Technical Tail lights not working

[Scotte72]

Hey,

A few months ago we got our daughter a 2105 500 Pop. It's been great until about a week ago one of the tail lights went. I easily replaced the bulb and was was fine for a another few days but just the other night both rear lights stop working. I've checked both bulbs and they appear fine and I've also replaced the fuse (5amp, in the engine compartment at position 87) but that didn't fix it. All other lights and indicators are working normally.
Can any of you knowledgeable folk suggest what my next steps should be? TIA.

 

[varesecrazy]

Hey,

A few months ago we got our daughter a 2105 500 Pop. It's been great until about a week ago one of the tail lights went. I easily replaced the bulb and was was fine for a another few days but just the other night both rear lights stop working. I've checked both bulbs and they appear fine and I've also replaced the fuse (5amp, in the engine compartment at position 87) but that didn't fix it. All other lights and indicators are working normally.
Can any of you knowledgeable folk suggest what my next steps should be? TIA.

Hi

On a 500.. Always worth checking the loom at the hatchback hinge

SEARCH
' Maybelline '
on here for Lots of info

 

[John202020]

Both rear lights, are the number plate lights on?
Isn't fuse 87 the reversing light?

 

[Scotte72]

Yes, the rear plate light is working fine. I got the fuse number from here:

Fuse Box Diagram Fiat 500 / 500C (2008-2019)

fuse--box-info.cdn.ampproject.org

But I just noticed 87 is for the pre 2013 model. Looking at the right table this time and it's interesting that there doesn't appear to be a specific fuse for the tail lights.

 

[John202020]

Ah, its going to be a bit more time consuming, do the brake indicators reversing and fog light all work as expected especially when all are on at once?
Have you got a multi meter?
Disconnect and re connect each cluster from the plug several times, confirm by testing each side light bulb(10w each) just put it on the battery with a bit wire.
Turn on the side lights key out, use you meter to see if there's any voltage on each cluster if both zero it suggests a break in the wiring inside the car, trace the loom back on the passenger side to where it divides to the boot lid ?

 

[Scotte72]

Thanks for the replies. All the rear lights appear to be working as expected (even al together) - the only exception is that the passenger brake light also doesn't work.
I do have multi-meter but TBH, I've never really used it so I'll google how to check that with the clusters (side lights on and key out).

 

[John202020]

Thanks for the replies. All the rear lights appear to be working as expected (even al together) - the only exception is that the passenger brake light also doesn't work.
I do have multi-meter but TBH, I've never really used it so I'll google how to check that with the clusters (side lights on and key out).

So the side lights are all ok? Great the only reason I say key out is that you can turn on just the side lights without having the engine running and the head lights on, which is useful when tracing issues.
Swap the reversing light bulb and the brake bulb over see if the brake light then works? https://www.eurocarparts.com/p/bosch-382-12v-21w-single-filament-bulb-single-bulb-481770099

 

[Scotte72]

Had another check and switched some of the bulbs. With the exception of both rear tail lights everything is fine and working as expected - all 3 break lights, indicators, reg light, fog light & reverse light. Is it strange that the brake lights work but the tail light don't? Obviously its the same bulb and unit.
I guess as per your suggestion the next step is to dig the multi-meter out start checking things - I just need to figure out how to do that

 

[John202020]

Had another check and switched some of the bulbs. With the exception of both rear tail lights everything is fine and working as expected - all 3 break lights, indicators, reg light, fog light & reverse light. Is it strange that the brake lights work but the tail light don't? Obviously its the same bulb and unit.
I guess as per your suggestion the next step is to dig the multi-meter out start checking things - I just need to figure out how to do that

No the side lights and brake light bulbs are different/separate bulbs unlike most other cars

 

[decappottabile]

Is it strange that the brake lights work but the tail light don't? Obviously its the same bulb and unit.

It's the same bulb, but the bulb has two filaments, one is 5 W (tail) and one is 21 W (brake) as you can see in the picture.
So you can't just put the fog or reverse bulb in there to test because they only have one 21 W filament.

 

[John202020]

It's the same bulb, but the bulb has two filaments, one is 5 W (tail) and one is 21 W (brake) as you can see in the picture.
So you can't just put the fog or reverse bulb in there to test because they only have one 21 W filament.
View attachment 433213

What year did they change it our 09 car definitely has two separate bulbs, ah looks like about 2015 it changed

 

[Ralf S.]

The bulbs could be suffering from a poor earth/connection etc. but for both sides to be out at the same time and all the other bulbs in each cluster to still be working sounds very unlikely. The car also hasn't complained about the bulbs being out (or at least the OP hasn't mentioned it) which suggests the brains thinks that either the lights are working normally, or that they're not switched on (which is the only time it checks whether they are or not).

If the BCM has one output wire that splits into two, then the likely candidate would be the wiring ahead of, or at the joint.. since for both spurs to have the same problem at the same time is unlikely. If there are two output wires from the BCM (left and right) then the problem is more likely to be the BCM itself, since it is the only "moving part" between the switch and the light bulbs.

I suspect it's the BCM (esp. if you have no "check bulb" warnings) in which case you need to identify the output pins, confirm whether they're live when the lights are on, and then if not, send the BCM to an ECU replace to have the circuit board repaired.


Ralf S.

 

[John202020]

I suspect it's the BCM (esp. if you have no "check bulb" warnings) in which case you need to identify the output pins, confirm whether they're live when the lights are on, and then if not, send the BCM to an ECU replace to have the circuit board repaired.


Ralf S

If the wiring is similar to the early cars then each light has its own feed back to the "fuse box" , you could well be right re the BCM

 

[Derbyfella]

Silly question, did you replace the original faulty bulb with exactly the same?
sure I ordered what I thought was the same when I had an issue previously and turned out to be wrong…could it have blown again….and the other side has blown due to old age like the first one….

 

[Scotte72]

Hi, Really appreciating all the advice. Update from this mornings tinkering.

1. The dash does report a warning saying "check parking light" so it knows something is up
2. New bulbs were used and tested. As decap points out further up it's the same light as the brake light and they are working fine.
3. I've no idea how to use my multimeter
4. I've not idea what a BCM is.

Is it worth getting cheap odb2 device for some diagnostics or just admit defeat and find a garage?

 

[varesecrazy]

Hi, Really appreciating all the advice. Update from this mornings tinkering.

1. The dash does report a warning saying "check parking light" so it knows something is up
2. New bulbs were used and tested. As decap points out further up it's the same light as the brake light and they are working fine.
3. I've no idea how to use my multimeter
4. I've not idea what a BCM is.

Is it worth getting cheap odb2 device for some diagnostics or just admit defeat and find a garage?

Looking like a cheaper fix at least

Tell us where you are based..

The best plug in diagnostics for this are FIAT SPECIFIC

Like MultiECUScan..
The forum has a register of users

 

[Scotte72]

Thanks for the link. I'm based in Edinburgh and, looking at the map, there is nothing anywhere close.

Is there no point in me getting a cheap obd2 unit from amazon and seeing what is says?

 

[The Panda Nut]

Silly question, did you replace the original faulty bulb with exactly the same?
sure I ordered what I thought was the same when I had an issue previously and turned out to be wrong…could it have blown again….and the other side has blown due to old age like the first one….

I agree with you about old age getting bulbs and one will follow another. I had a company car and at around 130K a headlamp bulb blew. In the space of one day 4 headlamps and both front fogs and 1 rear lamp failed. Thankfully Vauxhall leasing provided exceptional service and got it sorted at 18:30 hours on a dark wet freezing / foggy Friday night so I could do the last 110 miles home. I have also noticed there are a lot of bad cheap bulbs being sold these days, poor fit, filaments that are good but bulbs dont work and badly fitting bayonettes causing issues. Ive had ones that are too fat to fit the holder, ones that are too small and therefore loose, bayonettes that are bent broken and loose, and end caps on festoon bulbs. Never trust a new bulb to be good because its new or even if it works when wired to a test circuit. I have lost cound of the number of useless new bulbs I have bought in the last few years. Buy good brands, Osram hella etc and you should be OK.

BCM = Body control module. (A computery box that does body functions).
Cheap diagnostics are of limited use and generally I wouldnt go there as you might as well go buy MES andbe done with it. You cant fail to get your money back and its a re saleable item too.

 

[varesecrazy]

Thanks for the link. I'm based in Edinburgh and, looking at the map, there is nothing anywhere close.

Is there no point in me getting a cheap obd2 unit from amazon and seeing what is says?

@bri1232 shouldn't be too far away

 

[A3jeroen]

Silly question: You did not put the dual fillament bulbs (5W/21W) in the wrong way around?

gr J