Code P0128

[tankerpilot01]

My 2002 Tahoe's Check Engine light came on yesterday...I plugged my code reader in and it was throwing a P0128 code. It said 2 codes, but both were the same code, but 2 of 2 had Pd next to the P0128. From what I've been able to gather online....is my thermostat stuck open? Just looking for any thoughts on this. If that is the issue, you guys recommend any certain brand of thermostat? I have a Be Cool aftermarket radiator (with built in engine oil cooler and transmission cooler). I asked Be Cool at the time I bought it if I should change and they guy said to stick with the factory thermostat....what is stock anyway? 190F? Thanks for your help!

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[EvansBlue]

Anything under 180 can cause problems with the PCM. You'd usually run a190 or 200. It could be that the thermostat is wanting to stick.

[ZX1100F1]

The stock T-stat is a 195F
How long ago did you replace the radiator?

[tankerpilot01]

The radiator was replaced this summer. I cleared the code and drove it to work (20 miles) and it didn't come on, it was on the drive back that it came back on again. So maybethe thermostat isn't stuck open all the time....just sticks periodically....????

[tankerpilot01]

So if that is the issue...you guys recommend to stay with the 195 degree?

[ZX1100F1]

You pretty much have little choice if you want to keep the master caution panel from lighting up.

11T3B or 11T2B?

[tankerpilot01]

Well...with some help from the guys at the auto hobby shop (I'm Air Force)....I think I figured out what is going on. Makes sense logically...but I've never had an issue before.

I have PermaCool dual electric fans and they turn on every 12 seconds for about 5 seconds (yes I timed it when I was trying to get the temp up), which doesn't allow the engine to come up to temp. I've noticed this driving...that the temp gauge is rarely above like 160 or so. So I pulled the fuse on the fans and the temp went up to the "more normal" 200 degree range. The guy there told me it is because when I have the defrost on, the fans cycle to keep the air conditioning compressor from over heating (I'm paraphrasing here....something about the condenser, etc).... So since I have the defrost on this time of year, the fans never let the engine temp come up. There is a wire (blue) that goes down to the compressor that tells the fans when the ac is on and that is what is turning the fans on. Not sure how that works, becasue inside, the AC light isn't on when in defrost??? Is it still on no matter what? The fans have been in for over 5 years and I've never seen this before.....mabye I've never driven when it is this cold....I don't know.....Does this sound like what is going on to you guys? I'm gonna call PermaCool tomorrow and see what they say.