Jag X-Type false overheat
 

After months of creeping on the forum I signed up. I bought a 2005 jaguar x-type. Everything was fine until I took it to the mechanic who wanted to replace everything on the car. For the purpose of this post the only thing he did that might matter is pressure test the cooling system to find a leak, after which the car began overheating. I have replaced the thermostat housing and associated pipes, and also the temperature sensor.
when warm the ECT has aprx 320 ohms of resistance and I'm getting 5 volts on the wire from the ECM. Using a laser thermostat gun I get 170-190 degrees F on any hoses or manifolds. The 190 is on the inlet pipe that holds the ECT. When the car overheats a quick cycling of the ignition generally brings it back to normal. I'm currently trying to check for shorts in the 2 wire between the ECT and ECM. I have also tried to induce a false overheat signal with minimal success, I can get it to show too hot on the gauge put it doesn't happen instantly, its like a delayed reaction after I short something intentionally. I know this is a common enough problem I'm just not sure of my next step. I don't believe the car has ever actually overheated, the occurrence is random at best usually after 15 min of driving but sometimes its good for an hour or 2, any help is appreciated, thanks

Your CTS
https://www.partsgeek.com/gbproducts...RoCv6sQAvD_BwE

I replaced that already, didn't make a difference. I guess I could be wrong on terminology but in the post I refer to it as a ECT, (engine coolant temperature sensor)

And once again, SEARCH is a marvelous tool = And pay attention to the , "I've checked all of it" = weak battery cause

https://www.jaguarforums.com/forum/x...heating-62734/

https://www.jaguarforums.com/forum/x...e-crazy-96901/

https://www.jaguarforums.com/forum/x...alarms-153271/

and on, and on, and.......

https://www.jaguarforums.com/forum/x...eating-121017/

I've read all those, I certainly could have missed something but I have been pretty thorough with my reading. My battery readings have been around 12.64 V with the vehicle off and 15.20 V running. I believe its a wiring or electronic issue, I'm just trying to eliminate things in precise method to avoid throwing parts at it.

Battery too low if @ 12.6. These cars are AWFULLY picky about correct voltage. A good battery should be around 13.3-13.5. At running, 15.2 is low end of good and should only remain at that for one of the 3 time units (depending on several factors) that the ECU tells it to recharge the battery.

And if you say you read those links, you must have skimmed them because "Thermo" the guru has instructions on how to run tests on everything, thus not "throwing parts" @ the problem.

I guess I wouldn't have thought of those voltages as being low, most vehicles I'm accustomed to are 12-13V off and 14-15V running. So if I am in fact running a weak battery, once the vehicle is running and driving some electrical load would cause the voltage to drop below a certain level that causes the code and the appearance of overheating? Once the load is removed the voltage goes up and the temp gauge returns to normal. would this battery be weak enough to fail a load test? And just out of curiosity is there something about this particular circuit that causes it to react to a weak battery when everything else on the car appears normal?

WOW, read post #4 in first thread from a Jag Tech......

And that was years ago before members reported problems with below 13+ volts

[QUOTE]
What is the age and condition of the battery? These vehicles require correct voltage at all times, so if you check battery voltage prior to starting the vehicle after several hours, it should be at least 12.5 volts. Anything lower can cause problems.

If there is any doubt about the battery it is best to replace it as a failing or weak battery can cause random DTCs and the MIL to come on.


Here is that post, So in my case my voltage would be sufficient, and my codes are not random at all. they are very specific and consistent.

Here's a post in a battery expert forum =

Turn the motor off with no load (headlights, etc. all OFF) and read the battery voltage.
With the engine just shut off, the battery voltage should be 13.2 volts to 13.8 volts.

So you can keep arguing, looking for some other component, or follow the testing suggestions that Thermo has posted.

The alternative is just more rhetoric and frustration on your part as you say you have replaced the normal parts that can cause this (with the exception of a radiator flush). Good luck, I'm done.....

Do you have a link the that battery expert info? Id like to read it. I took the battery in and had it load tested it came back as good at 12.8V, its less then 2 yrs old so I expected it to pass. I have never heard of a vehicle that required a regular or running voltage as high as you are saying, why would jaguar be different then any other vehicle? and more importantly why would a potential low voltage only effect this one circuit? Im not trying to argue with you, I'm here to gain knowledge and thus far you really haven't answered any of my questions.

Said I was done, but here's Jaguar's post on charging system =


Vehicles With 2.0L, 2.5L or 3.0L Engines

The charging system consists of a 120 amp output generator and regulator assembly which generates current to supply the vehicle electrical system with electricity when the engine is running and maintain the battery in a charged condition.The generator is belt driven by the accessory drive belt.

When the engine is started, the generator begins to generate alternating current (AC) which is converted to direct current (DC) internally. The DC current and voltage is controlled by the voltage regulator, (located inside the generator), and then supplied to the battery through the main battery positive cable.

The generator is solidly mounted to the engine timing cover and is driven at 2.8 times the engine speed.Vehicles fitted with manual transmission have a one way clutch fitted to the drive pulley, which prevents torsional vibrations from the engine being transmitted to the generator.

The engine control module (ECM) can switch the voltage regulator between two voltages to optimize the charging of the battery.The low voltage regulator setting is 13.6 volts and the high voltage regulator setting is 15.3 volts, measured with the generator at 25°C (77°F) and charging at a rate of 5 amps. These values decrease with a rise in temperature or current flow.

The ECM determines the voltage setting of the voltage regulator. The high voltage setting is always selected by the ECM once the vehicle has started. The ECM determines the period of time that the high voltage setting is selected for.There are three different time periods selected by the ECM which is dependent upon the vehicle conditions when the vehicle is started:

The longest time period is selected if the ECM determines that the vehicle has been 'soaking' for sufficient time to allow the engine coolant temperature (ECT) and the intake air temperature (IAT) to fall within 3°C (37°F) of each other.

The intermediate time period is selected when the ECT and the IAT are below 5°C (41°F).

The shortest time period is the default time and is used to provide a short period of boost charge.

At the end of these time periods the voltage is always set to the low voltage setting to prevent the battery from being overcharged.The time periods are variable depending upon the temperature and the battery voltage.

The target voltage of the battery varies between 14 volts and 15 volts depending upon the ambient temperature and the vehicle operating conditions. Once this target voltage has been achieved, providing the vehicle has been operating for at least the shortest time period, the ECM will reduce the voltage regulator to the minimum setting of 13.6 volts. Now I'm completely done....

Thanks you for that, it is knowledge I didn't have about the car. The way I read it is that while running the voltage should be between 13.6-15.3 volts. I fall within that range at 15.2 V. So as long as my generator and voltage regular are operating correctly I should never have a low voltage problem, the only time the voltage would be below 13 V is at initial start up. The vehicle false over heats mid trip when the battery should be good and charged. Now if the voltage regulator was bad on the low setting when the ECM switched to it, it could cause a problem, but why a false temperature signal and not something else? The ECM only sends 5V to the ECT but if it fell below that it wouldn't change the resistance of the ECT only the V to A ratio, I am under the impression that the ECM reads the resistance from the ECT to determine temperature, but if it read V or A it could potentially give a false read and then return to normal when the voltage regulator switches back to the high setting. But once again why this circuit only? If I had bad voltage due to a battery or something else shouldn't it show somewhere else too?

Try replacing the CTS again, you may have fitted a dodgy one.

I thought that too, I resistance tested the new one and the old one and they both tested good. Oddly enough after I moved the wires between the ECT and ECM around during my testing I have made three different trips without it acting up, which seems to support my original idea of a short. Its too early to dismiss another cause but Im thinking my next steps would be replacing those 2 wires and probably the CTS once more just to be safe. I will keep driving it in the mean time to see what it does.

Thermo's quote in one of the above threads =

"gunslinger, not to ask the silly question, but did someone hand over hand the wiring backwards towards the ECU and check to make sure that the wiring was damaged? It can also be something as simple as the plug to the sensor has some corrosion on the terminals and that is leading to a high resistance connection. The increased resistance would make the computer think that the car is running hotter than it really is. If you need to know how to check the wiring, let me know."

amazing how READING stuff gives you guidance......

I appreciate the sarcasm I continually get from your responses, In the original post I suspected a short, you would know this assuming you read it. I was asking for other suggestions because I couldnt find a definitive problem. I still have not found any obvious signs of a short or corrosion it just seems to be the best explanation at this time. I have and continue to read all posts regarding this issue, this process started long before I joined the forum.

still overheating?
 

Did I read that you already replaced the thermostat? Did you find any wiring issues?

That's correct thermostat, housing, and hoses are all new. I replaced the connector on the temp sensor but it didn't change anything. I suspect the wire is shorted on top of the engine somewhere. I intend to replace the entire length of it when time allows. For the last 10,000 miles I've just been driving with my scan tool plugged in and when the check engine light comes on I have about 2 min to clear it before the temp gauge moves, if I miss the window and the gauge pegs out it returns to normal within a minute of clearing the code.