Faulty thermostat causing SES light to illuminate on Chevrolet Trailblazer

Average mileage: 109,128 (14,000–215,159)
Engine affected: 4.2L 6 Cylinder
4 model years affected: 2003, 2005, 2006, 2007
10 people reported this problem
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problem details
2003 Chevrolet Trailblazer - 4.2L 6 Cylinder 84,000 mi,
This vehicle has a thermostat that fails in the open position which causes the temp gauge to drop below normal and heater to fail. The thermostat is located on the driver's side of the engine behind the alternator. You might need to remove the wheel to access the mounting bolts. You will need multiple rachet extensions and some patience. Dealer wants $500 to replace thermostat. Do it yourself for less than $100.
2005 Chevrolet Trailblazer - 4.2L 6 Cylinder 50,000 mi,
Replaced thermostat twice, dealer said it needed to be changed again or maybe it's just a bad sensor :-(
2006 Chevrolet Trailblazer - 4.2L 6 Cylinder 180,000 mi,
Ses light stays on. Had to replace multiple parts. Now it is the thermostat.
2003 Chevrolet Trailblazer - 4.2L 6 Cylinder 105,000 mi,
service engine light came on. was told it could need engine coolant or was the thermostat. let problem go with out doing anything. bout a year later had to have a catalytic converter replaced. do not ignore engine lights. cost way more down the road
2007 Chevrolet Trailblazer - 4.2L 6 Cylinder
Check engine light came on. Had it checked and code came back to thermostat
2005 Chevrolet Trailblazer - 4.2L 6 Cylinder 14,000 mi,
Ses light comes on after driving. The readout said coolant temperature
2003 Chevrolet Trailblazer - 4.2L 6 Cylinder 73,000 mi,
ought car used. When arrived home check engine light on. Check code- thermostat. replaced. no light or code
2003 Chevrolet Trailblazer - 4.2L 6 Cylinder 215,159 mi,
temp gauge read around 110 but the heat was hot . also check engine light was on
2007 Chevrolet Trailblazer - 4.2L 6 Cylinder 128,000 mi,
Had the same problem.
2003 Chevrolet Trailblazer - 4.2L 6 Cylinder 133,000 mi,
I actually had my thermostat replaced after a faulty reading