P0108 Code: MAP/Barometric Pressure Sensor Circuit High
The MAP signal is pinned near 5 volts, so the PCM sees impossibly high manifold pressure even at idle.
At a glance
Severity: Moderate
- Meaning
- MAP/Barometric Pressure Sensor Circuit High
- System
- Fuel & Air Metering · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $0–$900
- DIY difficulty
- Moderate
At idle a healthy non-turbo engine pulls manifold pressure down to roughly a third of outside air pressure, and the MAP signal sits around 1 to 1.5 V. P0108 sets when the signal stays above the upper limit, usually about 4.8 to 4.9 V, which would mean more pressure than the sensor is built to measure. The most common electrical reason is an open sensor ground, which lets the signal float up toward the 5-volt reference; a signal wire shorted to the reference or to a 12-volt circuit does the same. On turbocharged engines, a boost control fault that pushes pressure beyond the sensor's range can set P0108 under hard acceleration, and a lower-range sensor fitted by mistake maxes out at the first hint of boost.
Can I keep driving? The PCM falls back to a fixed pressure value, but some engines run noticeably rich in the meantime. Keep driving to a minimum if you see black smoke or smell fuel, and on turbo engines stay out of full throttle until overboost has been ruled out.
How to read P0108
- P Powertrain
- 0 Generic (SAE)
- 1 Fuel & air metering
- 08 Specific fault
Symptoms
- Check engine light on
- Black smoke, strong fuel smell and sooty tailpipe
- Rough idle and, over time, fouled spark plugs
- Sharp drop in gas mileage
- Turbo engines: code sets during hard acceleration, sometimes followed by reduced power
- Live data shows MAP at or above barometric pressure at idle
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Open sensor ground wire or corroded ground connection
- Signal wire shorted to the 5-volt reference or to a 12-volt circuit
- MAP sensor failed internally
- Water in the connector bridging reference and signal pins
- Overboost from a sticking wastegate or boost control fault (turbo engines)
- Wrong-range sensor installed, or vacuum hose off so a remote sensor reads atmospheric
- PCM input fault
Diagnosis step by step
Compare key-on and idle readings
Key on, engine off, MAP should equal barometric pressure, about 101 kPa near sea level. Start the engine: a non-turbo engine should drop to 25 to 35 kPa within a second. A signal of 4.9 to 5.0 V, or a pressure well above baro with the engine stopped, is electrical; a normal key-on value that simply doesn't drop at idle points at a disconnected vacuum hose or a mechanical problem.
Tools: OBD-II scanner
Check the sensor ground
Key on, back-probe the ground pin and measure against battery negative. It should read under 0.1 V. An open ground reads close to 5 V here, because the reference passes straight through the sensor to the ground pin with nowhere to go.
Tools: Multimeter
Unplug the sensor and watch the scanner
With the key on, disconnect the MAP sensor. Most PCMs pull the signal low when nothing is connected, so the reading should drop to its minimum and P0107 may set. If the reading stays high with the sensor unplugged, the signal wire is shorted to voltage in the harness.
Tools: OBD-II scanner, Multimeter
Verify the sensor type and hose
Match the part number to the engine: sensors for turbo engines cover two to three times atmospheric pressure and read only about 1.5 to 2 V at key-on, while a non-turbo sensor reads about 4.5 V. On remote-mounted sensors, make sure the vacuum hose is attached and not split.
Tools: Flashlight
On turbo engines, log boost against target
Graph actual MAP or boost against the PCM's desired boost during a hard pull in a safe place. If actual pressure overshoots target and runs into the sensor's maximum, inspect the wastegate actuator, its linkage and the boost control solenoid before blaming the sensor.
Tools: OBD-II scanner
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Repair sensor ground wire or ground point | Yes | $20–$150 |
| Dry and clean connector terminals | Yes | $0–$60 |
| Replace MAP sensor | Yes | $60–$250 |
| Repair shorted harness section | No | $120–$350 |
| Repair wastegate or boost control solenoid | No | $150–$900 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Field data
| Hyundai | 2 | Azera, Sonata |
|---|
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
State OBD-II emissions tests fail the vehicle while the check engine light is on. If the engine ran rich for a while, check for misfire or catalyst codes before going back, as they would also fail the test.
Frequently asked questions
Why does P0108 cause black smoke?
A maxed-out MAP reading tells the PCM the engine is at full load, so until it substitutes a default value it injects far more fuel than the engine needs. The unburned fuel shows up as black smoke, a strong smell and sooty spark plugs.
Can a disconnected vacuum hose set P0108?
On remote-mounted sensors, a hose that is off or split makes the sensor read outside air pressure at idle. Depending on the calibration, that sets P0106 or P0108, so always look at the hose before replacing the sensor.
My turbo car only sets P0108 at full throttle. Why?
Either boost is overshooting past the sensor's range because of a sticking wastegate or boost control fault, or the installed sensor has too small a range for the engine. Log boost against target to tell which.
Could a broken ground wire really cause a high reading?
Yes. The sensor divides its 5-volt reference between ground and signal. With no ground, nothing pulls the signal down, so it floats up close to 5 V, which is exactly what P0108 looks for.