Reduced engine power light on 02 trailblazer

I have a intermitenat problem with a reduced enegine power light and service engine light coming on when I press hard on the acceelarator. I can be traveling around town and push down to pass a car in the 35-40 mph range and both lights will come on and the engine power will drop have low power and RPMs will rise and oil pressure will go from 42 to 44. Temperature dose not apaper to change. I have ~ 80 k miles and have had regualr oil changes and service. I can shut engine off and the reduced power light often goes off but check engine remains on. Let car sit over night and start it up and many times the check engine light goes off. I have had it to local mechanic immedialy after a occurance but no code is registerd when checked(neither light was on when droped it off). and he says can’t help until osme thing goes wrong. What gives? There is no weather correlation and the only other thing I have noticed is that once starting up in the AM after this incident occured the 4 wheel drive switch will be binking and it sounds like a vacum line was leaking and it won’t enter gear unless I turn the switch and then the high pitched hiss dispates. At first I thought this was a tank of bad gas but have run another tank thorugh and still this problem comes up.

The problem is usually the throttle position sensor (TPS) or the throttle pedal assembly. Have your mechanic check this out. The TPS is a lot cheaper than the throttle pedal assembly. Neither one of these components leave a code all the time so it’s often difficult to diagnose.

Before you get to far into it check for bulletins.

Thanks I had not thought about this possibility. Can they determine if the senor is bad even when there are no idiot lights on or symptoms?

missileman is right about the common causes. I have an '04 TB and a good site for technical questions on this Trailblazer/Envoy platform is There have been numerous posts wrt your symptoms over there.

I don’t buy the lack of diagnostic info your mechanic is giving you. If the SES light and Reduced Engine Power lights illuminate, the ECM turned them on and has stored information about the error condition. It may take a more advanced scan tool like a TechII or similar to extract the freeze frame data or diagnostic codes but they will be there. There are specific codes for the gas pedal’s two position sensors and the companion sensors in the throttle body. If a mismatch occurs between any of them, the ECM sets a code and goes into reduced power mode.