Hey all! I'm cross-posting this here and Jaguarforum.com, as this is probably a fairly obscure topic.

When I bought this car, I requested a vehicle specification from Jaguar. The listing revealed that the car was fitted with an electric engine heater; "ENGINE BLOCK HEATER 230V". Looking at JEPC, it was most likely a 700W Temro heater that heats the engine coolant (no circulation though). Heaters of this type are very common in colder climates, just not on newer cars as they rarely have the intended mounting hole for it on the engine.

As there was no cable to connect the car to a mains socket (Temro cables for European 230V spec are discontinued), I never used the heater. However, last week I had it removed and replaced with a Defa system (similar, but 600W I think), with a Y-piece for an electric interior heater.

The mains socket at my parking spot provides electricity for 2 hours, on a timer. That's enough to raise the coolant temp (checked with OBD2 scanner) some 25-30 °C above ambient temperature.

Unfortunately, if the pre-heated car is started after it has been sitting for more than 8 hours, it throws code P0116:





During this week, I've tested this with various sitting periods, in chronological order:
7h: no error
14h: error
9h: error
8h12m: error
6h15m: no error

My theory is that after sitting for 8 hours of longer, when started the ECU compares coolant temperature with ambient/intake air temperature, and if there's too much of a difference, concludes that the coolant temperature sensor is faulty. I've read that some recent cars have a similar setup, and apparently it's even required by some recent emissions regulations.

This is all quite surprising, as an engine heater is available from the factory. One would think that a heater-equipped car would thus be configured, at the factory, to skip such a test. I tried searching for a similar issue but have found nothing.

Any ideas?

 

If you clear the code and then let it sit overnight WITHOUT the heater working does it throw the code in the morning.

 

Maybe the car is smart enough to realize that the coolant SHOULD be ambient after so long, and it wants to start in ...open loop? Closed loop? I can never remember, but anyway, the value indicated does not match value expected. That WOULD be a pickle.

Once you've started it and let it run for a minute or so, have you tried shutting everything down and restarting again?

 

1. Does the car really need a block heater given your winter ambient temps?

2. What happens if you don't use the heater with regards to the DTC P0116 being logged?

3. Have you had a chance to review the items suggested by the repair manual:

Low coolant level
ECT sensor sensing circuit intermittent
Engine thermostat failure
ECT sensor failure

 

I'll try a cold start outside; best to cover all bases. Still, ambient temperature now is barely a few degrees lower than last week before the heater install, and being cold-started after long nights I never got a code.

Yeah, I do believe it's a feature that's working as intended, just without accounting for the factory option of an engine heater. No idea whether there's a place for it in the CCF or something.

Good point on the state of the loop...I was thinking that maybe the car sets the state of the loop based on how long it has been sitting, and perhaps starting with a closed loop after 8 hours results in the warmed-up coolant not being distributed quickly enough.

I did try shutting down and restarting once, though I did not get out of the car & lock it, which I reckon properly shuts the computers down? Perhaps I'll try that, too.

1. Probably not right now at +0°C (32°F), but as it eventually drops down to -25°C (-13°F), I'd rather have one. My drive to work is about 8 miles, and while it includes some highway driving, it's nice to get a headstart on warming up the engine.

Had it not been a factory-fitted option that has been on this car for 10 years, I could give up on it, but knowing that it's supposed to work means there ought to be some hope.

2. Haven't tried a cold start (outside) this week, but while I'm at work the car sits in a +15°C (59°F) garage for over 8 hours. That at least has never produced a code.

3. Coolant was replaced when the heater was fitted, level looks ok. No idea on the others, as I'm not getting any codes if the car has been sitting for under 8 hours, whether preheated or not. I've been logging coolant temperature while driving, and it generally gets to around +75°C (167°F) on highways, or around +95°C (203°F) in slower driving, cooling down again if I go on a highway. Based on what I've read these figures are normal for an XK.

I'm not aware of any issues with the thermostat, though as the car has done 64k miles, I'll probably have it replaced on the next service.

 

Simplest answer is to set the heater timer so it comes on only an hour before you need it. That's what I did with my Cummins diesel and it only got plugged in when the high temp was going to be below freezing. The Jag has a low volume, high velocity cooling system and the heater will cause the fluid to circulate just from heating it. Pop the hood and feel the hoses for reference.

You're not really looking to use the block heater to warm it to operating temps, merely above freezing. Might even be able to get away with 30 minutes of preheat or have it heat up earlier in the night so the heat has radiated around the engine bay and cooled back off when you hop in. Lots of simple answers that should help avoid the CEL.