Troubleshooting a MAP Sensor

MAP sensor element
  • 1-2 hours
  • Intermediate
  • 35-125
What You'll Need
VOM (volt/ohmmeter)
Vacuum pump
Tool kit
Service manual
New MAP sensor
What You'll Need
VOM (volt/ohmmeter)
Vacuum pump
Tool kit
Service manual
New MAP sensor

Manifold absolute pressure (MAP) sensors sample and send information about the absolute pressure in the intake manifold to an automobile’s electronic control module (ECM) to help it control all the parameters necessary for efficient engine operation. The pressures they measure are usually the result of a vacuum, instead of positive force, though there are some supercharged or turbocharged vehicles. This is why it is referred to as "absolute pressure," as it can be pressure or vacuum.

Fuel injection duration, ignition timing, and in some autos, the valve timing and duration are all controlled by the ECM. The MAP sensor contributes its input to the ECM, which in turn controls many engine functions, including the fuel injectors.

Faulty MAP Sensor Indications

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MAP sensor problems can manifest in many ways. Symptoms include excessive fuel consumption, bad idle, power loss, hard starting, and even a no-start condition.

In the newest automobiles, the automatic transmission control can be affected by the MAP sensor. If it malfunctions in a way that leads to lean fuel conditions, your engine can overheat, experience detonation knocks and overheating, and suffer power loss and low performance. MAP sensors are usually reliable, but any mechanical/electrical component can fail with age and use.

MAP Sensor Location

The MAP sensor can be located on the intake manifold, slightly embedded in the manifold, as an integral part of the ECM, or just secured to an auto firewall and connected to the intake manifold with a length of flexible hose and to the ECM via the wiring harness. The service manual will help you find and identify the MAP sensor.

MAP sensor

Testing

Each vehicle brand has a specific set of parameters the MAP sensor operates under, so a specific service manual for your particular vehicle is needed to troubleshoot and repair/replace the MAP sensor properly. By following the test procedures outlined in the service manual and using your VOM (volt/ohmmeter), you can ascertain if the MAP sensor is faulty or if the problem is elsewhere, such as the wiring harness. Some OBD II testers will test the MAP sensor while the engine is running, negating the need to test for volts and ohms using a multi-tester.

Using a multi-tester to test the MAP sensor, you may be able to back probe the wiring harness plug using a small paper clip straightened so you can insert one end of the paper clip into the back of the harness plug to contact the wire inside. Follow the instructions in the service manual to make these tests checking both for volts and resistance. A handheld vacuum pump will aid in the process of testing the MAP sensor under varying conditions.

If your MAP sensor is of the type that is connected to the intake manifold via a flexible hose, check the hose for any cracks and breaks that would cause air leakage and, therefore, erroneous readings. Replace the hose if necessary.

MAP sensor viewed from connector end

Replacing MAP Sensor

MAP sensors are not easily repaired, so they're usually replaced to expedite the repair. MAP sensors are not costly, and they're usually simple to replace. You must take care when removing the old MAP sensor, as the fasteners are very small and can be easily broken. A squirt of penetrating oil on each fastener before attempting to remove it is highly recommended. Get the penetrating oil into the threaded portion of the fastener and wait a few minutes for the penetrating oil to work before removing the fastener.

Carefully unplug the wiring harness and plug in the new MAP sensor and reattach it in the position where you removed the old one. Reconnect any flexible hoses you disconnected previously.

MAP sensor

Verify it Works

After replacing the MAP sensor, start the engine and check for proper operation of the MAP sensor. If the problems have gone away, you have been successful in your endeavor. If you still have problems, then you will need to look elsewhere to find and solve them.

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