Re. 2007 XKR:

I got a DTC P0128 "Coolant Temp Below Thermostat Regulating Temp" following a coolant change, so I credited it to a stray air bubble or such. Then the MIL lit about every 6 months. Now about once a week. Mostly winter months, and after erasing it does not occur which indicates to me that this is a transient problem ... the most difficult to track down.

The other day my wife noticed the outside temperature displayed was 0°F just as the MIL lit up again. So now I am thinking that it may be a fault with the Intake Air Temperature sensor.

Has anyone else had experience with this?

(Before I get all the usual no-help responses that I see on these postings, no, I have not driven the 2 hours to the dealer to leave the car for a week. And I live in coastal SC where it has not been 0°F since the last ice age. If it is a known issue with a faulty IAT, I can change it myself. So, please, helpful responses only. Thanks.)

 

There is a software update available for the 0 degree reading (I'm assuming you are referring to the outside air temperature reading on the head unit display).

Your Malfunction Indicator Lamp could be affected by the same need for the software update. There is another thread in the forum associated with this and is a TSB if I am not mistaken.

Information borrowed from another post by ejjbee:

The 0 degree F reading could relate to this TSB.

TECHNICAL SERVICE BULLETIN
This reissue replaces all previous versions. Please destroy all previous versions. Only refer to the electronic version of this TSB in GTR.
This bulletin supersedes TSB JTB00065/2007 dated 04 October 2007, which should either be destroyed or clearly marked to show it is no longer valid (e.g. with a line across the page). Only refer to the electronic version of this TSB in GTR.
reissue
No.JTB00065v2/2007 06 November 2007
Circulate to: Service Manager Parts Manager Warranty Administrator Service Reception Technicians
' Jaguar
All rights reserved.

Subject/Concern: Infotainment Update Model:
The New XK VIN Range: B00001-B15397 Markets: All
Section: 415-00 Summary The significant issues seen by customers are as follows:
1. Following a battery reset or software download the navigation screen displays in kilometres when the instrument cluster displays in miles.
2. Ambient temperature reading of 0"F at 59"F.
3. Customer inadvertently enters the touch screen calibration mode.
4. The vehicle powers down after one hour when not in use.
This version has been issued due to a change in the Summary and Service Instruction.
Cause: Software issues. Suggested Customer Concern Code - C20
The three modules affected (Front Control/Display Interface Module (high level display front), Infotainment Control Module and Audio Front Control Module) must be updated together. Do not mix old and new software versions. If any of the modules are replaced, the other modules need to be updated.
Action: Should a customer express concern, re-configure the infotainment system. Follow the Service Instruction outlined below.

 

My suspicion is you have an intermittently sticking thermostat AND you need the software update mentioned aove. I believe the ambient air and engine control systems use different sensors.

 

Interesting how I find this just insulting enough to not want to help. I guess when you step up with a big chip on your shoulder, i'd rather walk away.

Good luck with your issues.

Vince

 

Ambient air temp and coolant temp are not related in anyway.

If you have a scanner that does codes, maybe it also does real time reads. And if it does real time readouts then look at the coolant temp the same time you get the fault code and see if the coolant temp is up to the temp the thermostat should bring the temp up to.

Like suggested above in another post.........could be a sticking thermostat, possibly or a bad connection at the coolant temp sensor.

 

I too live some distance from the nearest dealer; and it is more than just inconvenient to make a special trip to this dealer.

If your thermostat and system is operating properly your thermostat should begin to open about 190-193F and be fully open at about 203F. A good scanner, like a ScanGauge, will measure your coolant temp.

If your thermostat is stuck closed, you will overheat, but this does not seem to be your problem. One symptom of a stuck-open thermostat is a heater that does not blow warm enough air, but this is not always the case - only in extreme situations.

If you find your coolant temperatures are within the above range, then focus on the coolant temperature sensor itself. Look for loose connection or perhaps a dirty/bad ground.

 

Good responses, guys. You are right ... ambient air temp and IAT are different sensors, so must just be coincidental. I'll look for the obvious loose connections first, then thermostat and IAT.

Bill Unger
1969 E-type FHC, 1997 XK8 FHC, 2007 XKR FHC

 

I have the same problem on my 2003 XKR. can you describe where the coolant temp sensor is located?

 

Within inches of where the thermostat is. I think I know what the next question is going to be (humor).