So I've been having seemingly random issues for a while now. Maybe a year. 2002 XJR, 140k miles.

Car was doing fine, then started throwing error codes. Cruise quit working early on. Sometimes the cruise light will illuminate, others it won't. Next, it started throwing "engine fail safe mode" pretty much every day (daily driver). With an occasional "restricted performance" thrown in for good measure. Usually the restricted performance happens at startup and it feels like it's running on 6-7 cylinders. It usually disappears within a half mole or so of driving. Occasionally it will appear while driving and you can feel the stumble, then clear up again 30 seconds later.

Most recently it started throwing "check rear lights". Only tail and front marker lights weren't working. And the passenger brake light. Every other light is ok. Cruise is still out 98 percent of the time. I spent several hours troubleshooting the marker lights/one brake light today. All fuses and relays good. Suddenly, all the tail and marker lights started working (they've been out all week), but the brake light does not still. And, all the warnings are gone on the dash. First time in months and months without a yellow or red light on the dash with a message. I drove 1.8 miles to get gas. Sitting at a light, car starts shaking, restricted performance, scrolls to engine fail safe, and then check rear lights. WTF? Then, not 15 seconds later all warning disappear and car runs smooth. Acts fine all the way home.

Oh, one more thing, last year the car would stall when I took a hard left. Not just as all, but a hard reset, like you disconnected the battery. It has quit doing that now, too.

And the transmission will randomly throw "high temperature gearbox" faults also. Mostly on first cold start of the day. I can usually clear it by stopping and restarting half a dozen times or so.

I was thinking a driver in a module (BPM for marker lights) was bad, but I'm doubting that since they are working again. Even with no errors on the dash on the way home, cruise did not work, even though the light was on.

So, any idea what is going on, or what to look for with the plethora of (seemingly random) faults I am experiencing? It's getting pretty tiresome wondering if I'm going to be able to get home for work on a daily basis.

Thanks for your thoughts,

Mike

 

Mike
You should see if DTC codes might have been triggered. You can purchase a code reader or have auto parts store do the DTC code scan for you.

If there are any DTC codes, then post them here on the forum and we will be able to help point you in the right direction. Let us know either way, someone on the forum will come up with some advice.

Jim Lombardi

 

That whole mess could be the result of a weak battery. When you get the codes checked, ask them to load test the battery.

 

Jim, only current code is P0356, ignition fault (hence running on 6-7 cylinders like I was describing). Usually a bad coilpack(s) shows up when hot, not at cold start though.

Pending codes are P0356 again and P1111 IAT intermittent high voltage.

That's it.

Thanks,

Mike

 

I've tried running the car off a brand new battery with the same issues (not with this new round of errors though). The battery was for one of my other vehicles though, so is not in the car at this time. I could get the battery tested for good measure though I suppose.

Thanks for the thought.

 

That P1111 is to be expected, says internal emission checks completed. If you disconnect the battery it will show P1000 until checks are completed.

 

I'd run through the electrical system. Check out the electrical link in my signature, and pay special attention to the battery cables in the trunk. Flex them by hand while making measurements. These cars are very sensitive to voltages.

 

P1111 is not to do with IAT. It's a (good) status code.

 

Guess my code scanner has a poor database then, as that's what it said the code was. I didn't check it against online info.

Guess I'll see the car does on they way to work this morning.

Mike

 

I get the "check rear lights" when my battery gets low. I do a lot of short trips and sometimes the car will sit over the weekend. After a couple of hours on the trickle charger all is well. I would recommend cleaning all the ground and power points. They seem to cause a lot of mysterious problems also.

 

Car started fine this AM, drove 15.5 miles with no errors, then engine failsafe and check rear lights warning came on while cruising at 50 mph out of the blue. Leaving work, no codes, drove about 1.5 miles, codes show up. Stopped to get kids on the way home, started with no errors, then about 400 yards later, codes.

I drive ~35 miles each day to and from work, so the battery should have plenty of charge time. I will get the battery checked; hopefully I can find time this week. Job + wife + 3 small kids = not a lot of time to do things away from the house.

Mike

 

All P1xxx codes are (by law) make/model&year specific so an OBD tool ought to describe them appropriately. Sadly, many tools are close to junk in that regard.

 

Quit screwing around and buy a new battery.

Did you swap a new battery in? I don't know what you mean by running car off new battery?

You have all the symptoms.
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.
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These Jaguar electronics are sensitive to having the correct voltage that only can be provided by having the correct battery that is specified for it.

If you have a weak battery or the incorrect battery, then you will continue to have electrical issues.

We purchased a new battery in 11/2009 - maxx 49n at our local Walmart store. It is still going strong with no issues.

Jim Lombardi

 

Brand new battery, disconnect Jag battery cables, place other battery in trunk, use jumper cables to run Jag off new battery. Jag was running off new battery.

Mike

 

I doubt the battery is the whole issue, BUT when you are runnning on a battery with long leads (the jumper cables), you have potential for both voltage loss and voltage fluctuations in the electrical system due to impedance between the voltage sink (the battery) and the noise generators and load (the car), so you have not actually run a good test. What apparently happens is that deteriorating capacitors in the various control modules degrade with time and temperature and therefore make the modules more susceptible to voltage spikes and variations. A good battery with low impedance connections mitigates these spikes.

At least some of your related issues could be due to a bad brake switch. Also, check the underhood "false bulkhead" connections, the engine ground strap, and the battery connectors, including the battery ground strap. Then look for loose connections and corrosion on the several hundred (it seems) ground and power connections on the car.

 

Thanks, I have checked the false bulkhead, the engine ground strap, and battery cable connections previously. On the whole, he wiring and grounds appear to be in good condition, with no signs of loose or damaged wires, or corrosion. Do you have a suggestion on areas to focus on inspecting the grounds more closely?

Aside from the brake switch being “bad” and outright not working, do you have a theory for how it could affect the other modules on the car? Viewing the schematic, it appears the brake switch is simply that, a “normal” switch in a standard 12V circuit ,at least the portion leading to the relay driving the HMSL, which seems to be working fine.

Thanks,

Mike

 

There are two brake switch circuits. Thanks to red1bw for this snippet:
"The brake switch is referred to as the BPP switch, Brake Pedal Position switch. This makes it much easier to global search. It appears to have 2 switches within the BPP: one for the brake lights directly, and one to tell the cars CPU if the brake is pressed (and probably how much it is pressed as it does have 4 wires coming from it). The CPU can then disable cruise control, disengage the lock up converter, probably recognize emergency stopping.

I expect that you have several possibly related problems. Of course, you might have a bad body processor. If so, it is a pain in the *** since the mileage and security features are there.

 

I didn’t realize there were multiple circuits in the brake switch. That’s a definite possible to be one of my issues at least, I’ll look into it.

Thanks,

Mike

 

The switch can be checked while in the car, but it's not easy to access. i have done this on the XK8, and the switch is the same.

Locate the plug, stuffed in the insulation above the brake pedal, and disconnect. The innermost and outermost pins are pairs. Check continuity with a meter with the pedal at rest and depressed and you should see the the switches open and close.