No heat in MK4 and a P0102 code

midairmark

Veteran Member
Joined
Aug 18, 2008
Location
GA
TDI
2001 Jetta GLS
I am not getting any heat in my 01 MK4 jetta. The temp gauge will not make it up to the normal operating spot (190). Plus, I have little bits of foam blowing from the vents. I am seeing a P0102 code as well.

I am looking and I see the foam could be from the blend door? I see a fix for that on the side, but I don't think it is causing the code and the temp not to reach normal. Car is stock except manual nozzles (IQ-about 4), van aiken smart box (been on for years, along with nozzles), 6 speed conversion (also been years). This is the first time I have been having this issue.

Is the thermostat or a temp sensor bad?

Thanks,
Mark
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
The foam will cause the HVAC air flow to not be directed over the heater core, which will cause no cabin heat, but will have nothing to do with the engine itself not getting up to temp.

The CTS has two circuits, one goes to the cluster for the gauge, the other goes to the engine controller for engine management. Both can be monitored with an appropriate scan tool. It is common for the CTS to fail, one or both circuits. It is also common for a thermostat to get weak. Actually, they only really last a few years anyway, but their decline can be quite slow until the end.

In your case, I would go for a new CTS, thermostat, housing, and related o-rings and new G12 coolant top up, and see how that does for you first. Common, easy, and relatively inexpensive, and your car probably could benefit from it anyway. Then see how your cabin heat is.
 

midairmark

Veteran Member
Joined
Aug 18, 2008
Location
GA
TDI
2001 Jetta GLS
Thanks oil hammer, what does CTS stand for, Coolant Temp Sensor? Also, should I use the factory temperature (is it 192F?) thermostat or change it to another temperature?
 
Last edited:

flee

Veteran Member
Joined
Sep 19, 2011
Location
Chatsworth, CA
TDI
2002 Jetta GLS wagon
Thanks oil hammer, what does CTS stand for, Coolant Temp Sensor? Also, should I use the factory temperature (is it 192F?) thermostat or change it to another temperature?
The OEM thermostat is best. Beware parts store 'replacement' off-brands.
 
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