With clients in the car on a 103 degree day in Las Vegas the Jaguar with 58k on the odo decided to have a parkbrake fault, DSC Fault, and Engine Fault! I think every light came on. The car would not go above a mile an hour. There are too many faults at one time it must be electrical. Has anyone else had the same problem? How much did it cost to fix? Btw after a few re starts everything was fine. SO embarrassing with clients in the car!

 

Weird - if only "rebooting" the Jag fixed every problem they experience.

 

That's a typical dead battery symptom, heat and batteries don't mix well.
I'd start there and get your codes checked at the same time.

 

New battery as of less than a year ago.. No codes or faults now but very concerned it is not gone for good... Read on another post with the same faults something about the throttle body? Why would the throttle body give a park brake and DSC fault? Also why did the car not go into limp home mode or restricted performance? It wouldnt go even with the pedal down. Shouldnt it have at least gone into restricted performance?

 

Was the battery OEM? Just because it's newer doesn't mean it's not the culprit.

 

+2 on the battery. Get a hygrometer from most any auto parts store and check each cell. Sounds like one or more may be weak.

 

+3 on a failing battery - just because the battery is a year old doesn't mean one or 2 cells are essentially shot, especially with constant Vegas heat - good luck!

 

Will definitely check the battery but would the battery really cause the car to not be able to accelerate or drive?

 

Yes.

 

Just had a simular fault over last few weeks

Car goes into restricted mode and displays engine fault,no dsc etc when driving whenweather is warm, turn ign off for five mins and will drive for a while before going back into restricted mode. If external temp is less than 16 degrees the car has no problems.

It seems to happen when decelerating/or when cruise control is cancelled.

Read codes yesterday and had P0121,Throttle position sensor

Had a look around at the info available and deduced that when taking foot off accelerator or cancelling cruise the throttle closes and the engine management goes into closed loop mode, bringing in the Egr etc.

Looking under the bonnet I noticed the throttle body was hunting slightly on idle,
With the age and mileage of the car I figured if this was normal then the point of contact in the throttle position sensor at idle would have greater wear than any other position and as temperature increase you could have an open circuit condition causing the ECM to flag a fault condition.

Not having a 5 point star bit I was unable to rotate the sensor so took second best and removed the air inlet to see the throttle butterfly and adjusted the butterfly stop position down by approx 1 mm in the open position (leaving the throttle effectively closed) .

This moved the idle position of the butterfly relative to the TPS.

Been driving around into stop go traffic and via country lanes and motorway to see if I can recreate the fault.

Fingers crossed but as of yet it has not re occurred even though I have recreated the driving enviouronment where in constantly occurred.

Will have a long drive Sunday or Monday 150+ miles so will update afterward.

so could be a no cost fix.

any experts out there able to clarify if my logic on this is correct? Or have I just been lucky today with the limp mode not kicking in.


Apologies for the long write up and waffling on


Kind regards

Jeff

 

The logic is a little off but the fix MAY work (wait and see).

Lifting your foot off gas does not close the throttle butterfly. The gas pedal is not connected to it

What happens is that the PCM sees the new pedal position (multiple sensors for safety) and chooses where to put the throttle via its motor. The PCM monitors the actual throttle position via its sensors. Again, multiple for safety. You can't have ONE with a dubious reading because that will throw codes. You can't realistically have BOTH that go bad in a way that doesn't throw codes.

Aha - but you DID have a code. The codes PDF is worth a read as it specifically mentions the causes.

You still could be lucky.

BTW, it's closed loop essentially all the time.

I've no idea why you posted in this thread but if a mod would like to split it....

 

If I take it into the shop today will any codes pull up? I have no warning lights as of now.... Jeff I was decelerating as well and I have seen some threads talking about the Throttle Body being the problem. Thanks for your input!

 

You might get codes, from several modules (except maybe not the PCM since most require 2 similar circumstances to flag). Probably U codes (network/comms) but maybe others. You'll need a jag-specific tool to read those modules.

Start by checking no damp or water in trunk (remove spare tire) - cheapest thing to check!

If it's the battery, the codes may hint at it. If it's not the battery you're going to have a tough and likely expensive time figuring it out I suspect.

 

Gavin: Was it raining out, or had it been raining the past few days? If so......throttle body.

 

Now you've got the lowdown on the S-Type fix, I hope the clients are easily placated.

That must have been a toe curling experience for you.

Graham

 

If it's engine bay water-related then you need to concentrate on connectors. Ignore mechanical stuff.

 

Just a quick update. On mine

Done just over 200 miles today all sorts of driving conditions and pushed the car into situations where the fault would occur.

No fault

Not suggesting it's the cure all for everyone but it might be worth looking at as a quick free for 4.2 engines with same throttle body and mileage(84,000 miles),maybe not adjusting the butterfly stop position but rotating the sensor anticlockwise a mil or two.

Still early days though will update if fault returns or I get around to replacing the sensor.

I should have really started my own thread sorry new to this sort of thing
Could one of the mods shuffle my posts around a bit or something unless it's ok to leave my posts here,

Regards

Jeff

 

I'd guess it was likely dry.

Day Jun 24

104°FHigh
Sunny

Chance of rain:0%Wind:S at 17 mph Humidity:10%UV Index:10 - Very HighSnowfall:0 in

 

"the" implies there's ONE but there are TWO. I said so before...

Please, no-one take this advice without being ready for disaster.

 

No sure about disaster

Looking at the circuit diagrams for the 4.2 stype which gavin is refering too.
The TP sensor has TP1 and TP2 in the same housing. The system uses a 5 v reference voltage supply and a comon ground for all the sensors related to the throttle control. This voltage is electronically regulated and also I would not expect a dodgy battery to throw a throttle sensor fault while the engine is running and the alternator producing between 13 and 14 volts depending on the condition of the battery. Although other circuits and sensors would be affected.

TP1 has a range of 0.6v to 4.3v output
TP2 has a range of 1.43v to 4.4v output

I am assuming these are cross referenced with each other by the ECU to ensure the Sensor
Is good.

The sensor is mounted in such a way it is adjustable to calibrate it to the throttle body. If this calibration is out but the cross referenced voltages match the ECU should identify the sensor as still being good and lowest reading on initialisation of the circuit as being closed throttle position. If not then it will believe the throttle is slightly open and either flag a fault or control the idle speed by fuelling.


Which ever way most defiantly not a disaster

( now the bodge which I have done the get past the TP problem I currently have could allow the engine to idle lean if overdone, which would bring along a whole new world of hurt to my wallet lol. )