Temp gauge problems

[franke08]

Sorry for the bad english, Im from Germany. I have a problem with my 2006 H2. Since i have built in a WEBASTO engine-and inside-heating system, wich is also connected with the fan for inside heating, the temp. gauge is not working correctly. Every time i have used the heating system the temp gauge only works for 5 to 10 minutes and then it goes back to zero,even the Webasto heater is already off.. If i dont use the Webasto heater everything is normal. After two days without the Webasto heater, the gauge is working good. If i use it again, then the gauge is not working after 10 minutes, even the Heater is shut down befor I start the engine. When I erase the failor code in the bordcomputer, just in this second the temp gauge is working normaly. Everything is good when I dont use the Webasto Heater. But this Heater ist powered by fuel and only conected with 12 V power and the fan for inside heating by using a relay. When the Webasto system is on, then the wire wich comes from the climatecomputer to the fan is hanging in the air, there is no connection between any module and the Webasto system. When the Heater is off, then the relay connects the climatecomputer with the fan and than is there no connection with the Webasto heater. GM Germany dont know why it is so, and they can not help me.
Does anybody have an idea?
Thanks for reading and for your help

[pdsq99f4]

What is a wabasto heater and what is the code that you keep clearing?

[Biskxp]

http://www.webasto.co.uk/am/en/am_automobile_3177.html

Engine and Cab Pre-heaters.

[HUMTECH]

You are likely setting a p0116 trouble code. The pcm uses ect temp and iat temp and after about 10 minutes of run time compares the two, if the ect temp is too high as per the pcm's calculations it set dtc p0116 and the temp gauge will default to cold and the ses light will come on. Very common with an aftermarket coolant heater as it raises the cold start coolant temp much higher than the stock block heater. Try just using the heater approx 1 hour prior to starting the engine so the coolant temp does not get too high

[franke08]

Originally Posted by HUMTECH

You are likely setting a p0116 trouble code. The pcm uses ect temp and iat temp and after about 10 minutes of run time compares the two, if the ect temp is too high as per the pcm's calculations it set dtc p0116 and the temp gauge will default to cold and the ses light will come on. Very common with an aftermarket coolant heater as it raises the cold start coolant temp much higher than the stock block heater. Try just using the heater approx 1 hour prior to starting the engine so the coolant temp does not get too high

Thank you, now I understand what happens. But when its cold outside I would like to have a warm car. When I start the heater to early before startin engine, its already cold inside. Is there any other way to protect setting the trouble code?
By the way, you are the best expert i ever met, GM in Germany did not know anything about comparing the two temps. Really great!! Thank you

[HUMTECH]

No way that i know of to make this work. It may be possible through custom programming but not sure. One thing you could do is buy an inexpensive code reader and leave it plugged into the data link connector, when the code sets just clear it.

[franke08]

Ok, if there is no other way I have to live with this problem. But there is one thing that I can not understand: When I shut down the engine after driving and I come back 1h later for driving again, the ect is also high, but no error is coming. Is there also a comparing of ect and ait, or "knows" the pcm that the engine was running one hour before? Maybe I could start the engine, then shut down and start again. Aftermarket preheaters are very common in europa, but it seems that I am the only one with this problem. Its also cold in Canada, do you also use preheater-systems?

[HUMTECH]

The pcm has an internal clock that knows how much time has elapsed since it was shut down and calculates accordingly. Yes its cold here but i have not seen or had any experience with preheaters other than in diesels. Most here just use a remote start and warm it up that way.