I was driving my 2002 C5 Z06 (59,00 miles, stock) at VIR Monday and the check engine light came on. Using a code reader I got a MAP intermittent out of range reading. The car was running fine. I cleared the code and ran two sessions before it showed up again. Clearing it again I drove home 400 miles with no problems or check engine warnings.

Looking on line I see this could be a bad MAP sensor, vacuum leak or bad EGR valve.

Have any of you had this problem and if so how was it resolved?

Thanks.

George S.

 

Check the vacuum grommet, the harness and connector. Gm map sensors are not normally problematic. If you can get a scanner on it, it should read almost 5v with key on engine off.it should read about a volt at idle with a stock cam, higher with a performance cam.
When the engine is cold, you can run it and wiggle the harness and connector to see if the voltage jumps around. You might find it that way.
If you can graph it on he scanner or a lab scope, that would be best. If you don't find it, run the engine and watch the graph. Have someone hit the gas pedal quickly on and off. The graph should rise and fall smoothly if it's on the correct scale. If it spikes high, change the sensor.
Here is a description of the map operation.
The manifold absolute pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has a 5 volt reference circuit, a low reference circuit, and a signal circuit. The powertrain control module (PCM) supplies 5 volts to the MAP sensor on the 5 volt reference circuit. The PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the signal circuit which is relative to the pressure changes in the manifold. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The PCM should detect a high signal voltage at a high MAP, such as when the ignition is ON, with the engine OFF, or at a wide open throttle (WOT). Certain vehicle models will also use the MAP sensor in order to determine the barometric pressure (BARO). This occurs when the ignition switch is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range.

 

Thanks. That is the information I needed. Now I just need to see if my big hands an physically get to the sensor to check the vacuum line and connector..

 

There is no EGR valve on a C5.

 

No wonder I couldn't find it in my shop manual.

Thanks.

George S.