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Kenny , ASE Certified Technician
Category: Chevy
Satisfied Customers: 227
Experience:  Providing 16 years of experience with certifications in engine performance, electrical and brakes
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2003 Trailblazer LT: the Service Engine Soon light..PCM..dealership

Resolved Question:

I have a 2003 Trailblazer LT with ~125,000 miles on it currently.
A few years ago, I started noticing a ticking sound in my engine, a very high idle (sounded like a diesel engine) and occasionally, the Service Engine Soon light would come on. I had a mechanic read the error, and they told me the PCM needed to be reprogrammed, but could only be done by a dealership. So, after about 6 months, with the engine continuing to idle high enough for me to start getting worried, I took it to the dealership. At the time, I could only afford for them to re-program the PCM, but they also suggested replacing the fan clutch & relay.

A few months after that (in mid-February 2011), I had a mechanic replace the fan clutch (and also a new belt). The ticking sound and service light went away, but I still have very high idling and my AC only cools when I'm moving. (At stop lights or traffic jams, the cooling stops.) I've also noticed a decline in gas mileage performance, but I'm not sure if this is related.

I've researched this a bit on the web already, and the suggestions surround re-programming the PCM and replacing the fan clutch, which I've already done. I don't know where to go from here. Please help! Thanks ahead of time. :)
Submitted: 5 years ago.
Category: Chevy
Expert:  Kenny replied 5 years ago.
The pcm should be programmed with updated software the same time the fan clutch is replaced so the old software will not cause the new fan clutch to stay engage and may cause damage to the new fan clutch. After the updated software is programmed and the fan clutch is replaced you should also clean the throttle body. Carbon build up in the throttle body will cause the throttle plate to stick and cause the idle to be out of specification. This may also help fuel mileage after the throttle body is clean and the throttle plate can move freely.
Customer: replied 5 years ago.

The PCM was updated (according to the dealership) before I had the fan clutch replaced.

However, what you've described doesn't indicate that my AC problem will be solved. My AC doesn't cool when idling, only when moving. So therefore I have additional questions:


1.) Is the AC not cooling when idling related to the high idling (still sounds like a diesel engine rev)?

2.) What do I need to do to fix the problem with my AC not cooling when idling? I live in Atlanta, Georgia and it's quite hot here with lots of traffic, so my TB spends lots of time idling, so it makes it very uncomfortable.



Expert:  Kenny replied 5 years ago.
The fan clutch is what pulls the air through the A/C condenser that is mounted in front the radiator. At idle if the fan clutch is operating properly it will put the air through the condenser to allow the pressure in the a/c system to stay low enough for the compressor to stay on and cool inside the vehicle. When the fan clutch is not working at idle the compressor will turn of and stop cooling because it will build to much pressure. Will you or moving the air is flowing through the condenser so that is why it is cooling while driving. The fan clutch is stuck engaged causing a loud sound and poor a/c performance. The fan clutch will need to be replaced to fix your problem.
Kenny, ASE Certified Technician
Category: Chevy
Satisfied Customers: 227
Experience: Providing 16 years of experience with certifications in engine performance, electrical and brakes
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