1999 Chevrolet Express 3500 MAP Sensor Replacement Cost

The engine's computer has to receive input from many sensors, and ensure they are in agreement. An extremely important sensor that is used in reference to nearly all engine operations is the manifold absolute pressure (MAP) sensor. The MAP sensor records the air pressure in the intake manifold, and reports that information to the computer. This allows the computer to calculate, or confirm, the amount of air moving into the engine, amount of exhaust gas to expect, the amount of fuel to send into the engine, and many other important factors. Lastly, this sensor works very closely with the mass airflow (MAF) sensor to allow extremely accurate response to changing conditions.

When a MAP sensor fails, the vehicle may exhibit engine performance problems such as poor power, rough idle, poor fuel economy, and excessive tail pipe smoke. The Check Engine Light may illuminate and codes may set for a defective MAP sensor.

If the MAP sensor detects unexpected conditions, a few things happen. The engine's computer will trigger the check engine light, and the on-board diagnostic (OBD) trouble codes will reflect the air pressure conditions in the engine intake manifold. Also, depending on what pressure reading is present, the engine may compensate for these conditions, causing the engine to burn excessive amounts of fuel, sending black smoke from the exhaust pipe. In this case, the OBD trouble codes would also reference faults recognized by the exhaust oxygen sensors. The engine may also have issue with idling roughly, failing to start, stalling, hesitation, power loss, misfires, and fuel consumption. »MORE: How to tell if you have a bad MAP sensor

When the MAP sensor fails driving can be dangerous. As engine power may surge on and off, the vehicle may lurch forward. Overall engine performance may become unpredictable and difficult to control. It is preferred to tow the vehicle if any of the mentioned symptoms are present. If the vehicle operates normally or near normally, driving the vehicle should not cause any issues.

MAP sensors do tend to fail sometime in most vehicles. Failure rates are highest between 125,000 and 150,000 miles, independent of age. The sensors can also be damaged during air filter changes, and anytime the engine intake manifold is removed. Lastly, a collision may cause an electrical fault in the MAP sensor.

When the check engine light is on, and OBD trouble codes refer to the MAP sensor, the servicing technician will begin by inspecting the vehicle for any indication of physical damage before moving on with testing. A computerized scanner will be connected to the vehicle, and current conditions will be compared to current readings from the various sensors in the vehicle. When these conditions are compared, and analyzed, the technician relies on their classroom training to understand which component to test. Once one or more components are suspected of failure, the servicing technician will begin testing with the most likely component, until the issue has been verified through testing.

Replacing the MAP sensor is generally quick and easy. The sensor will typically be on or adjacent to the intake manifold, and the fastener may be a screw or clip. Once the sensor is replaced, the technician will review sensor data, and confirm the issue has been resolved.

Replacing a MAP sensor without a proper diagnosis may end in a failed repair attempt. Before replacing the sensor, a quality technician will first verify that the engine has normal vacuum readings, that there is no oil getting into the MAP sensor, and that the vacuum line or connection is in good condition.

We always recommend contacting the dealership parts department for revised part numbers. There may be a new part number for the manifold absolute pressure sensor, which can be a redesigned part that fixes known flaws. Aftermarket sensors may not have these updates,