I have been having this problem for about a year now. I know it follows back to the tps sensor. It comes and goes. Now lately, my battery its getting bad.

I mean sometimes it won't have enough juice to start the car. I do know, a low voltage from the battery can cause electronics in vehicles to go haywire. As i was Today, as my lights were on, a/c on full blast, and the stereo on, it happened again.

I would get the cart out of limp mode after multiple key cycles and start to drive. About two miles down the road, limping again.

Then i noticed the car acting as if three battery was low. There was no batt light on, just things like the info display were dim and flashing with the beat of the song i was listening too.

The car broke again just as i noticed the low voltage. So, got the car moving again, shut all the accessories off, except lights, and made it home. Got home, pulled out the handy multimeter, the battery, with the car off had 12.6 volts. Turned the car on, applying the alternator's charge, 13.89 volts.

If rev it up and get my 14.05 from the alternator. Its obvious three battery is bad to me. One thing i did notice, each cell in the battery is low on fluid by about an 1" to an 1 1/2".

My question, again, is it possible that a low battery voltage could be causing this malfunction? Also, would it be worth adding some distilled water to the battery?The battery is original. My jag its a '04. I know its time for a replacement.

 

By the way. I know 12.6 volts is a good reading. I don't think my battery is hold its load. Im planning on having it tested tomorrow.

 

You've worked through to the logical conclusion. An eight year old battery is on borrowed time.

Graham

 

Also, my faults are parking break, engine system, and dsc. I didnt mean abs.

 

Its definitely the cheapest fix. Ya think its possible? If so, them allot of people who are going through this same issue is getting ripped off.

 

My dash light up like Christmas tree with full list of fault at the screen and car off battery registered 11.9v. Car drives fine despite all the warning message and light on. Change out the battery and it's been problem free ever since electrical wise.

 

I have noticed that this only occurs when i have been driving alot during the day. I know the throttle has coolant running through it, what if there is not proper coolant flow and the throttle body is getting too hot? Being that i work on electronics in the marine corps, I do know that electronics go insane when they are overheated, especially resistive elements. Any thoughts?

 

There are no electronics modules in the throttle body so there is nothing to overheat. The usual problem with this symptom is a failed throttle position sensor in the throttle body. Sometimes, it can be a bad wiring harness, but the TPS sensor failure is common.

 

I know the problem is thr tps, and that is elrctronic in its own way on the throttle body. Its basically a variable potentiometer. I was just wondering if excessive heat could damage it. I have been looking testing and researching, and it does seem as if its the connector. Every time it messes up, i re-seat the connector and the pins in the connector. After that, it goes for quite sometime flawlessly. Sometimes, it doesn't help.

 

So, my tps problem just became worse. Faulting about 10 times per day. In conjunction with this, the condition of my battery has gotten much worse. I had the car put on diagnostics. Found tps to be fine. The battery was running on about 11% of its capability. Just turning the parking lights on would kill it on the load test. The 680cca battery was using 138 cca's. Learned more about modern cars. The electronics in modern cars need the cat battery to operate correctly, unlike older cars that would run fine with the alternator. The alternator has to help provide that load. So, i bought a new battery, installed it, and started the car. I then drove the car. I tried to get the car to fault, applying s much load to the battery/alternator as possible. No fault yet. On the wary to the part store, a 6 mile drive, the tps faulted 4 times. Post new battery installation, no problem at all. The car also seems to operate better, like better throttle response and another shifting. At the moment, i will not completely claim a new battery fixes these tps problems, but perhaps that sensor is extremely sensitive to low voltage from a battery. Perhaps thus $500-$1000+ throttle body "fix" is unnecessary. I will continue to post the results of thus possible extremely easy and inexpensive fix. Lets hope my fellow jag owners! Fingers crossed!. I will report in again tomorrow night. Cheers!

 

Battery took care of some of my issues, but not the TPS. So, as I am an electronics technician and very familiar with electronics, I decided to try a new approach. Confidently, I rewired the wiring harness to the throttle control. So far, no faults today. Now, the only reason I decided to take this approach is because about two years ago, when my TPS fault started happening, I found that the wiring harness to the throttle control motor(not the TPS) had degraded and fell apart literally. I did a quick road side repair and I went trouble free for about 8 months. After that time period passed and the car re-continued to fault again, I would re-seat the connector I made for that harness to the control. That always seemed to take care of the issue temporarily. That roadside repair I did back then required me to cut off the old harness, just two wires, going to the throttle control motor on the throttle body. I then took two new wires, using butt connectors, connected the new wires to the old wires that were sticking out of the condoit on the engine wiring harness. I used gold plated connectors to connect to the throttle body. Today, thinking, perhaps there is a resistance that the butt connectors or perhaps the wire I was using in which could be causing a problem with the drive by wire system, such as the throttle valve not opening where it should in accordance to how far in I am pressing in the gas peddal. That resistance could be lowering the voltage to the throttle just enough to conflict with the proper position of the valve and where the TPS is expecting the valve to be. So, using my shops electronics repair tools; solder, soldering iron, shrink wrap, and some Silver wire instead of copper, I constructed a new, and professional looking wiring harness for the throttle body. There is to be no crimped connections, I ensured. I soldered everything together including soldering my custom harness into the engine wiring harness. I connected the two wires. Started the car, and immediatly, the engine light which was stuck on due to my p0121 code (TPS fault, which usually extinguished after a few key cycles)disappeared, the idle seemed smoother, and the transmission also seemed to change gears a bit smoother. The car faulted 32 times, last night and this morning. After this modification attempt, I drove home, testing all ranges of my throttle. No proplems as of yet. I will keep posting for all who is interested in this problem. I eliminated the problem to be a battery issue. Now, new hypothesis. Perhaps a degraded connection to the throttle body drive connector. I will continue to test.

SIDE NOTE: I tested the wiring with a multimeter to check continuity, my old wiring set up had 1.8 ohms between the butt connector and the gold terminal that would be connected to the throttle.
I then check continuity of my new custom harness. .6 ohms of resistance. That is a difference. Wait and See.

 

So, I drove about 100 miles today, no problems. My fix is still being tested. I am giving it a month of driving before I call my problem fixed. I'm not insinuating that my TPS problem is identical to anyone else's problem, but it is possible. The way I made my hypothesis is this. When you press the gas pedal, the potentiometer on the pedal tells the ECU how much voltage to apply to the throttle control, which opens the throttle valve the required position. If the wiring to the throttle control motor (which controls the butterfly valve) has resistance on it, the valve will not open to where the ECU wants. The TPS senses that position and reports it's position to the ECU to ensure the throttle is open correctly. So, lets say as example, if I were to press the gas pedal to a position that would have the valve open 25%, and the valve actually opens to 20% throttle, the TPS (which is expecting 25%) is going to assume, through circuitry, that the throttle is bad and the TPS will fault. The TPS is the only monitored component of the throttle body, so a multitude of thing not just the sensor itself could fail, potentially failing the sensor. In a nutshell, I think that my sensor was getting a bad reading due to the valve not opening correctly due to poor wiring. Hopefully this makes some bit of sense to whoever reads this. This is alot to explain. I put a year into this thought process, but I was stuck thinking it was the bad battery. We shall see. Feel free to contest my thinking here, please.

 

Congratulations on your diagnostic and remedial work ! Very good posts on what you found out and fixed. IMHO auto wiring in engine compartments is never specified to a sufficient standard of robustness when one considers the hostile nature of the environment.

 

USMC, I regularly read your posts and it seems IMHO you pretty much know what you are doing or can figure it out. My question to you is, if you thought your problem may have been a battery problem, and part of it may still have been, why did you take so long to replace it?

On another note, in my years when working as a yacht delivery captain, (still do at times), the Downtown Docks in Beaufort was my favorate stop on the waterway. The surrounding park with its bars and places to eat made it alot of fun. My first mate kept straight the town in NC from SC which is spelled the same but prononced differently by saying the woman in SC were beautiful.

Keep up the good work and thank you for your service to our great country.

 

Interesting post - as Barry says I think lots of us were waiting for a quick new battery job!
If I may comment, PLEASE put some line breaks in your text.

There's a lot of detail in there and it's so much easier to read if it's like this

So, I drove about 100 miles today, no problems.
My fix is still being tested. I am giving it a month of driving before I call my problem fixed.

I'm not insinuating that my TPS problem is identical to anyone else's problem, but it is possible.

The way I made my hypothesis is this.
When you press the gas pedal, the potentiometer on the pedal tells the ECU how much voltage to apply to the throttle control, which opens the throttle valve the required position.

If the wiring to the throttle control motor (which controls the butterfly valve) has resistance on it, the valve will not open to where the ECU wants.

The TPS senses that position and reports it's position to the ECU to ensure the throttle is open correctly.
So, lets say as example, if I were to press the gas pedal to a position that would have the valve open 25%, and the valve actually opens to 20% throttle, the TPS (which is expecting 25%) is going to assume, through circuitry, that the throttle is bad and the TPS will fault.

etc. No criticism intended, just trying to be helpful.

 

I really have no excuse for not changing the battery out much earlier than I did. I think I was bust just researching and trying to develop my own fixes to other issue's I've had with my Jag. I should have bought it a long time ago, being that it is the cheapest and easiest troubleshooting step available.

 

I thank you both for the complementary posts. And also, thank you for the advise. I did realize that my posts are jumbled together, and difficult to read. I will definitely fix this flaw, for the benefit of my readers.

I thank you both for the support on my efforts to resolve this TPS issue. Hopefully wiring is the common link between my TPS fault and other jag owners' TPS fault. If so, this keeps anyone from spending loads of cash on an unnecessary repair.

I will continue to post results, which I will immediately after this post.

It is my pleasure and honor to serve my country. Thanks you for the support.

 

I drove the "devil cat" today, still no issues.

I also did want to state this. A while back, I posted on a thread where my headlamps where intermittently flashing. This was happening in AUTO or MANUAL. When this happened, I would just turn them off and the on, problem gone.

This problem also disappeared after the battery replacement!

Seems to be, which I was to ignorant (by definition) to acknowledge, these cars cannot handle a battery that is even the slightest bit bad.

My Jag is the first car I have owned in which it is so technologically advanced. I have had other modern cars, but they were not as intricate.
Although, my '02 Jeep Grand Cherokee Laredo is MUCH more problematic!

I have had vehicles where you can drive with no battery. The past facts where car only used the alternator to operate post starting is no more.

I learned, which was probably a late lesson, that today's cars with all their computers require a battery because the alternator cannot provide enough power under such a rigorous load.

Like I said in a previous post, I am giving the Jag a month to prove my TPS fix. Today is only day 2. Until then, if anyone wants to know the dimensions, electrical values, tolerances, and the small number of components I have used to "fix" my Jag, I will be glad to tell you.

Use my method at your own risk of coarse, my TPS fault may very well be a different problem than others.

I have great passion working on cars and maintaining them. I am young, I have not gone to school to do such work, but since I was about 10, I have been learning the in's and out's of mechanics. I can say I know a great deal about vehicles. I certainly still have much to learn.

Later today, I am going to take photos of this wiring job I did and post it. It is a clean look. Sticks out though since I used yellow heat shrink. I'll let the readers of this thread to be the judge of this. I think it looks kinda cool. The Jag dealership will hate it since it is not original by no means. LOL HA HA HA.

BTW, is this format of text much better? I'm still practicing.

 

The P0121 is a compatibility issue with the connectors to the TB, P1121 is a fault directly related to the TB and replacement or rebuild is necessary. As for the series of cods and faults yes they are often related to an older battery but can and will show up on a failing TB. I will provide a few links that might give you additional information related to the TB itself.

P0121 Link JagRepair.com - Jaguar Repair Information Resource
P1121 Link JagRepair.com - Jaguar Repair Information Resource

As for your problem and suggested repair you need to post all your codes and what you were doing when it took place. I should mention replacing the battery was a good choice.

 

BTW, is this format of text much better? I'm still practicing.

10/10 for readability, thanks.