View Full Version : thermostad and obd2 code
06-20-2008, 11:32 AM
hi i have recently hooked up an obd2 to my car and retrieved code po128 ( coolant thermostat, coolant temp below thermostat regulating temp) does this mean i need a new thermostat? if not what else could it be?
06-20-2008, 04:22 PM
does anyone have any advice>?
06-20-2008, 05:08 PM
id go ahead and replace the thermostat because it seems to be sticking open not letting the engine get up to operating temperature....
06-20-2008, 06:33 PM
Could also be a faulty water temp sensor. I'd replace the thermostat first to be sure, but if you have the money I'd replace them both to eliminate any possible malfunctions from either. Thermostat is $10 and coolant temp sensor is $15 from gm parts direct. Not expensive at all. Or get them from the local auto parts store.
06-20-2008, 11:03 PM
is there a how to on here as far as to swap the thermo and water temp sensor?
06-20-2008, 11:03 PM
oh and thanks by the way ill try both of those and let ya know what works.
06-20-2008, 11:06 PM
oh also i am getting codes po442 (evap control system leak.. and po420 (catalyst system effientcy below threshhold Bank 1) does any one know what this could be aswel..?
06-21-2008, 06:43 AM
The evap system is a vacuum line that runs back to the fuel tank from the intake manifold. It has a sensor that checks to make sure there is vacuum on it. If there is no vacuum it means there is a leak in the system somewhere that is letting fuel vapors escape to atmosphere. That code can pop up sometimes if your gas cap isn't tightened properly or if it's faulty, so check the gas cap first. Clear the code and if it comes back try replacing the gas cap. If it still comes back, there's a leak in the line somewhere else.
The other code could be related to the coolant temp problem. The pcm checks the rear O2 sensor to see if the catalytic converter starts working after a certain amount of run time. If your coolant temp is too low though and the engine isn't heating up enough, your exhaust gas temps could be pretty low and not letting the cat heat up fast enough, thereby failing the test and setting the code. Fix the coolant issues first, then clear all the codes and see if it comes back.
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