I am getting a code P0116 and P0128 which seems to indicate thermostat or sensor problems. Sometimes the check engine light is on and sometimes when I am on the highway the car will go into decreased performance mode and the engine temp gauge immediately goes to the top even though the car is NOT running hot. The car continues to run fine at highway speeds and only lacks performance when I slow way down. I can get off the highway, stop, shut the car off, wait 20-30 seconds and restart the car with no problem and no longer in limp mode but the check engine light may remain on - temperature gauge only goes to 1/4 or 1/3 up after starting.

Also, is installing the thermostat (dealer says it is the newer kind according to my serial # and not the normal drop in kind) something I can wrench myself?

Thanks for any insightor help!

 

year would help when youre asking for help. p0128 is temp below threashold(sticking partially or fully open) I dont remember p0116 of the top of my head

 

The year is a 2005!

 

change the thermostat, its got a rubber seal inside around the thermostat disc that tears and causes this code. replace the thermostat and clear codes, see if the p0116 comes back but it probobly wont. I think that for a sensor malfunction, but the issue is more probobly set because the ecu didnt believe what it was seeing for temp cause of the t stat fault and set that code. yes you can do it yourself, its a couple clamps, 3 torx bolts and you have to assemble the t stat yourself. take out the air bleed on the coolant reservoir without the engine running to get air out

 

What do you mean by "take out the air bleed" on the coolant reservoir, and how does this get the air out?

 

http://www.amazon.com/Neiko-Socket-1...1305724&sr=8-1

Will this Torx bit set work for this?

 

yes it will. all you need is a t25, a ratchet, and some pliers and you'll be set

 

Too late. I am paying a jag dealership $400 to do it. Yikes!

 

there is a cross slotted plug in the top of the coolant reservoir by the hose pipe that always cracks and leaks. unscrew it with the engine off as you refill the cooling system. This is the high point and lets air out from the system so you dont air lock it. Fill till you quit seeing bubbles. I like to squeeze the upper radiator hose to speed it up

 

A Ford V8 in another vehicle I have has a problem with the cooling system, that many mechanics could not diagnose, and it may be the same as yours.

The temp gauge would read cold for an abnormally long amount of time, then would shoot up to max temp, and the engine would go into limp mode.

After mechanics wasting $1000 replacing the water pump, thermo, belt, and having the cooling system flushed, I did my own research.

I found when there is a leak between the exhaust and the cooling system (leaky head gasket or cracked head), it pressurizes the radiator side of the system and holds the thermo closed. The temp probe is on the other side of the thermo, which is why it reads cold so long.

Then the water is continuing circulating in the block long after the thermo should have opened, and when it boils over it forces the thermo open and is why the temp gauge shoots to max hot.

Also you can ensure the temp gauge is working properly by putting your hand on the upper radiator hose after you've driven a few miles, it will be stone cold. Then when the thermo is forced open by lava hot water in the block, the upper radiator hose will be smokin hot.

You can verify if you have a leak between your exhaust and coolant systems, by a test large repair shops can perform. They take a coolant sample in a tube, and it will change to a certain color if there is exhaust residue in it.

We don't repair major engine problems anymore, so the shop will quote $6500 to $15,000 to replace your motor.

There is a way to jerry rig a vehicle in this condition to be almost fully operable. Loosen the coolant overflow cap until it is almost off, and tape it in place with duct tape to keep it from fully coming off. This will unpressurize the cooling system, and allow the thermo to open at almost the proper temp, and keep the temp from shooting to max and the engine entering the limp mode.

It will work unless you are in a desert environment or towing, because water will boil over at a much lower temp. In any case it is only a temporary bandaid.

 

What year is your XJ?

We just had the same code (P0128) and the dealership fixed (replaced thermostat) under warranty... John, our service manager/writer told me there was a service bulletin out for this... We have a 2006 XJ8 with Select Warranty and bought the car Jaguar Certified... not sure if a service bulletin is for all or just warranty but thought I'd let you know.

I also bought a highter end code reader since purchasing this last auto... I like to be "armed with information"

 

2006, but I don't have a warranty on it. I like to live dangerously!

By the way, the CEL has not come back.

 

That is "livin' Dangerous"... lol Our CEL came on about two months after bringing the car home which is when I bought my scanner... I didn't want to make the two hour drive back to Hartford to get it diagnosed. I erased the code and it stayed away for about 6 months before reappearing.
Also, when I had a CEL warning on our last XJ (1995 XJ6 without warranty), I found a mouse nest in the air box, cleaned it out, bought a new filter and the light stayed on... Called the local dealership and was quoted something like $120.00 for a diagnostic even though I was sure of the problem it was going to cost the same to erase the code (at the dealership)... this is when I thought about taking my $120.00 and added another $100.00 investment and buying a good scanner... Well, it took buying another Jag to pull the trigger on the scanner...now I'm truly dangerous... lol

Good luck...

 

What kind of scanner do you have now?

 

I purchased an Actron CP9175... It's a good mid-range scanner that you can plug into your computer at home... not the best one out there and certainly not the worst. Given my novice mechanical (on newer cars...especially Jags) abilities anything more advanced would be dangerous. I bought this one because I can erase codes rather than take the car in after I fixed whatever problem and to also tell my service manager what code is displayed. I can research the problem and have some sort of intelligent conversation with my service manager also rather than simply... my engine light is on.

 

I scanned through most of this thread about thermostats looking for information about after-market thermostats. Has anyone had any experience with them and any particular brands that are good or bad. Thanks for your replies.
Spillwaybob (Bob)

 

I am having a similar issue with the P0128 code- any help would be appreciated. My '06 XJ8 w/63k was taking a long time to warm up and set a CEL with the P0128 code. I replaced the thermostat which improved warm up time a little but within 24 hrs has set another P0128 code. The car blows warm air within 2 min of starting so I think the temp gauge reading may be wrong...

 

Be carefull on this code. As these cars and plastic are getting older, the inner plastic piece that holds the thermostat in place wil break apart inside after youve installed the t stat and give the code again. Its happened to me. So for the most part ive started to just replace the whole housing which includes a new thermostat. These housing leak when they crack so youre really taking care off 2 issues at the same time.
Aftermarket parts....hmmm,, sometimes you get what you pay for. I just replaced a leaking water pump on my daughters xtype that was aftermarket and the previous owner had a aftermarket unit installed a yr and a half earlier

 

Brutal: Which housing do I need- just the part that houses the thermostat or the one with 4+ outlets and the temp sensor?

 

I'm only getting the PO116 code. Does that mean I just have to replace the sensor and I should be fine?