Only getting minimal heat.
I have not observed the heater water pump (small black cylinder?) running, even when fully warmed up.
I don’t see voltage at its input.

Coolant temp needle never leaves full left (cold) position.

Shorting the single-blade temp sensor wire (at themostat housing) to ground causes needle to tick up, ~one tick/second.

I assume that the little pump does not run until a certain temp is reached?

Is the sensor the likely culprit, or could a thermostat problem keep heat from getting to the sensor, even when fully warmed up?

What’s that other sensor (2-pin) in about the same area, near the thermostat housing? Should I suspect it?

Thanks,
gbmtkj

 

I'm pretty sure the pump runs at all times but at very least it should run when the system is set to give heat.

Replace your thermostat and your temp gauge will come up to "N"

Cheers
DD

 

Check the voltage at the aux pump. Some people have found that the fuse is blown.

 

If you can check the upper and lower hoses feeding the Rad if the temp are the same then the thermostat is faulty..

 

Thanks to all for the suggestions.

Doug, the problem did turn out to be the thermostat.
After replacing it and driving about 3 minutes, the temp needle left 'C' for the first time, and marched right up to 'N'.

AND, the heater makes good heat now. I can't leave it on '80' anymore!

Thanks,
gbmtkj

 

Thanks for your feedback , those will be useful if one of our members tackle with same problem