The Manifold Absolute Pressure (MAP) sensor is a critical component in modern fuel-injected vehicles. It plays a vital role in helping the Engine Control Module (ECM) determine the correct amount of fuel to inject for optimal performance and fuel efficiency. This article will delve into the function of the MAP sensor, why they fail, common symptoms of failure, and how to troubleshoot and replace a faulty MAP sensor.
How a MAP Sensor Works
Located on the intake manifold, often near the throttle body, the MAP sensor measures the air pressure inside the manifold. In turbocharged engines, it’s positioned before the turbocharger in the intake tract. The sensor contains a sealed chamber with a calibrated vacuum or pressure and a flexible silicon wafer (or chip) with an electrical current running through it.
When the ignition is turned on, the MAP sensor acts as a barometric pressure sensor, providing a reading to the ECM. Once the engine starts, the pressure in the intake manifold drops, creating a vacuum. As you accelerate, manifold pressure increases, reducing the vacuum. These pressure fluctuations cause the silicon wafer to flex, changing the electrical resistance and signaling the ECM to adjust fuel injection accordingly.
The ECM uses MAP sensor readings, along with data from the Intake Air Temperature (IAT) sensor, Engine Coolant Temperature (ECT) sensor, barometric pressure reading, and engine speed (RPM) to calculate air density and determine the optimal air-fuel mixture.
Causes of MAP Sensor Failure
MAP sensors, like other electrical components, are susceptible to contamination. A clogged or leaking vacuum hose (if applicable) can prevent accurate pressure readings. Excessive vibration can loosen connections or cause external damage. High engine temperatures can melt or crack electrical connectors. Any of these issues can necessitate MAP sensor replacement.
Recognizing a Failing MAP Sensor
A malfunctioning MAP sensor disrupts the engine’s air-fuel ratio, leading to improper ignition timing and potential engine damage. Here are some warning signs:
- Rich Air-Fuel Mixture: Rough idle, poor fuel economy, slow acceleration, strong gasoline smell (especially at idle).
- Lean Air-Fuel Mixture: Surging, stalling, lack of power, hesitation on acceleration, backfiring through the intake, overheating.
- Detonation and Misfire: Engine knocking or pinging sounds, loss of power.
- Failed Emissions Test: Higher than acceptable emissions levels.
- Check Engine Light: Illumination of the check engine light on the dashboard.
Common MAP Sensor Fault Codes
These are some common OBD-II codes related to MAP sensor issues:
- P0068: MAP/MAF – Throttle Position Correlation
- P0069: Manifold Absolute Pressure – Barometric Pressure Correlation
- P0105: MAP Circuit Malfunction
- P0106: MAP/Barometric Pressure Circuit Range/Performance Problem
- P0107: Manifold Absolute Pressure/Barometric Pressure Circuit Low Input
- P0108: MAP Pressure Circuit High Input
- P0109: MAP / Baro Pressure Circuit Intermittent
- P1106: MAP/BARO Pressure Circuit Range/Performance Problem
- P1107: Barometric Pressure Sensor Circuit Low Voltage
Note: These codes can sometimes be triggered by other issues. Always test the MAP sensor to confirm it’s the source of the problem.
Troubleshooting a MAP Sensor
Before testing, visually inspect the MAP sensor, connector, wiring, and vacuum hose (if applicable) for damage, loose connections, corrosion, and contamination.
To test with a multimeter and vacuum pump:
- With the engine off and battery on, check battery voltage (around 12.6V).
- Consult your vehicle’s service manual for wire identification (signal, ground, 5V reference).
- With the ignition on (engine off), check voltages: 4.5-5V (reference), 0V (ground), 0.5-1.5V (signal – non-turbo), 2.0-3.0V (signal-turbo).
- Start the engine and check signal voltage: 0.5-1.5V (non-turbo), 2.0-2.5V (turbo).
- With the ignition on and engine off, disconnect the MAP sensor vacuum hose.
- Connect a vacuum pump and monitor signal voltage while increasing vacuum. The voltage should steadily decrease.
Erratic or significantly different voltage readings indicate a faulty MAP sensor.
Replacing a Faulty MAP Sensor
Consult your vehicle’s service manual for specific instructions. Generally:
- Locate the MAP sensor.
- Remove securing screws/bolts.
- Disconnect the electrical connector and vacuum hose (if applicable).
- Compare new and old sensors.
- Install the new sensor and reconnect everything.
- Double-check all connections.
A diagnostic tool may be needed to reset the check engine light.
