The MAP sensor is used as an input to the Powertrain Control Module (PCM). It contains a silicon based sensing unit to provide data on the manifold vacuum that draws the air/fuel mixture into the combustion chamber. The PCM requires this information to determine injector pulse width and spark advance. When manifold absolute pressure equals Barometric pressure, the pulse width will be at maximum.
A 5-volt reference is supplied from the PCM and returns a voltage signal to the PCM that reflects manifold pressure. The zero pressure reading is 0.5V and full scale is 4.5V. For a pressure swing of 015 psi, the voltage changes 4.0V. To operate the sensor, it is supplied a regulated 4.8 to 5.1 volts. Ground is provided through the low-noise, sensor return circuit at the PCM.
The MAP sensor input is the number one contributor to fuel injector pulse width. The most important function of the MAP sensor is to determine barometric pressure. The PCM needs to know if the vehicle is at sea level or at a higher altitude, because the air density changes with altitude. It will also help to correct for varying barometric pressure. Barometric pressure and altitude have a direct inverse correlation; as altitude goes up, barometric goes down. At key-on, the PCM powers up and looks at MAP voltage, and based upon the voltage it sees, it knows the current barometric pressure (relative to altitude). Once the engine starts, the PCM looks at the voltage again, continuously every 12 milliseconds, and compares the current voltage to what it was at key-on. The difference between current voltage and what it was at Key On is the manifold vacuum.
During key-on (engine not running) the sensor reads (updates) barometric pressure. A normal range can be obtained by monitoring a known good sensor.
As the altitude increases, the air becomes thinner (less oxygen). If a vehicle is started and driven to a very different altitude than where it was at key-on, the barometric pressure needs to be updated. Any time the PCM sees Wide Open Throttle (WOT), based upon Throttle Position Sensor (TPS) angle and RPM, it will update barometric pressure in the MAP memory cell. With periodic updates, the PCM can make its calculations more effectively. The PCM uses the MAP sensor input to aid in calculating the following:
The MAP sensor signal is provided from a single piezo-resistive element located in the center of a diaphragm. The element and diaphragm are both made of silicone. As manifold pressure changes, the diaphragm moves causing the element to deflect, which stresses the silicone. When silicone is exposed to stress, its resistance changes. As manifold vacuum increases, the MAP sensor input voltage decreases proportionally. The sensor also contains electronics that condition the signal and provide temperature compensation.
The PCM recognizes a decrease in manifold pressure by monitoring a decrease in voltage from the reading stored in the barometric pressure memory cell. The MAP sensor is a linear sensor; meaning as pressure changes, voltage changes proportionately. The range of voltage output from the sensor is usually between 4.6 volts at sea level to as low as 0.3 volts at 26 in. of Hg. Barometric pressure is the pressure exerted by the atmosphere upon an object. At sea level on a standard day, no storm, barometric pressure is approximately 29.92 in Hg. For every 100 feet of altitude, barometric pressure drops .10 in. Hg. If a storm goes through it can change barometric pressure from what should be present for that altitude. You should know what the average pressure and corresponding barometric pressure is for your area.
Removal & Installation
- Disconnect electrical connector at sensor.
- Clean area around MAP sensor.
- Remove 2 sensor mounting screws.
- Remove MAP sensor from intake manifold.
- Check condition of sensor O-ring.
- Clean MAP sensor mounting hole at intake manifold.
- Check MAP sensor O-ring seal for cuts or tears.
- Position sensor into manifold.
- Install MAP sensor mounting bolts (screws). Tighten screws to 25 inch lbs. (3 Nm).
Connect electrical connector.
- Remove air cleaner duct and air resonator box at throttle body.
- Remove MAP sensor mounting bolt (screw).
- While removing MAP sensor, slide the rubber L-shaped fitting from the throttle body.
- Remove rubber L-shaped fitting from MAP sensor.
- Install rubber L-shaped fitting to MAP sensor.
- Position sensor to throttle body while guiding rubber fitting over throttle body vacuum nipple.
- Install MAP sensor mounting bolt (screw). Tighten screw to 25 inch lbs. (3 Nm).
Install air cleaner duct/air box.
- Start the engine and allow it to reach normal operating temperature. Using a diagnostic scan tool, check for the presence of any Diagnostic Trouble Codes (DTCs). Record and address these codes as necessary.
- Refer to any Technical Service Bulletins (TSBs) that may apply.
- Review the scan tool Freeze Frame information. If possible, try to duplicate the conditions under which the DTC set.
- With the engine running at normal operating temperature, monitor the scan tool parameters related to the DTC while wiggling the wire harness. Look for parameter values to change and/or a DTC to set. Turn the ignition off.
Visually inspect the related wire harness. Disconnect all the related harness connectors. Look for any chafed, pierced, pinched, partially broken wires and broken, bent, pushed out, or corroded terminals. Perform a voltage drop test on the related circuits between the suspected inoperative component and the ECM.
CAUTIONDo not probe the ECM harness connectors. Probing the ECM harness connectors will damage the ECM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.
- Inspect and clean all ECM, engine, and chassis grounds that are related to the most current DTC.
- If numerous trouble codes were set, use a wire schematic and look for any common ground or supply circuits.
- For any Relay DTCs, actuate the Relay with the scan tool and wiggle the related wire harness to try to interrupt the actuation.
- For intermittent Evaporative Emission trouble codes perform a visual and physical inspection of the related parts including hoses and the Fuel Filler cap.
- Use the scan tool to perform a System Test if one applies to failing component. A co-pilot, data recorder, and/or lab scope should be used to help diagnose intermittent conditions.