The SES light comes on usually when I'm cruising on the freeway. It has also come on after going WOT on the freeway and when I let off it will come on. Also my milage has really decresed lately, down to 11 mpg, all around town driving though. It's not the oxygen sensor, I replaced that. It's not the thermostat I replaced the 160 with a 180. I do have one spark plug wire that is a little burnt from my headers.(Where can I buy one moroso wire?) Now I suspect it is the hypertech chip which I have heard nothing good about.(I didn't put it in the previous owner did) Would it be a good idea to replace it with the stock chip or some other chip? Please help me!

 

I think ??? that the code 45 referes to the egr valve, it only come into play a highway speeds or near WOT. I may be wrong about this so check on the board to see what it is

 

code 45 is definatly rich exhaust..

 

Does it have a relocated MAT? If so, that's your problem. The relocated MAT causes the calibrations to richen when it reads cooler temps. Many SD users have noticed this problem during winter. To use a relocated MAT with SD, you need to recalibrate the MAT tables in the eprom to make it give the proper fuel corrections.

Also, how is your CTS? If it is not working properly, it may be giving you a lower temp reading that it should and causing the mixture to be overly rich.

Overall, what is happening is, your ECM is giving too much fuel that can be corrected by the O2 sensor. The O2 sensor can only correct so much. Another problem may be that someone replaced the injectors and/or cranked up the fuel pressure too much (in combination with the other things I mentioned). Just think of ALL the reasons why you may have too much fuel, and double check them.

Though Hypertech eproms are not the best, by itself, it shouldn't be causing this problem. If it was, the Hypertech eprom would have started doing this from Day 1.

 

I don't have a relocated MAT. The problem probably is caused by the CTS because my car has never gone above 160 after replacing the thermostat. The CTS is on the driver's side on the block right? Do you have to drain the coolant to replace it? Thanks Glenn.