The MAP (manifold absolute pressure) sensor measures pressure inside the intake manifold, which tells the engine computer how much load the engine is under. Engines without a MAF sensor calculate airflow from the MAP reading (speed-density), while engines with a MAF use it as a cross-check and for barometric pressure. On turbocharged and supercharged engines the MAP sensor also reads boost. A bad MAP sensor causes poor fuel economy, black smoke, hesitation and codes such as P0106.
Bad MAP sensor symptoms
- Rich running: black smoke, fuel smell and poor fuel economy
- Hesitation or surging when accelerating; see car jerks when accelerating
- Rough idle or stalling; see rough idle
- Hard starting
- Boost control problems on boosted engines, such as underboost or overboost codes
MAP sensor codes
| Code | Meaning |
|---|---|
| P0106 | Range/performance |
| P0107 | Circuit low input |
| P0108 | Circuit high input |
| P0068 | MAP/MAF and throttle position disagree |
How to test a MAP sensor
- Key on, engine off: the MAP reading should equal barometric pressure, about 100 kPa (29 to 30 inches of mercury) near sea level and lower at altitude.
- At a warm idle: manifold pressure drops well below barometric because of engine vacuum; a typical healthy engine pulls roughly 17 to 21 inches of vacuum at idle.
- Snap the throttle: the reading should jump toward barometric (or above it, on boosted engines) and fall back quickly.
- Signal voltage on a common non-boosted sensor is low at idle (around 1 volt) and high near wide-open throttle (around 4.5 volts).
- Check the 5-volt reference and ground at the connector if the reading is stuck.
MAP sensors on boosted engines
A standard sensor reads up to about atmospheric pressure, so turbocharged and supercharged engines use 2-bar or 3-bar sensors that can read boost. If a supercharger or turbo is added to an engine, the MAP sensor range and the engine computer calibration must match, or fueling under boost will be wrong; see what does a supercharger do?.
MAP sensor vs MAF sensor
The MAF measures the mass of air entering the engine directly; the MAP measures pressure in the manifold. Many engines have both. See MAF sensor symptoms and cleaning.
What else causes MAP codes
- A split or disconnected vacuum hose to the sensor, on designs that use one
- Carbon blocking the sensor port in the intake
- A vacuum leak or mechanical problems such as incorrect valve timing that lower vacuum
- A shorted sensor sharing the 5-volt reference (P0641)
Low, unsteady vacuum with good sensors can mean worn rings, burnt valves or a jumped timing chain; a compression test tells you whether the engine itself is worn, and our engines page lists replacements by code.
Trouble codes: P0069 MAP/Barometric Correlation · P0105 MAP Sensor Circuit · P0129 Barometric Pressure Too Low · all OBD2 codes.
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