Engine Temp Sensor and Thermostat

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   Here's the latest. 

I experienced several instances of the fans coming on and getting the 127C reading over the last couple of months.  In each case the reading and associated fan activity would happen just as the car was reaching operating temp first thing in the morning (e.g.,75C after 15 mins of driving - which seems too long to come up to temp as well). On a few occasions I was just getting onto the highway when things happened - the car was just shy of op temp and I was  picking up speed (and the associated cooling effect). I would get the 127 code, the temp gauge would drop (thermostat wide open?), the fans would come on, and then after a minute or 2 the temp gauge would come back up to half way. I would clear codes and things would be fine until I did the same routine again. A couple of times I got 19537 - Engine Temperature too Low P3081 - 35-00 when trying to clear to the original cooling system fault and would have to clear a few times to get the fans to go off.

So the question is... is it more likely the G62 or thermostat?  What makes me think the thermostat is the time it takes to get the car warm, unless that could also be caused by a faulting temp sensor. What makes me think the g62 is the 127 reading.  Are we sure we can't get a 127 reading from some other system issue (i.e., thermostat faulting out and triggering fans, and sending signals to the ECU?).  

Any and all thoughts welcome.  Thanks.

Car still takes time (15 mins or so) to come to full operating temperature.  

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rock Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 09-Mar-2009 Online Status: Offline Posts: 13	Quote Reply Topic: Engine Temp Sensor and Thermostat Posted: 12-Jun-2010 at 02:04
	Here's the latest. I experienced several instances of the fans coming on and getting the 127C reading over the last couple of months. In each case the reading and associated fan activity would happen just as the car was reaching operating temp first thing in the morning (e.g.,75C after 15 mins of driving - which seems too long to come up to temp as well). On a few occasions I was just getting onto the highway when things happened - the car was just shy of op temp and I was picking up speed (and the associated cooling effect). I would get the 127 code, the temp gauge would drop (thermostat wide open?), the fans would come on, and then after a minute or 2 the temp gauge would come back up to half way. I would clear codes and things would be fine until I did the same routine again. A couple of times I got 19537 - Engine Temperature too Low P3081 - 35-00 when trying to clear to the original cooling system fault and would have to clear a few times to get the fans to go off. So the question is... is it more likely the G62 or thermostat? What makes me think the thermostat is the time it takes to get the car warm, unless that could also be caused by a faulting temp sensor. What makes me think the g62 is the 127 reading. Are we sure we can't get a 127 reading from some other system issue (i.e., thermostat faulting out and triggering fans, and sending signals to the ECU?). Any and all thoughts welcome. Thanks. Car still takes time (15 mins or so) to come to full operating temperature.

VWAffe Members Profile Send Private Message Find Members Posts Add to Buddy List Super Poster Joined: 26-Mar-2007 Location: Dayton, OH Online Status: Offline Posts: 470	Quote Reply Posted: 15-Mar-2010 at 01:05
	To be thorough, the dealer (or you) could compare the G62 reading against the actual engine temperature - both what the ECU says, and check the resistance across G62 at that temp. (There's an Ohm vs. Temperature chart in the Bentley.) If G62 is correct, either the ECU is bad (telling the thermostat to open when it shouldn't), or the thermostat is actually stuck open. VAG-COM can be used to monitor what the ECU is commanding the thermostat to do... not sure the dealer techs normally know how to do that, or will go to that level of detail. When it's your own money, you tend to want to diagnose things correctly the first time... a good motivator, when a bad t-stat will cost $400 to DIY. Let us know how it goes!
	His: '03 W8 Sedan 6MT ..."it goes to 11!" Hers: '02 V6 Wagon 4Motion ...both black on black w/ limo tint

yesimalex Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 19-Nov-2008 Location: Berkeley Spring Online Status: Offline Posts: 373	Quote Reply Posted: 14-Mar-2010 at 04:00
	Keep posting please. I'm throwing the cooling performance code but not the engine temp code. I'd like to hear more about this. I.e. I don't have a vagcom :D
	Dual Magnaflows and Level 10 bullet proof TC Turbo DIY You just got burnt by a wagon with two car seats in the back....

rock Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 09-Mar-2009 Online Status: Offline Posts: 13	Quote Reply Posted: 12-Mar-2010 at 00:49
	Thanks for the reply. Last time the fans went full blast I got some hard faults and they were: 18613 - Performance Malfunction in Cooling System P2181; and 19537 - Engine Temperature too Low P3081 Interestingly, even with fans back to normal (fault codes cleared) the car seems to heat up slowly (i.e., 15 mins to reach operating temp). I occasionally monitor the engine temp via the climatic control diagnostic and it typically stays around 75C in town - has gotten up to 85 on the highway. I now have a vag-com and will runs some other tests. I hope it is simply the G62 (although it was replaced last year) vs the thermostat. Dealer says thermostat but I am not convinced.

yesimalex Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 19-Nov-2008 Location: Berkeley Spring Online Status: Offline Posts: 373	Quote Reply Posted: 11-Mar-2010 at 23:51
	Wow you just summed up a problem in one post. Not just that.. you posted GOOD diagnostic skills. Much praise and admiration dear sir!
	Dual Magnaflows and Level 10 bullet proof TC Turbo DIY You just got burnt by a wagon with two car seats in the back....

VWAffe Members Profile Send Private Message Find Members Posts Add to Buddy List Super Poster Joined: 26-Mar-2007 Location: Dayton, OH Online Status: Offline Posts: 470	Quote Reply Posted: 11-Mar-2010 at 04:10
	A shorted G62 will make the displayed temp show 127C - nothing else will, outside of a bad wire or a bad ECU, which are unlikely. The 127C display is coming from the ECU, which gets its readings from G62. G83 is the fan switch, IIRC - it could also cause the fans to run constantly, but you wouldn't see 127C from the ECU. A stuck open tstat wouldn't run the fans all the time. A faulty tstat heater also can cause it to run fans when not needed, but not display 127C. Look for a flaky G62. You can check G62 manually with a multimeter - shorted or open is bad. That would also explain why the motor isn't warming up; the ECU is running the fans on full throttle, thinking the engine is way hotter than it is. Be glad; on the 30V V6, it won't even start when G62 shorts out. You'd be best served by having your own VAG-COM and not relying on the dealer... at least that's how I roll. Cheers!
	His: '03 W8 Sedan 6MT ..."it goes to 11!" Hers: '02 V6 Wagon 4Motion ...both black on black w/ limo tint

02passatw8 Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 27-Oct-2007 Location: Framingham Online Status: Offline Posts: 379	Quote Reply Posted: 10-Mar-2010 at 06:13
	Sounds like the tstat is sticking open that is why your car is cooling so fast. Once i a while my car does the same things and after a few days the fans go off and it resets.

yesimalex Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 19-Nov-2008 Location: Berkeley Spring Online Status: Offline Posts: 373	Quote Reply Posted: 10-Mar-2010 at 05:51
	Ok I know long since posted but, For what it's worth my dealer is looking into this issue on my car. He already checked the sensors and said they looked in good shape, but he wants to do some scans while the car is running. He said usually it's just replaced the temp sensors AND the control unit. We'll see.
	Dual Magnaflows and Level 10 bullet proof TC Turbo DIY You just got burnt by a wagon with two car seats in the back....

rock Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 09-Mar-2009 Online Status: Offline Posts: 13	Quote Reply Posted: 16-Nov-2009 at 21:12
	I should also mention that the tech at the dealer checked the coolant temp and it measured 33 C (after 15 min run time - apparently should have been 90) and then verified the temp with a non-contact thermometer.

rock Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 09-Mar-2009 Online Status: Offline Posts: 13	Quote Reply Posted: 16-Nov-2009 at 20:45
	I appreciate there are some other threads on this but I need some clarification based on what has been posted to date. If channel 45 shows 127 °C, is that confirmation that the G62 sensor (as opposed to G83 or thermostat) is bad and needs replacement (and is the cause of the fans being on constantly)? Or can you be getting the 127 reading based a bad tsat or G83 or other cause? FYI - both of my temp sensors have been replaced in the last 2 years, but the fans are back on constant. Took to dealer to scan and clear faults. They indicated that the code indicated an issue with cooling system performance and assume it is the tsat because the sensors have been replace previously. I am not convinced it is tsat based on the climatic diagnostic reading of 127. After the faults were cleared worked fine for a couple of days then fans back but no CEL. Takes 10-15 mins for temp gauge to come up to normal but goes back to 0 after a short stop and restart - then takes another 10-20 mins for gauge to come back to normal (and is not gradual but sudden).

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