Hi All,

My check engine light recently came on (1998 Chevy Blazer) and I plugged in my scanner and got the following codes P0108, P0121 and P0122. Not sure what I have to do to fix these and I believe they are related. Thanks for any help I can get.

 

P0108 - Manifold Absolute Pressure [MAP] Sensor Circuit High Voltage
P0121 - Throttle Position Sensor Circuit Range/Performance
P0122 - Throttle Position Sensor Circuit Low Voltage

A problem with the +5V reference from the PCM or either of these sensors could cause all of the codes that you are getting. The TPS sensor should output ~0.5V at closed throttle and ~4.5V at wide open throttle and should be a smooth transition between those values.

The MAP sensor outputs a voltage in response to the vacuum level in the intake. I have posted the normal atmospheric voltage outputs that should be expected in other threads and a search for "map+altitude" should turn that information up.

 

Welcome from New York.