My 2001 XJR heater is suddenly very slow to warm up - it takes 20-30 minutes for the interior to come up to temp on a cold day. I suspected the auxiliary pump, however it powers up fine when supplied 12 volts. I discovered I have no power to the pump with the ignition on/engine running. Wondering if the car has to be up to temp before this circuit is powered, or should I be seeing 12 volts here on cold start? Fuse and relay are fine and no HVAC system codes. Any ideas appreciated.

 

When was the last time you flushed your system? The car is 20 yrs old, the heater core may have buildup in it? When did you last change your thermostat,...is the water pump original...if so the replacements have metal vanes because the OEM had crappy plastic ones and would break. So if water isn't flowing, neither is the heat.

 

I'd recommend downloading the x308 workshop manual, think you can get it from jagrepair.com, or the forums large files section (Jaguar Forums File Download Area, Folder Index - Jaguar Forums - Jaguar Enthusiasts Forum)

From the shop manual:

 

Thanks for confirming the pump doesn't run on cold start - I'll warm the beast up and see if the pump circuit powers up. Water pump and thermostat were replaced along with timing chains and tensioners less than 5000 miles ago, and the heater core and evaporator are also new.

 

There is no power to the pump after bringing the engine up to operating temp and calling for heat. From the wiring schematic it looks like the engine temp sensor feeds the air conditioning control module which then switches power to the water valve and pump. Can I conclude it's either the temp sensor or a bad control module? I see there's a control panel code 14 for water temp input malfunction - since I'm not getting this can I assume the sensor is ok? Is there an easy way to test the sensor? My wife has a '99 XJR so I can always swap control modules when she's not looking. Any thoughts appreciated.