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No Vehicle Reverse light


sharky6866
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I have a Mondeo Mk4.5 facelift and the reverse lights are not working, I have checked the reverse switch with Ohms meter for continuity = OK & the reverse bulbs are good, I have seen other posts stating that the reverse signal is handled from the BCM under the passenger foot-well, I have checked fuses and all seem good, everything else is working fine so this is baffling me, any help much appreciated.  

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3 minutes ago, sharky6866 said:

I have a Mondeo Mk4.5 facelift and the reverse lights are not working,

What year is the car (your profile says 2022, but I think that,s unlikely) ?

Remove both the reverse light lamps from the fitting at the same time and then measure the voltage at each of the lamp fittings with the car in reverse gear (engine OFF and ignition on). What voltage do you get ?

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On 9/30/2022 at 9:43 AM, unofix said:

What year is the car (your profile says 2022, but I think that,s unlikely) ?

Remove both the reverse light lamps from the fitting at the same time and then measure the voltage at each of the lamp fittings with the car in reverse gear (engine OFF and ignition on). What voltage do you get ?

Hi Unofix,

Thanks for the reply, It's a 62 plate, 2012 Mondeo, I'll give it a go when I get the time.

 

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8 hours ago, sharky6866 said:

Hi Unofix,

Thanks for the reply, It's a 62 plate, 2012 Mondeo, I'll give it a go when I get the time.

 

I seem to have the same problem as yours. I just changed the reverse light switch few mins ago, checked both reverse light bulbs (visual inspection and looks fine) but no luck. It would be good to see what you find with yours. Please keep updating us.

Will a single faulty bulb (either side) stop both lights working? I have a parking sensor connected directly to one of the wire and that is what made me aware that reverse light has stopped working.

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2 hours ago, sahilsaid said:

Will a single faulty bulb (either side) stop both lights working? I have a parking sensor connected directly to one of the wire and that is what made me aware that reverse light has stopped working.

Disconnect the wire for the parking sensors from the reverse light and see if they work. If on your car the reverse light circuit is controlled by the BCM then it may be sensing the increased current draw and is switching off the supply to the lights.

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12 hours ago, unofix said:

Disconnect the wire for the parking sensors from the reverse light and see if they work. If on your car the reverse light circuit is controlled by the BCM then it may be sensing the increased current draw and is switching off the supply to the lights.

I already tried removing the parking sensor's connection completely. The parking sensors worked fine for over 3 years.

 

I connected parking sensor to brake light and it seems to work fine just to confirm the parking sensor's controller unit is not faulty.

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29 minutes ago, sahilsaid said:

I connected parking sensor to brake light and it seems to work fine just to confirm the parking sensor's controller unit is not faulty.

So just to clarify the situation. When you reconnect the parking sensors back to the reverse light circuit as you had them, do the sensors still work even though the revers lights don't work ?

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1 minute ago, unofix said:

So just to clarify the situation. When you reconnect the parking sensors back to the reverse light circuit as you had them, do the sensors still work even though the revers lights don't work ?

No, nothing works. Both reverse lights and sensors are not getting the voltage.

I checked the voltage on the reverse light switch (below battery in bonnet before replacing the switch) and it gets the 12V power.

 

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If you remove the connection to the reverse light switch and short the wires in the plug together, do the reverse lights come on ? (remember to have the ignition turned on).

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13 minutes ago, unofix said:

If you remove the connection to the reverse light switch and short the wires in the plug together, do the reverse lights come on ? (remember to have the ignition turned on).

Let me try this today later on (after work) and see how it goes. Thanks

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I had a another go today but still no luck :sad:

  • Shorted the wires in the plug together to eliminate the reverse light switch. This did nothing (Photo attached)
  • Verified the 12V (11.5V) in multi meter is being recorded from the in the reverse light plug.
  • Confirmed that the reverse light switch is working by checking its continuity in multi meter.

In my opinion, above three items confirm that things are fine under the bonnet but something else is stopping the current before it reaches the reverse light at the back. Not sure where to go next with this tbh.

1665343582577.jpg

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Looks like it's an issue with the Body Control Module (BCM)

I don't have the wiring schematic for your model but as far as I remember the signal from the reverse light switch is sent to the BCM which then sends the power to the reverse lights.

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  • 2 weeks later...

Hello back, I can confirm it is the BCM under the passenger foot-well, this will require replacement and also all the keys to the car will require re-programming because of this. I’m very disappointed as this could be an issue with the facelift models, a refurb unit could be purchased from eBay with a warranty just make sure you have the correct part, mine was (BG9T-14A077-BL) but as I say things will require be reprogrammed and also tested so no faults occur with the refurb unit. It looks like a very costly thing for something as simple as a reverse light Issue.

20220914_103016.jpg

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If the only problem is the reverse lights, and everything else is working fine then the circuit can be repaired using a relay.

Any decent auto electrician should be able to disconnect the reverse signal from the BCM and use it to control a relay coil. The wire to the reverse lights on the BCM will also need disconnected and rerouted  to go via the contacts on the new relay. It should only take an hour and a £8 relay and the job will be finished.

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27 minutes ago, unofix said:

If the only problem is the reverse lights, and everything else is working fine then the circuit can be repaired using a relay.

Any decent auto electrician should be able to disconnect the reverse signal from the BCM and use it to control a relay coil. The wire to the reverse lights on the BCM will also need disconnected and rerouted  to go via the contacts on the new relay. It should only take an hour and a £8 relay and the job will be finished.

Yes, good point unofix, I wonder what plug it is on the BCM and what’s the wire colours, also I would be interested if anyone else has taken this route?

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As I've said, unfortunately I don't have the schematics for your model.

This is just a pure guess based on similar models. The connector on the BCM for the wires going to the reverse lights might be "C2280F" possibly pin 11 which could be a blue and white wire.

I've no information on the wire from the reverse light switch but you could probably work that out testing the wire from the switch to the BCM with a multimeter.

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  • 2 months later...

Well, if you read it though properly Sharkt said it was the body control module in his case, but youll have to do some of the checks outlined in this thread to eliminate the basic causes. 

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  • 4 weeks later...
On 10/19/2022 at 1:41 PM, unofix said:

If the only problem is the reverse lights, and everything else is working fine then the circuit can be repaired using a relay.

Any decent auto electrician should be able to disconnect the reverse signal from the BCM and use it to control a relay coil. The wire to the reverse lights on the BCM will also need disconnected and rerouted  to go via the contacts on the new relay. It should only take an hour and a £8 relay and the job will be finished.

Hey Unofix
Thanks a lot for your detailed answers and time to answer these queries.


I think this video on youtube talks about the same issue in these models.


Do you mind explaining the solution you propose in more details please. From your answer, it seems like it is not something that can be attempted by a non-technician person, correct? The Mk4 models in 2023 are not worth too much so spending a lot of money to get reverse light working is not justifiable. 

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Hello Sahil,

The original factory fitted reverse light system is controlled by the BCM. Just think of it as a mini computer. When you select reverse gear a signal is sent from the switch on the gearbox to the BCM, and provided the ignition circuit is on, it will then output a positive feed on the wire that goes to the reverse light, and hey presto the light comes on !!

Using a fairly standard single pole 12volt automotive relay the exact same can be achieved. The wire from the reverse light switch on the gearbox needs disconnected from the BCM, and the wire from the BCM to the reverse lights also needs disconnected.

Using a relay the wire from the gearbox switch is connected to one of the coil connections of the relay. The wire to the reverse lights is then connected to the normally open contact (NO) of the relay.

Now depending on how the switch on your gearbox is working, it is either supplying a positive supply to the coil of the newly fitted relay (most probably) or it is supplying a negative connection. Assuming the first option then all that needs to be done now is to connect the other side of the relay coil to a permanent earth (negative), any suitable bit of metalwork that you can attach a wire to will do.

Lastly, the common connection of the relay contacts (C) needs to be connected to a positive supply that is only live when the ignition is on. The End. 👍

Happy new reverse lights !

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9 minutes ago, unofix said:

Hello Sahil,

The original factory fitted reverse light system is controlled by the BCM. Just think of it as a mini computer. When you select reverse gear a signal is sent from the switch on the gearbox to the BCM, and provided the ignition circuit is on, it will then output a positive feed on the wire that goes to the reverse light, and hey presto the light comes on !!

 

Amazing explanation. Many thanks.

I have the idea now. I will use the multimeter to find which cable it is in BCM that gets the power when reverse gear is selected.

Can you please send me a link to relay please. Is something like below okay?

image.thumb.png.2d4a565d88672c61c9aca1cfbb27cbd4.png

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Example of basic single pole relay as sold by Halfords

https://www.halfords.com/motoring/tools/fuses-electricals-and-fixings/electricals/halfords-hef554-relay-12v-30amp-4-pin-184013.html

Coil connections are pins 85 & 86

Connect a switched live supply (must be able to supply at least 15 Amp) to pin 30

Connect the wire to the reverse lights to pin 87

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It could be misleading to measure the volts at the reversing switch....IF the reverse switch just completes the circuit to earth/chassis return, (as might be the case) and that part of the cct is broken (ie the wire that connects from the switch to chassis-if that's how the cct is completed) then you WILL get full volts on the switch, 'cos no current is flowing so you're seeing no volt drop across the bulbs. It would be better to use a test bulb from the reverse switch to chassis to see if it and the reversing bulbs light up, I'm thinking.  (just thinking outside the box) .... 🤔

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