Causes

• 5V reference circuit fault: A problem with the shared 5V reference (often used by multiple sensors) can raise the MAP reading.
• Poor ground to MAP sensor: High resistance on the ground wire can cause falsely high signal voltage.
• ECU (PCM) internal fault: Rare, but a damaged ECU input circuit can misread the MAP signal.
• Aftermarket tuning issues: Aggressive or incorrect ECU tunes can alter how MAP data is interpreted and trigger P0108.
• Severe engine mechanical problems: Extreme intake modifications or engine damage can confuse sensor readings, though this is uncommon.

Diagnosis: Step-by-Step Guide

Basic tools help a lot here: a quality OBD-II scan tool (preferably with live data and Mode $06), a digital multimeter, and sometimes a handheld vacuum pump. Access to a wiring diagram and MAP sensor specs for your vehicle is also very helpful.

1. Confirm the code and check for companions. Scan for P0108 and any related codes (like P0106, P0107, or misfire codes). Multiple codes can point you toward wiring or shared 5V reference issues.
2. Look at live MAP data. With the key on, engine off (KOEO), MAP should read close to your local barometric pressure (around 100 kPa or 14.5 psi at sea level). If it’s maxed out or clearly wrong, suspect the sensor or wiring.
3. Inspect the MAP sensor and connector. Check for broken housings, oil or coolant contamination, loose pins, corrosion, or a cracked vacuum hose if your MAP is remote-mounted.
4. Check the 5V reference and ground. With a multimeter, back-probe the connector. You should see about 5 volts on the reference wire and near 0 volts on the ground wire relative to battery negative. Any big deviation needs to be fixed first.
5. Measure the signal voltage. KOEO, the signal is typically around 4–4.8V (atmospheric pressure). At idle (high vacuum), many systems drop closer to 1–2V. If the signal stays pinned high regardless of engine condition, you likely have a short to voltage or a bad sensor.
6. Wiggle test the harness. While watching live data or your meter, gently move the wiring harness near the MAP. If the reading spikes or drops, you’ve found an intermittent wiring issue.
7. Use a vacuum pump (if applicable). For a remote MAP sensor, apply vacuum with the engine off while watching the signal. Voltage should smoothly decrease as vacuum increases. No change usually means a failed sensor.
8. Check Mode $06 (if available). Some scan tools show MAP-related test results under Mode $06. This can confirm whether the ECU has seen borderline readings even before a hard code sets.
9. Eliminate other 5V reference problems. If other sensors sharing the 5V line (like TPS or crank sensor) also show odd readings or codes, you may have a shorted sensor elsewhere pulling the circuit high.
10. Consider ECU testing last. Only after wiring and sensor checks pass should you suspect a PCM fault. This often requires professional-level tools or an experienced shop.

Pro tip: Never replace the MAP sensor just because of the code. Spend a few minutes checking wiring, connectors, and vacuum hoses first—those are cheaper and often the real issue.

Possible Fixes & Repair Costs

Typical repairs for P0108 range from very inexpensive DIY fixes to moderate shop bills. Cleaning and tightening a connector or replacing a small vacuum hose might cost you under $20 in parts. A new MAP sensor typically runs $40–$150 for most vehicles, plus 0.5–1.0 hour labor at a shop. Wiring repairs can range from $100–$300 depending on access and harness damage. In rare cases where the ECU is bad, you could be looking at $500–$1,200 or more. Costs depend on vehicle make, sensor location, and labor rates in your area.

• Clean and secure MAP connector terminals.
• Replace cracked or loose MAP vacuum hose.
• Repair or replace damaged MAP wiring (short to voltage or open circuit).
• Replace faulty MAP sensor with correct OEM-spec part.
• Repair shared 5V reference issues or replace another shorted sensor on the same circuit.
• Reflash or replace ECU only if proven faulty.

Can I Still Drive With P0108?

You can often still drive with P0108, but it’s not ideal. Many vehicles will run in a default or “limp” strategy, using backup values instead of accurate MAP data. That can mean poor fuel economy, rough running, and increased emissions. Short trips to get home or to a shop are usually okay if the car still runs reasonably well, but you should avoid long drives, towing, or hard acceleration until the issue is fixed.

What Happens If You Ignore P0108?

Ignoring P0108 can lead to long-term problems. Running rich for extended periods can foul spark plugs, clog the catalytic converter, dilute engine oil with fuel, and cause carbon buildup. You may also fail emissions testing and risk being stranded if the problem worsens or other components fail from the added stress.

Related Pressure Manifold Codes

Compare nearby pressure manifold trouble codes with similar definitions, fault patterns, and diagnostic paths.

• P0107 – Manifold Absolute Pressure/Barometric Pressure Circuit Low Input
• P0109 – Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent
• P0106 – Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance
• P0105 – Manifold Absolute Pressure/Barometric Pressure Circuit
• P0193 – Fuel Rail Pressure Sensor Circuit High
• P0103 – Mass or Volume Air Flow Circuit High Input

Key Takeaways

• P0108 means your ECU is seeing a MAP sensor signal that’s too high for current conditions.
• Common causes include a bad MAP sensor, wiring faults, connector corrosion, or vacuum hose problems.
• Symptoms often include poor fuel economy, rough idle, black smoke, and a strong fuel smell.
• Diagnosis should start with live data, visual inspection, and basic voltage checks before replacing parts.
• Most repairs are affordable if handled early; ignoring the code can damage other components over time.

Vehicles Commonly Affected by P0108

P0108 shows up across many brands because almost all modern engines use a MAP sensor. In the real world, it’s especially common on GM vehicles (Chevrolet, GMC, Buick), Chrysler/Dodge/Jeep/Ram models, and various Hyundai and Kia engines that use remote-mounted MAP sensors with vacuum hoses. It’s also seen on many Honda, Toyota, Ford, and VW/Audi vehicles, especially as wiring and connectors age or when aftermarket sensors are installed.

FAQ

Can a dirty air filter cause P0108?

A dirty air filter by itself usually does not cause P0108. It can affect airflow, but P0108 is specifically about high MAP sensor voltage. However, if the filter is so neglected that debris or oil gets into the intake and contaminates the MAP sensor, it can contribute to sensor failure or incorrect readings.

Is a MAP sensor the same as a MAF sensor?

No, they are different sensors. A MAP sensor measures manifold pressure (vacuum/boost) inside the intake manifold, while a MAF sensor measures the actual mass of air entering the engine. Some vehicles use one or the other, and some use both. P0108 is strictly a MAP-related code.

How do I know if my MAP sensor is bad and not the wiring?

You’ll need to test both. Check that the 5V reference and ground are correct, then measure the signal voltage and see if it responds smoothly to changes in engine vacuum. If the wiring checks out and the signal is stuck high or behaves erratically, the MAP sensor itself is likely bad.

Can I clear P0108 and keep driving if the car feels fine?

You can clear the code, but if the underlying issue still exists, P0108 will probably return. Even if the car feels okay now, running with incorrect MAP data can lead to long-term damage and poor fuel economy. It’s better to diagnose and fix the root cause rather than repeatedly clearing the code.

How long does it take to replace a MAP sensor?

On most vehicles, MAP sensor replacement is a quick job—often 15–30 minutes if it’s easily accessible on top of the engine. Some models with tight engine bays or remote-mounted sensors can take longer. A shop will typically book it as about 0.5–1.0 hour of labor, plus any diagnostic time.