I bought a cheap aftermarket camera. There were others that look more like OEM but they were not being sold domestically. Shipping from China has been unreliable so I went with what I could find. A couple of eBay sellers had a better one and claimed to be shipping from Pennsylvania, but their feedback is full of claims that it shipped from China.

It works fine when I start the car and put it in reverse. The screen is scrambled when I shift into reverse after driving forward. It starts to work again after I turn off the car, turn it back on (with or without starting), and put it into reverse.

I put COMAND into engineering mode and set it to view the backup camera. The signal cuts out as expected when shifting out of reverse since it is powered by the reverse lights.

I ensured that it is not getting any power when the reverse lamps are off.

I see two options:

1. Get it swapped and try another.
2. Wire it to a circuit that is powered when the car is on - don't intermittently power it with the reverse lights.

Has anybody seen this behavior?

 

You're troubleshooting an aftermarket no-name camera that scrambles video shortly after working once every time key is cycled.


Try couple things if you will....:

1- different routing path for your video harness on driver side.

2- use a different ground point to body (not trunk lid).

3- disconnect Comand to see if input still affected without Cam driving its signal.

4- 50/60Hz video refresh compatible.
5- play the video signal level specs.

6- what video standard... compatible??

7- why not buy a used RFK from eBay!

 

Thanks for the ideas!
That sounds like a lot of work. I'm going to try that one last.
I did use a portable DVD player's composite output as a video source in the trunk using the 6m RCA extension cable. The picture was clear without any glitches.

I spliced into the ground for the backup lights, so the camera's power is connected in parallel with the incandescent reverse lamps.

I only get a black screen when this is not connected. The DVD player was clear.
The camera listing does not list this specification. There definitely isn't any configuration setting on the camera itself. Getting a clear screen at all means that everything is matched up as NTSC, which I believe is only 60Hz
A 10Hz clock slip would take less than five seconds to show in the video quality.
Google didn't find that for me. Is that something I can query via the engineering mode?
I believe everything this NTSC. Getting just one moment of clear video means that it is matching up.

Not sure if serious that looks to be over 10x the cost and also looks like it may require module programming. I looked into using OEM and was quickly scared off by the cost.

 

Based on your inputs, I'd concentrate on :
#1: Routing path.
#2: Clean GND.

 

Rwagz wrote :
I spliced into the ground for the backup lights, so the camera's power is connected in parallel with the incandescent reverse lamps.

I assume the text in red means you are also getting positive 12V from the reverse lamp correct ? I mean your plus/minus 12V supply both are from the reverse lamp.
If possible avoid using "POWER" to represent positive 12V because some devices in the car is Ground side switched and not only at positive side.
Power is only available if Plus and Minus 12V get connected, technically both can be called POWER.

So, I am still assuming you camera is purely powered by the reverse lamp.
Camera can take few watts of power. Rear SAM may not allow it to happen, because rear lamp may be seen as overload....higher amperage than specified.
Get a buddy to help to see the reverse lamp activation :
01. 1st time getting into reverse gear, camera will power up as you said...fine. Keep it running for 30 seconds. Back in neutral. Engine still running.
02. Do reverse again,the camera supposedly won't turn on correct ? Get ur buddy to see , did the reverse lamp also failed to turn ON ?

If no 02 is also a dead reverse lamp as a result........... well , you now know why.


The rear SAM will reboot and re-investigate after every key cycle. So that is why your camera can work again after key OFF and then key ON.

 

Have a look at doc# AN54.65-P-0030-03EW titled "Retrofit the backup camera wiring harness"
for inspiration on power source vs. trigger source.

You may need to use a low power SSR relay to mirror 'backup light" signal while tapping R-SAM for power.

 

Thank you for that insightful troubleshooting. The reverse lamps were always lit.

TLDR; I believe that engine noise/interference was causing the camera to malfunction, but only on the reverse lamp circuit.

So it was the camera, the signal cable, or the power source.

Camera: The replacement camera behaved in the same manner.

Signal Cable: I ran the new camera's cable from the trunk through the open window and the problem was unchanged. I double-checked the fakra connector and it appeared to be the cause! so I was disappointed when the problem continued. The problem was coincidental with me wiggling the fakra connector.

Power: It turns out the reverse lamp power was good for the camera when the car was turned on without the engine started. Starting the engine caused it to scramble.

Power reads 12V with or without the engine running. I doubt it is voltage drop because a running engine will only help with voltage.

I used a spare 12V battery to power the camera independently from the car and it worked great. I double-checked that I was using the two wires for the reverse lamp by using a continuity checker from the bulb socket to the electrical connector. only two of the connector's wires had continuity with the reverse lamp socket. Weird.

I'm guessing it was interference from the engine. Nothing else is screwy with the electrical system. The starter battery and the "dash battery" are both new.

Maybe adding a capacitor would help clean up the power. I could also add a relay I didn't want to mess with it much more. I extended the power feed to the trunk-mounted 12V convenience receptacle. The receptacle is not powered when the car is off.

That was a huge pain. I'm putting all of this here in case somebody else runs into the same problem. My own searches didn't turn up anything useful.

I'm open to alternate theories about what went wrong here.

 

R wrote :
Power: It turns out the reverse lamp power was good for the camera when the car was turned on without the engine started. Starting the engine caused it to scramble.
Expected, as starting the engine will cause power to dip to 10ish volt and camera may reset.

R wrote :
I used a spare 12V battery to power the camera independently from the car and it worked great. I double-checked that I was using the two wires for the reverse lamp by using a continuity checker from the bulb socket to the electrical connector.
I assume when you use a spare battery, the spare battery for testing is using shorter run power cable to camera power input compared to when using reverse light ...yes ?
Try to measure loaded voltage at camera power input when using both these power sources, surely higher voltage or less voltage DROP while loaded/camera-on will be better for camera.
Continuity testing is not so good compared to a loaded test , example using a suitable amperage light bulb* (*camera in your case) as a load .
In your case tapping power from reverse light, a loaded state would be reverse light ON and camera ON.


BTW, how does the factory COMAND screen recognize video input and auto-select the input to that reverse camera video feed ?
Sorry, me no back up camera

If you have a simple monitor with that yellow RCA video input you can use it to test, this way you can eliminate the possible issue of factory COMAND screen is the one not wanting to accept the video feed.

Video signal wire and connector. You speak of Fakra.
Signal drop at video cable is also a possibility, more so when cable used is so tiny/thin. In my Villa CCTV, I still use analog one.... not IP-based camera and uses coax as video cable.
Longest running coax cable is at 35 meters ( 115 feet ). I choose real good brand and thick to get lowest signal drop or dB loss and I use a good Belden connector.


If you worry about "noise". The fuel tank has a 3 phase PWM fuel pump controller called N118. It is near pillar C under the rear seat ( google it ), that unit may produce noise due to its PWM throttling.


WARNING FOR RELAY.
When you have to use a relay, get one which has resistor or diode to kill/absorb of voltage spike. https://mbworld.org/forums/e-class-w...-not-know.html


Good luck.........

 

Disconnecting the camera leads and reconnecting them with the engine running didn't return it to proper operation. That same voltage drop would apply to any circuit, not just the backup lamps.

The spare battery had a longer cable. The reverse lamp and the camera are both mounted on the trunk lid. I had to add a jumper to connect the battery. We're talking a voltage drop difference in at most two feet of wire.
The power wires for the camera were a much smaller diameter. This camera likely does not draw much.
My finished job added a few feet of small gauge speaker wire to extend the power wires across the trunk mounting arms and back to the power receptacle.
The continuity test was only to identify the exact wires that were powering the reverse lamp.
I never bothered to measure load with an ammeter. I could have pulled the reverse bulb to see if the camera works with only the camera's load on reverse light.
[/QUOTE]
.

I'm confused here. Are you asking me? If so -
I used the engineering menu option to view the cameras, then ran the fakra connector across the connections until something showed up. I used a DVD player as a source when I didn't trust that the camera was working.
It was one of the green connectors, left-most from the driver's position facing forward.

I had an ancient Dell monitor that has a composite input that I used to test my sources. I also used a portable DVD player as a test source..

The included cable is 6M long. I had two cables to try and they behaved the same. My DVD source in the trunk and the camera it self (properly powered) show up fine..

I ran another coaxial cable outside the car and in through the window to eliminate noise sources. It was definitely happening only when the engine was running.

Thanks. I got it working off of an ACC switched source in the trunk. I gave up on using the reverse lamp circuit. I have no idea why that circuit is noisy or why the camera is susceptible to it.

 

Good to hear u got it sorted out.

I think now I know why the reverse lamp is so "noisy' , it is not switched by a simple relay. It is electronically switched using driver/transistor. That is also how it can detect and safely ignore short circuit and show warning if using LED bulb ( if car comes with incandecent bulb )
I guess the noise is the diagnostic signal those wires carry.

Attached a Rear SAM fuse assignment, there is a back up camera fuse prepared by MB for certain option code. Fuse 84 slot.
It is 30g power source, meaning power is only available when and if the car computer wakes up , merely opening a door and without key in slot, many computers will wake up.

30g
Starts at F32 PreFuse Block. 30g is the output of K2 relay at F32.
Only 2 power lines served by K2 for W212, MR2 with F162 of 150 amps to Front SAM terminal 8S and IG1 with F163 of 150 amps to Rear SAM terminal 2V.

I have not mapped out my Rear SAM actual fuse assignment yet, unlikely my front SAM which I know very well and have it mapped out as per my car.
I took a peek at the wiring diagram just now, MB factory reverse camera also takes reverse lamp +12V as activation signal to N66/10 reverse camera module.

 

That's better than any explanation I could muster. When wired to the reverse lamp, the video was clear when I had the ignition ON (engine not started) and the transmission in reverse. I'm not sure why the engine running causes so many issues.

In the wiring diagram - what are the power paths for the reverse lamps? Which component provides power? Is there a fuse in that circuit?

Thanks for your help and insight.

The worst part of this is that I put it 100% back together because it was working, then the test drive showed this. I had to wait a few days to get another camera for troubleshooting.

During my troubleshooting I connected the camera's negative power lead to the 12V convenience receptacle ground. Connecting the positive lead had these results:

• Convenience outlet's (+) : works with or without the engine running. I'm glad this is ACC switched else I'd have to find another source somewhere.
• Reverse lamp (+)
  • Works without engine running
  • Scrambles with engine running.

This is truly strange. Troubleshooting is one of my strong suits and this one kept be busy until I had a second source, camera, screen and cable. Power was the last on my list.

 

Rear SAM, complete package.
Total has 10 + 1 sheets & others and for Sheet #10 the reverse light location, I re-print and scale it to 30% so that you can zoom to read easy , but without having to deal with too many pages per sheet.
My WIS print out skill is poor, it is XPS ... LOL. I hate wiring diagram being cut into pages.

I give you also N66/10 diaghram, MB own reverse camera module.

Pay attention to the date of car manufactured ( not model year ) and option code, to use the correct section of the diagram. It is so full of information from so many variants MB offer, so delete what is not related to your car year, option dan etc.
Its a pain in the azz to use MB original diagram due to so much information per sheet from so many engine/year/option code variants
If you have not already, get your car Data Card from online VIN decoder, Data Card is neeeded to know option code numbers you car has.

If you need a better zoom-able sheet, let me know which number you need.
They are all different sizes, so I can't print 1 scale to fit all, unless I choose 100% scaling and then 1 sheet can be like 8 pages..... hahahaha.

I believe your car with non LED rear lamp is below, up to Feb 2013 ( --->02/13




Example of diagnostic signal Engine computer sending to its sensors/devices when engine is OFF. I never scoped the rear SAM for its rear lights sets, but I guarantee Rear SAM will send out those diagnostic signals too.
https://mbworld.org/forums/e-class-w...ml#post8535067



have fun.....