Well, I'm stuck....

Yesterday evening my trusty 2003 blazer threw a SES light with no noticeable performance issues. Taking it to the local parts place, they pulled the code, it was a P0128 (Coolant temperature below threshold).

Searching the forums, I have tracked down this issue to a failed T-stat (which I just replaced this evening) or the sensor. I'm not a person to randomly throw money at a problem to see if it corrects the issue, but....

1) Replaced T-stat and insured coolant level was good. Two months ago, I flushed and filled my coolant per forum suggestions, no issues seen. Coolant is fine, its the orange stuff, but its fresh.

2) Temperature prior to T-stat replacement hovered at the "1st tick" (my guess 160'ish degrees) on my morning and evening commute (30 minute drive @ highway speeds).

3) After replacing my T-stat, the temp gauge goes just under 210 after about 10-15 mins of idle. This is a marked improvement, whereas my previous drive only showed ~ 160'ish. Replacement t-stat appears functional (showing a hair under 210).

The SES light is still lit, I have the truck lifted on the passenger side, filled up with coolant, (hopefully burped of air pockets). I disconnected the battery (but had key in ignition) No change, SES light still lit.

Per the forum search, my next step appears to be to replace the coolant temperature sensor, which isnt a big deal, I found some pictures ('because I'm not a professional) and the parts are cheaper than the dealer.

My question is that when searching for the sensor, there are approximately 4 available sensors. I have an "X" engine, no OHC, as generic as it gets, 2003 blazer w/4.3L twin push-rod design and 4x4 no auto 4xHi (really generic ride, no frills).


My current step is to have the engine totally cooled off with battery disconnected overnight to a) alllow coolant temp to go to ambient b) clear the code.

What sensor do I need, or is there something I overlooked:
Rockauto lists ACDELCO Part # 2134396 (SENSOR,ENG COOL TEMP 4 WHEEL DRIVE) and ACDELCO Part # 213928 ( {2-WAY MALE #15326386} SENSOR,ENG COOL TEMP ). I will go with OEM, I'm not going to futz around with some aftermarket sensor. $10 difference means do it right the first time.

Thanks for any feedback

 

Check the codes again now that you have replaced the T-stat. Disconnect the battery for atleast 15 minutes and see if it comes back. This code takes a few drive cycles to set and should not come back immediately.

 

Thanks, I was hoping you would chime in. I have the battery disconnected overnight and will check in the AM (in order to let the coolant to get to ambient temp). This one has been good as gold to me and since I dont have any undercarriage rust, I plan on running it into the ground.

Of course, I'm always open to other suggestions

 

How much did that sensor run ya?? My light came on yesterday too. So i got out my code reader and got the same code, my light went back out though and my Temp really hasn't changed its reading at all though, I think I will change the T-stat just to be safe. Rather do it now in decent weather rather than Mid winter out in the Driveway.

 

After changing the T-stat and letting the truck cool to ambient (overnight) the light went away immediately.

The sensor, looks to be ~ $20 + shipping from rockauto.com but I'm not 100% sure which one to get if I needed it.

 

I bought that sensor today at Autozone for $12.

 

I have the same P0128 Coolant Temperature Below Threshold code, and I have already replaced the thermostat and the coolant temperature sensor. I clear the code, and after a day or two of driving, it comes right back. The temperature does not seem to go above the 160-ish range as well. Any ideas what else could be the problem???

 

When you changed the sensor and T stat you most likley got air in there. Jack up front pass side, take radiator cap off and let in run for a bit with the heat on. If the coolant goes down you most likley got it.