Hi all,
In my seemingly never-ending quest to get rid of the 'Rear Bulb Fail' dash message, I finally got around to opening up the lamp module to work out what it actually does.

From that, a few observations:

1) A missing/blown bulb isn't sensed until it's powered on.

2) The number plate and rear side markers, although fed from the module, aren't monitored by it.

3) It produces a single logic output that is fed to the SLCM

4) Even allowing for development IPR, tooling, component and building costs, it's one expensive bit of simple electronics.

Oh - and Visio isn't a very good tool for creating circuit diagrams.

I've attached a pdf of the internals of the module and a list of the connections in case anyone needs to repair one. I know it's eliminated in later cars as the functionality is integrated into the SLCM, although I expect the design will be very similar.


In my case the problem must be further along the chain as there's no obvious issue with the LCM, and the dash message appears as soon as the ignition is turned on. LED lamps are becoming increasingly tempting

Mike

 

Michael, have you added the auxiliary ground to your lamp housing?


Wayne

 

+1, here is the link on adding the ground: https://www.jaguarforums.com/forum/x...esolved-35083/

Nice work documenting the circuit !

 

+1

Thanks for the thorough documentation.

After the experiments with LED lights and sorting through just how much of a load keeps the system happy, I had been wondering just exactly how it was checking.

Makes me want to crack open the SLCM and see if it's the same.

 

Thanks CJD and WhiteXKR for the info on the extra grounding. The error first showed up after the car's last dealer service where they replaced one of the tail bulbs. After fiddling with lots of different bulbs with no result other than a horde that will outlast me, I checked the connectors, but everything looked pristine. That and the fact that the symptoms seem somewhat different led me to the electronics, and what I've discovered seems to bear this out.

However, Occam's razor belatedly springs to mind here so I'll try the grounding as a next move.

Charlie, as the integrated SLCM does the same job (among others) I'd expect the guts to be very similar. Without too much technobabble, there's only a single logic 0 or 1 output signal so it's a case of rigging the system by either faking the correct one or fooling it into not noticing a missing/incorrect load for any bulbs that you may wish to replace with LED: shorting out the relevant low-value series resistor is one way.

If the grounding doesn't cure I'll have a stab at reverse engineering the SLCM and post the results.

Anyway, I've waffled enough, so thanks again guys: this forum is awesome - like having a personal team of wizards.

Mike


Just discovered after 11 years that there's a stash of spare fuses on the reverse of the lid. No wonder I failed Police Academy.

 

Just to close this out, OCD finally overtook CBA and I had a little spare time to revisit the issue.

Ultimately, it was the lamp control module causing the 'rear bulb fail' warning:- replacing a leaky transistor (TR4) means I now see the odometer reading instead of the permanent message.

IMO lamp monitoring is a solution to a non-problem, and a pain nowadays because of the need to trick the system so that incandescent lamps can be replaced with their modern LED equivalents.
I've opted to 'keep it original' for the time being, but it is possible to defeat the module's functionality so that ordinary non 'canbus' LED lamps can be fitted without the need for load resistors. If anyone is interested I'd be happy to provide details, although note this won't work for the indicators as they're managed by the BPM.

 

Apologies for bumping up an old thread, but i'm fitting leds in the rear lights and have the canbus error.
I'm aware some have soldered load resistors to the busbars to resolve the issue.
Personally, i'm not a fan of installing resistors as they get hot, and there's a poor ground on the light as it is.
Can't see the insurance company being happy about it.
maybe fooling the canbus signal is the way to go.

Michaelh, can you provide details on how to stop the rear bulb fail message please.
I've fixed the indicator leds without the hyperflash, and done the brake bulb mod as shown on Rick "never going to give you up" Astleys youtube channel.
The reverse and fog lights are non canbus so are sorted. It's just this 1157 brake led that's giving me jip.

Is it true you cut the red wire in the LCM and ground it,
I have a 2004 xkr and i believe on later cars the LCM is integrated with the SLCM.
Cheers.

 

Michael, you are a brilliant, brilliant man! I have four or five lamp control modules, mostly burnt up or cannibalized before realizing someone had replaced the lamp modules (which resulting in all the melting) with a different model year..

I still have a permanent passenger side light on, because I bodged my last lamp module without the benefit of a schematic.

Hopefully your schematic will save me another 35 bucks or so and help preserve the supply of eBay lamp control modules for the next unwitting victim!

 

Hi sossybaby,
Sorry, I can't help on the 2001 & newer cars as the lamp sensing was integrated into the SLM from then on as you state.The later SLM works in a similar way, but I don't have access to one to reverse engineer a solution.

I agree with you re resistor loading:- heat (particularly in the brake lamp circuit) and no reduced current draw.



Did you determine in the end whether your car has had the later lamp clusters fitted? That would have some bearing on the tail lamp fails if so.

With hindsight, it would have been helpful had I included the circuit board references as it would be considerably easier to follow. I do need to revisit this at some point.

 

I'm 99% sure the later lamp clusters were fitted because there is a dual filament light in the outside position and a higher wattage lamp in the middle. From what you have advised, that is not correct for a '97 coupe.

My short term solution has been to eliminate the middle lamp (which reduced the load) and run the fog lamps for extra illumination.

So far, and thanks to your help, I haven't burnt a fuse or the latest lamp module. Which is saying something and brings me great joy !

Once I get (time) to get the wiring right (a wiring position is swapped on the left side), I'll try lower wattage bulbs in the center position. And of course, refer to your schematic and re-bodge the lamp control module to eliminate that right side "running" lamp. Not sure that's going to eliminate the "Rear Lamp Fail" (or some such) warning in the dash, but I know there are other threads (or perhaps your schematic) which will rid me of that issue.

Thanks again !

Stay warm ! (Perhaps I am transferring our somewhat icy, but not dire situation on the East Coast of the US to yours in Jersey Channel Islands, as Wikipedia says you enjoy mild winters !)

 

Later lamp cluster has the chrome bezel around the outside of the lens, and the connector faces toward the front of the car rather than downwards. I'm sure you'll get there

We don't often get sub-zero temps, thankfully, although we did have a fairly cold spell a couple of weeks ago that coincided with the heating going on the fritz for a few days...