# P0108: Manifold Absolute Pressure/Barometric Pressure Circuit High **Verdict:** Drive to a shop this week Air intake - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $100-$400 - **Urgency:** This week - **Most likely:** Failed MAP sensor or open ground wire - **DIY?:** Steps 1-3 ## Quick answer P0108 means the voltage on the manifold absolute pressure (MAP) sensor signal wire is above the range the engine computer accepts. That reads as extreme manifold pressure, beyond anything the engine can make. A failed sensor, a broken or corroded ground, moisture in the connector or a signal wire shorted to voltage are the usual causes. ## What does P0108 mean? The MAP sensor turns intake manifold pressure into a voltage signal. The engine computer supplies 5 volts and a ground, and the signal rises as manifold pressure rises: low voltage at high vacuum during idle and coasting, higher voltage at wide-open throttle or with the key on and engine off. The computer uses the signal to estimate engine load for fuel and spark, and on many engines to learn barometric pressure. P0108 sets when the signal stays above a calibrated maximum, usually close to the 5-volt reference itself, for a few seconds. A reading that high suggests the signal is seeing reference voltage through a broken ground or a short, or that the sensor has failed internally. Many makers set it on the first trip. Because high MAP looks like heavy load, the engine can run rich until the computer switches to a backup value. ## What are the symptoms of P0108? - Check engine light on - Black smoke or a strong fuel smell from the exhaust - Noticeably worse fuel economy - Rough idle or stalling - Sluggish acceleration ## What causes P0108? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Failed MAP sensor** (most common). When the sensor's internal circuit fails, its output can stick near the reference voltage. Heat, vibration and age are the usual reasons, and oil vapor contamination can contribute. If the ground and reference test good at the connector but the signal stays high with the hose connected and the engine idling, the sensor itself is at fault. 2. **Open or poor sensor ground** (common). If the ground wire breaks or a ground terminal corrodes, the sensor output floats toward the reference voltage and the computer sees a high reading. Corroded engine-to-body ground straps can also add resistance. Measuring voltage drop across the ground circuit while the engine runs finds poor grounds that look fine on an ohmmeter. 3. **Moisture or corrosion in the connector** (common). Moisture inside the connector can bridge terminals and create a path between the reference and signal pins, pushing the voltage up. Green corrosion, a missing seal or a cracked connector housing are clues. The fault often comes and goes with rain or after washing the engine, and cleaning or replacing the connector fixes it. 4. **Signal wire shorted to voltage** (less common). A signal wire that rubs through and touches the 5-volt reference wire, or another powered wire in the same harness, pushes the signal high. Melted harness sections near exhaust parts and poor repairs where wires were spliced together are typical. With the sensor unplugged, voltage on the signal wire that should not be there points to a short. 5. **Engine computer input fault** (rare). An internal fault in the engine computer's MAP input can read high even with good wiring and a working sensor. It is rare and is the last item checked, after confirming correct voltages at both ends of the harness. Look for water damage near the computer and any software updates for the vehicle first. ## How do you diagnose P0108? 1. Read MAP voltage with the key on; a value near 5 volts confirms a high-circuit fault rather than real pressure. 2. Inspect the connector for moisture, corrosion and damaged seals, and reseat it. 3. Unplug the sensor and check the signal wire for voltage that should not be there. 4. Measure ground voltage drop and the 5-volt reference at the connector with the engine running. 5. If the wiring checks out, replace the MAP sensor and verify readings at idle and with the throttle snapped. ## How do you fix P0108, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Repair ground, wiring or connector | $100-$400 | Includes cleaning grounds or replacing a corroded connector pigtail. | | Replace MAP sensor | $100-$350 | The usual fix once the wiring tests good. | ## Is it safe to drive with P0108? > **Drive to a shop this week.** It is usually safe for short trips, but the engine may run rich, waste fuel and stall at idle. Long-term rich running can foul spark plugs and overheat the catalytic converter, so get it fixed within a week or two, sooner if you smell fuel or see black smoke. ## Will P0108 fail an emissions test? P0108 keeps the check engine light on, which fails an OBD-II emissions test in most states. A MAP signal reading high can make the engine run rich, raising carbon monoxide and hydrocarbon readings in places that still test the tailpipe. After the repair, let the readiness monitors complete with several days of driving before testing. ## After the repair: clearing P0108 Clear the code and confirm on a scan tool that MAP reads near barometric pressure with the key on, then drops to a low, steady value at warm idle. Fuel trims should settle toward zero within a few drives as the computer relearns. If the black smoke or fuel smell is gone and P0108 stays away, the fix worked. ## How to prevent P0108 - Check the MAP connector seal and latch whenever intake parts are removed or replaced. - Keep engine ground straps clean and tight, especially on older cars in road-salt states. - Route wiring away from exhaust parts and replace missing harness clips after repairs. - Avoid twist-on splices on sensor wires; insist on proper soldered or crimped, sealed repairs. ## Codes often seen with P0108 - [P0106](/codes/p0106): Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance - [P0107](/codes/p0107): Manifold Absolute Pressure/Barometric Pressure Circuit Low - [P0172](/codes/p0172): System Too Rich (Bank 1) - [P0101](/codes/p0101): Mass or Volume Air Flow "A" Circuit Range/Performance - [P0420](/codes/p0420): Catalyst System Efficiency Below Threshold (Bank 1) ## Frequently asked questions ### Can I drive with a P0108 code? Yes, you can usually drive with P0108 for short trips. The engine may run rich, idle rough or stall, and fuel economy often drops. Do not ignore it for long, because rich running can foul spark plugs and overheat the catalytic converter, which costs far more than a MAP sensor. ### What does MAP sensor circuit high mean? Circuit high means the MAP sensor's signal voltage is above the range the engine computer accepts, usually close to the 5-volt supply. That would mean impossibly high manifold pressure. The computer concludes the sensor, its ground or its signal wire has a fault and switches to a backup value. ### What causes P0108? A failed MAP sensor is the most common cause of P0108. An open or corroded ground wire and moisture or corrosion in the connector are also common. Less often, the signal wire is shorted to the 5-volt reference or another powered wire, and an engine computer fault is rare. ### How much does it cost to fix P0108? Most P0108 repairs cost $100 to $400 at an independent shop. A MAP sensor typically runs $100 to $350 installed. Repairing a broken ground, a chafed wire or a corroded connector costs $100 to $400, depending on how long it takes to trace the fault. ### Can P0108 cause black smoke? Yes, P0108 can cause black smoke. A MAP signal reading high tells the computer the engine is under heavy load, so it adds extra fuel. The excess fuel burns incompletely and leaves soot. You may also smell fuel and notice worse mileage until the problem is fixed. ### Can a disconnected MAP vacuum hose cause P0108? A disconnected hose usually sets P0106 rather than P0108, because the sensor then reads outside air pressure, which is still within its normal voltage range. P0108 needs a voltage near the top of the scale, which points more to wiring, a ground problem or a failed sensor. Check the hose anyway. ### Can I fix P0108 myself? Often, yes. Inspecting the connector, cleaning corrosion and replacing the MAP sensor are manageable jobs with basic tools. A multimeter lets you check the reference, ground and signal voltages before buying a sensor. Tracing a short inside the harness can take time, so a shop may be faster for that part. ### Will P0108 affect gas mileage? Yes, P0108 usually makes gas mileage worse. When the MAP signal reads high, the computer thinks the engine needs more fuel than it does. Some engines limit the effect by switching to a backup value, but most drivers still notice more frequent fill-ups until the fault is fixed. ### Why does P0108 come and go in wet weather? P0108 that appears in rain or after washing the engine usually means water is getting into the MAP connector or a damaged section of wiring. Moisture can bridge terminals and push the signal voltage high. Inspect the connector seal and the harness for cracks, and replace damaged parts. ### Should I replace the MAP sensor for P0108? Replace the MAP sensor only after checking its ground, 5-volt reference and signal wiring. A failed sensor is the most common cause, but a broken ground or a short gives the same code, and a new sensor will not fix it. Ten minutes with a multimeter can save the cost of an unneeded part. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) - [EPA: On-Board Diagnostics (OBD)](https://www.epa.gov/state-and-local-transportation/vehicle-emissions-board-diagnostics-obd) ## Other air intake codes - [P0101 Mass or Volume Air Flow "A" Circuit Range/Performance](https://diagxcar.com/codes/p0101) - [P0102 Mass or Volume Air Flow "A" Circuit Low](https://diagxcar.com/codes/p0102) - [P0106 Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance](https://diagxcar.com/codes/p0106) - [P0107 Manifold Absolute Pressure/Barometric Pressure Circuit Low](https://diagxcar.com/codes/p0107) - [P0112 Intake Air Temperature Sensor 1 Circuit Low (Bank 1)](https://diagxcar.com/codes/p0112) - [P0113 Intake Air Temperature Sensor 1 Circuit High (Bank 1)](https://diagxcar.com/codes/p0113) - [P0117 Engine Coolant Temperature Sensor 1 Circuit Low](https://diagxcar.com/codes/p0117) - [P0118 Engine Coolant Temperature Sensor 1 Circuit High](https://diagxcar.com/codes/p0118) - [P0121 Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance](https://diagxcar.com/codes/p0121) - [P0122 Throttle/Pedal Position Sensor/Switch "A" Circuit Low](https://diagxcar.com/codes/p0122) ## Symptoms - [Why is black smoke coming from my exhaust?](https://diagxcar.com/symptoms/black-smoke-from-exhaust) - [Why is my car getting bad gas mileage?](https://diagxcar.com/symptoms/poor-gas-mileage) - [Why is my car idling rough?](https://diagxcar.com/symptoms/rough-idle) - [Why does my car smell like gas?](https://diagxcar.com/symptoms/car-smells-like-gas) --- Source page: https://diagxcar.com/codes/p0108 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.