Electrical issue when shifting into reverse

[JDMac34]

I know that my car has had a...colorful...history, but for the most part I haven't noticed anything to show it other that a really worn steering wheel, some hardware store hose clamps, and duct tape under the hood. The other day I noticed something new that I'm not sure how to attack.

My car is a 2011 Mustang GT Premium with a manual transmission. Whenever I shift into reverse, I noticed that my ambient lighting (floorboard and cupholder lights) turn off. That doesn't really bother me, but I discovered that I also don't have brake lights or reverse lights when I shift into reverse. The brake lights work fine in all other gears, and I still have the running lights at night, but they won't get brighter to alert drivers that I am actually hitting the brakes.

Has anybody else had an issue like this?

 

[Iceman62]

I hate electrical gremlins...do you know if the tranny's original, or been worked on? Any other electrical mods to throw in the mix.

I can only guess there's a bad sensor, or wire/ground somewhere that's not sending signal to the lights when in R.

 

[redfirepearlgt]

smart junction box and/or body module B would be my initial thought looking briefly at the 2011 schematics without doing any diagnostics. The body module is common to the brake, reverse, interior lights you mentioned. The Smart Junction Box is common to everything you are having issues with.

If you are serious at hunting this down and have knowledge of using a multimeter and electrical troubleshooting (test lights won't suffice in this problem) let me know. We can try to isolate it. If you are just gathering information before taking it to a service shop there is no reason to dig further.

 

[JDMac34]

I hate electrical gremlins...do you know if the tranny's original, or been worked on? Any other electrical mods to throw in the mix.

I can only guess there's a bad sensor, or wire/ground somewhere that's not sending signal to the lights when in R.

I know that the transmission has been replaced recently. As far as I know, there aren't any other electrical mods. I'm hoping that it's as simple as a ground missing somewhere

 

[JDMac34]

smart junction box and/or body module B would be my initial thought looking briefly at the 2011 schematics without doing any diagnostics. The body module is common to the brake, reverse, interior lights you mentioned. The Smart Junction Box is common to everything you are having issues with.

If you are serious at hunting this down and have knowledge of using a multimeter and electrical troubleshooting (test lights won't suffice in this problem) let me know. We can try to isolate it. If you are just gathering information before taking it to a service shop there is no reason to dig further.

My plan is to hunt this down on my own. I can't say that I have much experience with electrical troubleshooting but was hoping that somebody on here might have had something similar happen and could point me in a certain direction to save some time.

The first thing I was going to do was to pull the tail lights out and see if there was a missing plug or wire pulled out or anything simple like that. The brake and reverse lights are more of a concern to me than the ambient lights, but I don't see how those would be connected.

 

[Juice]

Get Forscan, do not need license to use for diagnostics.
Read codes from the SJB, and, you can verify the SJB is registering the brake pedal being pressed (to activate brake lights)
Thats where I would start.

An easy test would be cruise control. If working, does hitting the brakes shut cruise off? This would confirm the brake light switch working, and pcm getting the brakes on signal.

 

[JDMac34]

Get Forscan, do not need license to use for diagnostics.
Read codes from the SJB, and, you can verify the SJB is registering the brake pedal being pressed (to activate brake lights)
Thats where I would start.

An easy test would be cruise control. If working, does hitting the brakes shut cruise off? This would confirm the brake light switch working, and pcm getting the brakes on signal.

Brake light switch works because I have brake lights whenever I'm not shifted into reverse. I had my car hooked up to Forscan earlier and it didn't show any codes for anything electrical, but I'll double-check that. Thanks for the suggestion

 

[pass1over]

with forscan, check PID

BOO1 - it should show brake pedal on/off status

 

[redfirepearlgt]

My plan is to hunt this down on my own. I can't say that I have much experience with electrical troubleshooting but was hoping that somebody on here might have had something similar happen and could point me in a certain direction to save some time.

The first thing I was going to do was to pull the tail lights out and see if there was a missing plug or wire pulled out or anything simple like that. The brake and reverse lights are more of a concern to me than the ambient lights, but I don't see how those would be connected.

Good luck....but I would bet a 12 pack of Dr Pepper you will not find anything there. Each tail light uses its own separate ground, (G400 left, G402 right) and if either was open path you wouldn't even get a reverse light or tail lamp illumination. Of course this is assuming the car has never been compromised...meaning never majorly altered as a purely track car or totalled out and then salvage titled. If either of these be the case all bets are off, there will be no logic in troubleshooting and it could be anything.

I would be curious to know if when the brake lights do work are they actually BRIGHT like they should be? Or do the simply come on when you press the brake pedal?

When you have an issue like you are describing that effects multiple systems you have to look at what is in common with them all. I stand by my initial guess given the car has never been compromised, and you are unable to go into any more in depth electrical troubleshooting. Best of luck. Hopefully you will post the resolve.

Definitely more able to isolate with forescan and a laptop...of course you need the USB to OBD2 interface device as well as the free software down load. I am not certain if forescan will work through an HP tuner port, or SCT device linked to a laptop. Some real sharp guys on here with that fancy stuff if you have the means to access it.

 

[Juice]

Forscan, to my knowledge, will work with elm327 adapters over wifi, BT, and usb. I have also gotten it to work with the IDS pass through device, but its a bitch and offers no benefit over elm327 adapters.

 

[pass1over]

I've used FORscan on my car with a BT Kiwi 2 dongle and my android phone. I've also used an OBDLink EX USB connector and my laptop. So I know these 2 devices will work with FORscan for sure.

 

[redfirepearlgt]

Forscan, to my knowledge, will work with elm327 adapters over wifi, BT, and usb. I have also gotten it to work with the IDS pass through device, but its a bitch and offers no benefit over elm327 adapters.

so you're saying that i can connect my laptop directly to sync, and access the obd canbus network with forscan in that manner without a usb obd2 device?

 

[Juice]

so you're saying that i can connect my laptop directly to sync, and access the obd canbus network with forscan in that manner without a usb obd2 device?

Need an elm327 device.

 

[redfirepearlgt]

^^^ OK. Thanks. Just always been very skeptical of freeware and using it to tie into a major investment. I'm looking into this more closely. THanks.

 

[Juice]

Elm327 can be had for around $20. I prefer wired USB adapters. You will need one with HS/MS switch or one that will switch automatically. The sjb is on the MS can, pcm is on HS can bus.
Forscan is not free IMO, need license to make changes. Diagnostics function without a license.

 

[pass1over]

Elm327 can be had for around $20. I prefer wired USB adapters. You will need one with HS/MS switch or one that will switch automatically. The sjb is on the MS can, pcm is on HS can bus.
Forscan is not free IMO, need license to make changes. Diagnostics function without a license.

beware of cheap USB elm27 devices, they wont always communicate fast enough or be capable of FORscan's full potential

 

[Juice]

beware of cheap USB elm27 devices, they wont always communicate fast enough or be capable of FORscan's full potential

Oh, I know. lol
My Wifi elm wont program. No issues w/wired elm. My BT elm came with Torque, and, only works with Torque.