2000 XJ8, 64K miles. Starting 8-2012, about 1x/wk lose CC, then CC light goes out & finally get FSEM, amber not red. If I cycle ignition usually everything OK again.

Many threads on this but I’ve read when it is linked to CC, it is often the brake pedal switch/sensor that needs replacement. LNB 6420BB. Jaguar has a TSB on this amended 4-2002 206-07. But my last 6 of VIN is after # F05566, mine is F1xxxx.

I may want to replace this & see if problem solved. I can buy a new one from Jaguar for $83. I read that you d/c battery cable & remove 2 small bolts & remove wiring harness & then swap the switch. Seems fairly easy... if I can find the thing! Would love to see photos of this switch in place. Did see pix of switch not in place post #8 here:
https://www.jaguarforums.com/forum/x...n-light-76654/



I can’t see mine! I was looking in my driver side footwell near the brake pedal with a flashlight & mirror. I see a white plastic wire connector attached to the upper brake pedal arm but, don’t think that is it.


I replace batteries ~ each 5 yrs. Last, 5-15-2010, I again used Interstate MTP-93 (850 CCA, 85 month) & my last battery had not failed, rather tested marginal but, they let me prorate it anyway. I really doubt it is a battery problem.



OBD-2 code shows only the All good (P1111). I used Innova 3130.

No noticeable change in drivability except cruise control not working. No loss of power or rough running or jerking as when Ignition coils have failed in the past.

Read about Throttle Body causing this too. I think mine has been cleaned, not sure how to do it, just spray stuff in there? I’ve had it exposed when I changed Ignition coils a few years ago. Looked clean to me, <GRIN> I had my restricter in engine part load breather cleaned @ 17K & again @ 44.6K & Jaguar says not necessary to do it unless black smoke.

I removed the engine protective cover (one bolt) over the brake master cylinder & checked the vacuum hoses & everything seems connected OK.

ABS module rebuilt 1-2012 for different problem. MAF cleaned 2008 & replaced 12-2009.

 

Steve,
You don't see the brake fault P1571 code with an OBD reader.
You're symptoms do seem to point to the dreaded switch though.
If it was a TB problem you'd get readable codes.
Here's one of many replacement threads
https://www.jaguarforums.com/forum/x...allenge-83605/

 

Thanks, Steve!
Glad to hear that no code probably means no TB issues.

I read that thread & OMG! Much harder than I thought to change the switch. Seems like you need special smaller tool plus 2nd (small) person & still not easy.

I think the switch is much higher up than I was looking. I think the bolts go into the firewall which can be accessed from the engine compartment under the brake master cylinder. But only the holes, once you have removed both bolts. So must remove the bolts, blind, by feel & then can thread bamboo & line through the holes from up top so a 2nd person --cramped into the footwell --can attach the new switch to the line & then you pull up & hold in place as they replace the bolts. Sounds like a nightmare. I really need to see what I’m doing. Maybe I’ll get a quote from Jaguar for cost to replace switch? They would also have a full diagnostic computer that can verify if, in fact, it is the switch that is bad. I will bet it will be $250+ rather than $80 if I DIY.

 

OMFG, this one sounds like a nightmare....just experienced the same symptoms and am probably looking at replacing the brake light switch.

I can't believe it has anything to do with the cruise control or the "engine fault" light I'm getting on the dash, though. And do you still have brake lights functioning even though the switch is bad? I never checked.....

 

It has not done the FSEM since 11-1-12 for some strange reason.

I did have the CC fail for a few minutes & then back on again 2-3 x since then.

I do not know if the brake lights work or not while it is in FSEM. I think they do. I tried to see the glow from the high brake light in the rear window. Hard to tell in daylight.

I bought a battery tester:

Equus 3721 Battery and Charging System Monitor


It arrived 11-15-12, it read my 1.5 yr old battery as 12.2V. which is only 50% charged! It read my charging system as OK. I went to an Interstate Battery dealer the next day & they tested my battery as “marginal” & did not test my charging system but replaced the battery at N/C since w/in 30 months. I tested again & the new one reads as 12.2V as well! Charging system still normal. Not sure if the battery tester is accurate or not. It plugs into Cigarette lighter outlet. Ran the car 65-70 mph for 20 minutes Saturday hoping to top off the charge in the battery in case sitting at the store allowed the charge to go down some. It tested @ 12.3V. BTW, car starts just fine. Testing the charging system in park revving engine to 2500 RPM tester reads 14.1-14.2V which is in the normal, good range as per Innova/Equus instructions. Don’t know if Jaguar has different specs for alternator output @ 2500 RPM.

I will wait & see if it happens again. At least this should eliminate the battery as a possible cause of the FSEM/CC issue. I may try to see if I can use my new tester on a couple other cars to see if I also get only 12.2V which wold suggest the tester reads too low.

 

How are you using the tester? I notice it plugs into the cigarette lighter socket. This is only live when the ignition is switched on, which will easily draw enough current from the battery to depress it's voltage as various vehicle systems will then be energised & draw current from the battery.

The tester is measuring the voltage at the cigarette lighter socket with the ignition switched on, which will give a lower reading than a conventional multimeter connected directly to the battery itself with the ignition switched off & no electrical loads depressing the battery voltage.

The battery is in the boot of the vehicle & the tester is measuring the voltage at the front of the vehicle from wires that have current flowing through them, which will incur voltage losses & give an artificially low reading when the ignition is switched on.

Just a thought...

 

Yes, I am plugging it in to cig lighter & then I turn key to on, (do not start engine) I turn fan & lights off, then turn lights on 10 sec to remove any surface charge then off again. I realize this may not be accurate but, the reviews on Amazon & elsewhere are very good including from some engineer who tested it compared to directly measuring with a multimeter direct at the battery. I think your concerns are also valid for other cars with battery in the front engine compartment. Maybe Jags draw more current from battery even if we think “everything “ is off vs. other cars?

To test charging system with car warmed up, I put in park & turn lights, radio, fan etc. off & rev engine to 2500 RPM. I read 14.12 V today. instructions say ck your manufacturer specs but typically 13.3-14.4 is Good, 13.1 & 15.0 are marginal, 12.6 & 16.0 bad. They have a chart.

I’m curious to see what happens with other cars. Even if it shows 12.6 for battery ck on other cars, it does not mean that it is reading my jag correctly.

Maybe I can borrow a multimeter & check. That would be the best test.
May turn out to be too good to be true to simply plug a $16 small device in the cig lighter & test away w/o any helpers or opening hood or trunk.

 

The device is not at fault-it's simply measuring the voltage it sees at the point of measurement, in this case the cigarette lighter socket.

I know what you're saying about removing the surface charge by turning the lights on for 10 seconds & then off again, but the problem is that the cigarette lighter socket on the Jag only become live when the ignition is switched on-and when the ignition is switched on, without engine cranking, a large electrical load is drawn from the batter anyway by all the various electrical systems on the Jag.

So as well as removing the surface charge, turning on the lights together with all the ignition-switched electrical loads is actually going much further than just removing the battery surface charge. It also depresses the battery voltage below the level you'd see if you'd just removed the surface charge.

So there's nothing wrong with your voltage tester & nothing wrong with the battery either-it's the test measurement method that's giving you these particular results.

Also, the cigarette lighter may well be taking it's supply from a point that also supplies other electrical loads when the ignition is on-so with a few amps flowing in the wires from the boot to the front of the car, you can easily be losing 0.1 or 0.2v in the cables as well.

Most charging systems run the battery voltage at around 14v although it's usually temperature-compensated to a small degree. In cold weather the battery will require a slightly higher charging voltage above 14v-typically around 14.1-14.4v. In very hot weather the charging voltage is reduced to below 14v, usually around 13.5-13.8v.

The only way to truly measure accurately the battery voltage is to completely disconnect it from the car, leave it overnight for the surface charge to dissipate, and then measure the battery voltage directly the next day.

There's nothing wrong with the testers that plug into the cigarette lighter socket, but they'll only tell you the voltage at the cigarette lighter socket. So to interpret the results correctly, you need to know the wiring layout of the car & the cable resistance, and the current draw with the ignition switched on-so you can know the voltage drop lost in the cables from the rear to the front of the car.

 

Hi
Here is a JPEG showing the Brake Switch attached to the Brake Pedal on XJ (X308) I copied from a TSB for the Brake Switch (206-07AM3) - It is also in the TSB sticky thread.



Jim Lombardi

 

I have a difficult time believing the brake switch is enough to mess with the cruise control, but if so it is not as difficult to replace as some people make it out to be. I was able to get under the dash and reach it. Question is, do I waste $75 bucks on a part that may not cure the problem with the cc.

 

I had the same problem w/ my 98 when I bought it a few years ago. When I engaged the cruise control, I would get the Failsafe mode warning. Restarting the car would clear the warning until activating CC again. It generated a code indicating a fault w/ the MAF sensor.

The actual cause of the problem had nothing to do w/ the MAF sensor, however. After a LOT of work on the part of the dealer, the fault was two vacuum valves that controlled some aspect of CC operation. TO get you the part numbers I will need to get my maintenance file. I think I posted this issue on this forum or over at jag-lovers.

 

Red October,

All your points are good. I still wanted to run more tests to know if this device is useable for me & my Jag. When I 1st read about testing the battery @ the cig socket it didn’t seem plausible. Then I thought that maybe there is some compensation built into the device due to the distance from the actual battery. But, then that would differ for each car. So, the drop off in voltage must be trivial or else all those reviews (Amazon & other web sites) would not be so positive especially from the guy who said he was an electrical engineer & compared with a multimeter @ the battery & this device was extremely accurate. So, I took a chance. Instructions state:
1) plug in
2) Turn ignition “on” Do not start car
3) Turn lights on 10 sec to remove surface charge & then turn them off
4) View LCD readout

Note: no instruction difference for cars (American) that supply power to outlets/cig lighters with ignition off vs. European cars (Jags) that do not have power till Ignition in On position.

My reading has been consistent, Red light & 12.2 V. Both with my 1.5 yr. old battery & surprisingly with my new replacement battery which
s/b fully charged. Even after driving 20-30 minutes no real change, as long as I let the battery sit overnight after the drive.

Tonight, I had a relative bring his multimeter. My battery (not disconnected but ,with nothing on except trunk lights) read 12.53V with the MM. That suggests it is fully charged & the .07 loss is probably due to the two trunk lights which are on by default with trunk open. I didn’t think to wait till the timer shuts them off. So, I think it is reasonable to use a fudge factor for my Innova tester of 0.33V for my Jag, maybe even 0.4 given the trunk lights. So, @ the cig socket 12.27 may be = 12.6 with MM @ battery. Using 0.4 FF, maybe my 12.2V reading = full charge.

I then tested his Ford Explorer. Since his power socket is live w/o turning ignition to ON, I just plugged it in. Reading = 12.6V! Then with multimeter (MM) @ his battery reading= 12.76V! So, even in this Typical American car with battery in the engine compartment & less distance to power outlet & no other computers, dashboard idiot lights on, there is a fudge factor of 0.16 using my tester.

I think I’ll keep it.

BTW, I wonder why, when using my tester to check the charging voltage @ 2500 RPM, I don’t see a corresponding drop of 0.33-0.4V?
Unless my alternator is really putting out 14.5-14.6V & the same fudge factor of 0.3-0.4 applies. No, I didn’t do the charging test with his MM.

P.S. I Love Tom Clancy Novels & also the films. “The Hunt For Red October” was great. (I prefer Harrison Ford As Jack Ryan vs. Alec Baldwin.)

 

BurgXK8,

THAT is the question!

FYI, I stopped by my Jag dealer & spoke to the service advisor I know (b4 my battery replacement) I explained my symptoms & he said it DOES appear to be the brake switch but, they would check to be sure b4 replacing it. (I have no OBD-2 codes) He did ask if the brake lights were working when it is displaying the FSEM light & the CC is not working but, I didn’t know.

It has not done the FSEM since 11-1-12 for some strange reason. (New battery 11-6-12)

I did have the CC fail for a few minutes & then back on again 2-3 x since then. But, not lately. I had long drives Tuesday & Thursday & no symptoms & that is when it usually has acted up.

 

Did you read the MAF fault with an OBD-2 reader?
My FSEM has come on with or w/o the CC on. So, not using the CC did NOT prevent the problem for me. CC must be tied into both accelerating & braking.

 

I had Jag Dealer replace the Brake switch 12-7-12. Will report back in a few weeks whether or not that fixed the FSEM/Cruise Control issue.
Had a ‘no start’ major problem 12-10-12 requiring a tow & being w/o my Jag till 12-14-12 so, not much drive time yet. (It was Fuel Pump & I’ll post separately on that issue soon)

RE brake pedal switch/sensor: LNB 6420BB. I almost tried to do it myself. I think the switch is harder to replace in the XK8 vs XJ8. With help from this forum I found it in my car & could reach it. I could clearly see the lower nut/bolt but, could not see the upper end & exactly how to attach it. I think a clip was involved & there was a correct & incorrect way to install that upper end. I would have had to do that by feel.

My service advisor (S.A.) a very nice, helpful guy, said he would replace it for 1/2 hr. labor ($72.50) + the part charge. No additional Diagnostic charge ($145) to verify that the issue was, in fact, the brake switch if I agreed to just pay to replace it. I was willing to take the chance & essentially pay $72.50 to avoid me crawling under that footwell & possibly installing the new part slightly incorrectly. Also, I believe I’d need a new size wrench to use on the smaller bolt & nut. Not sure but read that in these forums.

I had called Jaguar parts & was quoted $83 for the part in November. I called the morning of the repair visit & was quoted $154.02! wtf?! I told the guy weeks ago they said $83! He said 1st of every month they get new prices & it is not unusual to have price jump by that much, it is an older car, yada, yada, yada. I was irritated since, I had planed on ~$155.50 + tax T~ $163. I told my S.A. that the price jumped by a huge amount & he said something very interesting that some of you may wish to comment on.
He said different Parts people will quote different prices! There are actually 3 different prices for each part! MSRP or list price & a Unit price & 1 other (I forget what he called it, I don’t think it was wholesale price since why would any parts guy quote a wholesale price except to a mechanic or else in error) In this case he looked it up on his computer by the part # I gave him & had; a $83.50 price + a $124.50 price & a MSRP $154.02 price. He said he would work it to get me the $83 price. Great! When it was done he said the computer would not allow him to use the $83.50 price just the $124.50 price so he adjusted it with a discount!


So, Out the door, Total = $167.12. I’m very satisfied. Had I walked into the parts dept. I probably would have had to pay $154.02 + tax = 168.34. Then ended up cramped in that footwell for 4x as long as most people would take & probably having to use a crescent wrench & pliers or buy a new tool or 2. I was not be willing to buy a part like this on eBay since I would not trust that it was, in fact, new as claimed. To see if this part was the cause of my FSEM/CC problems, I need to be sure the part was new.

 

If you got a chance to see it, just curious if this is it:

brake switch

 

Yes, that is it. I have the old part.

 

4 weeks since brake switch replaced & no FSEM or CC failure! Problem seems solved!