2005 Chevy trail Blazer ,changed coolant temp sensor, and now #4 cylinder is misfiring


Asked by Ericman1967 Aug 25, 2019 at 02:58 PM about the 2005 Chevrolet Trailblazer LS 4WD

Question type: Maintenance & Repair

2005 Chevy trail Blazer had a code for engine
coolant temp sensor needs changed, at the time
the vehicle was running great,but changed it
because of the code. Pretty easy fix, had to remove
battery, belt, alternator , and sensor. A little bit of
coolant came out at removal. Replaced sensor and
resembled. Started driving and pretty quickly it
started running really rough! To the point that it
died. Started back up and drove home. Thinking
the new sensor was bad, I put the old sensor on . It
ran better but after a bit started running just a little
rough not near as bad as before! Also when I
replaced both sensors, new and old when running,
the check engine light started flashing , not just on
but flashing! So I took to have codes read and it
showed #4 cylinder is misfiring. Trying to find out
before I go replacing plugs and coils if mabey
since I took out battery if ecm needs reset, I'm
really at a loss. I know all the traditional reasons
why a cylinder would missfire but I need to know if
there is any reason related to replacing the temp

2 Answers


Thank you for your answer! The code was directly for the temp sensor, but its worth noting that the temp gage shows temp normal at about 200 deg. And the sensor is not located by anything that coolant could have leaked onto. this is the most expansive system (ECM) i have ever worked on. the coolant temp sensor controls everything from vac adv, full trim, fuel delivery,,all of those issues can cause a #4 cylinder issue, it was an easy fix ,to easy,lol, i can't see anything i could have gotten wet or have disturbed . if i cannot get a good answer i will just take it for diagnostic, it probably a coincidence that a coil when out at that very moment but want to make sure before i start replacing unnecessary parts!

1 people found this helpful.

Hi Eric, wondering if you had any rain prior to this happening? A very common problem is our hood seals will allow water to drop down onto the #4 cylinder. Look down with a mirror prior to taking plug out, dry it out. I use a long screwdriver with a paper towel or rag wedged in there. I used a long piece of weather stripping from depot, and ran it in front of the hood seal, problem solved. You're right, location on 05 of the sensor woudn't allow water up top, luckily it's not 06 and newer, Chevy moved sensor to passenger side way in the back, PIA to get to. If no rain, no water, yeah, swap coils from a different cylinder, see if the P0304 follows to the swapped cylinder. Could be coinkidink, never know.

1 people found this helpful.

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