Any electrical geniuses on here could help? I have a w176 with an intermittent fault on the parktronic. B12851C: Front distance sensors have a malfunction. The voltage is outside the permissable range. (Sometimes also appears) U110100: Communication with rear warning indicator malfunction.(Sometimes also appears) U112B00: Communication with front warning indicator malfunction. Changed:All front parking sensors and harness.Used parktronic module from ebay.
Tested voltage at harness plug, all good but fault is intermittent and I can't replicate it. Currently considering another used module or running new 12v and gnd cables between module and front harness. If anyone has any pointers where I can look or tests it would he much appreciated. TIA 😊
Sounds like it could be many things, perhaps it might be a connection problem - you mention a voltage problem. I have a bit of insight in testing voltage and current continuity from working on and resolving pesky telecom cable faults.
You can try checking the resistance of all wires and connections in the circuit.
Ensure no voltage is present in the system when doing resistance measurements.
First and foremost, ground wires, source voltage wires, and signal wires must be connected tightly, with no corrosion.
Secondly, check where wires go in to the pins in connectors. The crimp where each pin connects to a wire must be formed nicely, and must be tightly connected to the wire strands. The wire should not pull out of the pins with a gentle tug. If it really gets difficult, use an ohm meter to check for continuity in each wire - measure between pins on each end of each wire, the resistance value should be very low.
Thirdly, make sure connectors fit together tightly and no pins in the connectors push out of place - each pin in each connector should be pushed into its position fully and not come out of place.
Next comes what I call the wiggle test (note the high tech term, ha ha). With everything connected and energized, begin wiggling the wires a little bit to see if you can make the failure happen. If you can reliably make the failure occur when wiggling in a specific place, you have likely found where a connection problem is. Fix any bad or broken connections.
I always left a little slack in wiring looms used in manufacturing cables to try to avoid just this problem. There are many ways you can make a poor connection when putting a cable together in a factory that will only show up later.
Hope this helps a little bit, I don't know about all the specialty testers used here but I always start with a physical check.
Sounds like it could be many things, perhaps it might be a connection problem - you mention a voltage problem. I have a bit of insight in testing voltage and current continuity from working on and resolving pesky telecom cable faults.
You can try checking the resistance of all wires and connections in the circuit.
Ensure no voltage is present in the system when doing resistance measurements.
First and foremost, ground wires, source voltage wires, and signal wires must be connected tightly, with no corrosion.
Secondly, check where wires go in to the pins in connectors. The crimp where each pin connects to a wire must be formed nicely, and must be tightly connected to the wire strands. The wire should not pull out of the pins with a gentle tug. If it really gets difficult, use an ohm meter to check for continuity in each wire - measure between pins on each end of each wire, the resistance value should be very low.
Thirdly, make sure connectors fit together tightly and no pins in the connectors push out of place - each pin in each connector should be pushed into its position fully and not come out of place.
Next comes what I call the wiggle test (note the high tech term, ha ha). With everything connected and energized, begin wiggling the wires a little bit to see if you can make the failure happen. If you can reliably make the failure occur when wiggling in a specific place, you have likely found where a connection problem is. Fix any bad or broken connections.
I always left a little slack in wiring looms used in manufacturing cables to try to avoid just this problem. There are many ways you can make a poor connection when putting a cable together in a factory that will only show up later.
Hope this helps a little bit, I don't know about all the specialty testers used here but I always start with a physical check.
All the best.
Thank you for the detailed response!
All cables seem to be 0.1-0.2ohms end to end.
I also wiggles all the connections with the meter connected and the resistance didn't change.
Tried the same with the sensors connected and couldn't replicate the fault.
I have a megger so I could do an IR test core to core, is that a thing on 12v systems? (I'm an electrician by trade)
I'm moving towards being unlucky and having another bad module with the same fault but it just seems very far fetched.
Also, I havent messed with the rear sensors as the code was for the front sensors. Should I be checking the rear anyway?
Great work, I'm thinking that the wires you checked are ok, don't think there's a need for a megger.
Might be a good thing to check the rear too.
Out of curiosity, do *any* of the circuit boards involved have any spots where they're screwed down to provide a ground connection? I've seen problems with those before.
Just a thought, has there been any other work done on the car just before this happened
Yup, it would definitely be weird to have the same problem on 2 boards.
I took the old module apart, the board is just a card that slots into a plastic housing without screws.
It has been this way since I bought the car, ended up getting money knocked off it rather than returning it or leaving it for repair.
The voltage at the sensors is just battery voltage. Does that mean I can take an ignition live from the fuse box and a new ground to the sensor loom on the front bumper.
Im thinking if it is in parallel with the supply from the module then it can't lose voltage and throw up a code?
I do not have hands on time with these actual sensors but I recall they are all wired in a string such that one bad sendor pulls down the whole set.
It can be time consuming to test - See which one respond/not respond to proximity.
Usually water is allowed through the harness connector seals and the sensor is total-loss.
Same harness issue is applicable to radar modules front + back.
Cheap insurance... RTV silicone every exposed connectors you see around the bumpers and engine bay.
I do not have hands on time with these actual sensors but I recall they are all wired in a string such that one bad sendor pulls down the whole set.
It can be time consuming to test - See which one respond/not respond to proximity.
Usually water is allowed through the harness connector seals and the sensor is total-loss.
Same harness issue is applicable to radar modules front + back.
Cheap insurance... RTV silicone every exposed connectors you see around the bumpers and engine bay.
It could be that, but I'm not sure the best way to test as the fault is intermittent.
They are 3 wire sensors, power and ground cables are crimped together in the middle of the harness. Each sensor has its own signal wire.
I could try and short one of the plugs to see if this would bring the same fault code.
Distance readings all show correct in diagnostics.
Remember that these are amazing computers on wheels, not sure if wiring direct will cause harm.
Did you check the DC voltage leads using the AC scale of your multimeter? Dont forget to check the ground lead as well. If your meter has a capture (history) function, maybe do a capture on each lead while driving then review the capture each time in your garage. Need to use some extension test leads, I guess.
the "process of elimination" is very helpful way to troubleshoot.
It will help you figure what unit got soaked AND what connector are oxidized.
You said each sensor on your chassis has its own individual unshared serial data line: then modules are a bit easier to single out for identification.
🤞
CaliBenzDriver is right on target. The process of elimination *is* time consuming, but a necessary thing here. Just out of curiosity, have you found any evidence of water entry or corrosion?
I've noticed that it can take a minute to find faults, I have a headlight fault that I'm going to ask all you good folks about. Takes up to 90 seconds or so to report it on the display.
If I remember rightly, you mentioned some codes, can you clear them?
Any visibility of this in the "secret" engineering display menu (don't make any changes there!).
Thanks I'll focus on a sensor being at fault for now.
If I unplug a sensor and test resistance across + & - pins, should I see a resistance?
I plan on taking out the remaining 2 sensors and testing to see if the resistance is different on them.
The code that gets stored is: B12851C - The front distance sensors have a malfunction. The voltage value is outside the permissable range.
The hardest thing with eliminating the fault is it clears when the car is turned off so I'm still unable to do any testing on the driveway with the fault present.
Just curious, how does the fault show itself? Do you get a message on your dash? If not, can you live without Parktronic? Are there other symptoms you need to worry about?
You said you negotiated a lower price because of the problem versus getting it repaired. I hope what it is now costing is less than the discount you got. Clearly, the seller thought the discount was less than what it would take to repair the problem. There is a good chance that there is a bigger problem and that is why the seller was willing to cut the price to get a problem gone.
Just curious, how does the fault show itself? Do you get a message on your dash? If not, can you live without Parktronic? Are there other symptoms you need to worry about?
You said you negotiated a lower price because of the problem versus getting it repaired. I hope what it is now costing is less than the discount you got. Clearly, the seller thought the discount was less than what it would take to repair the problem. There is a good chance that there is a bigger problem and that is why the seller was willing to cut the price to get a problem gone.
Its a long beep, 4 lights on the sensor bar and it turns off.
To be honest the garage offered to take the car back and repair it but it's 80 miles from me and I just didn't think it was worth it. He agreed to bank transfer some cash to me instead and I'm grateful for that.
I assumed it would just be 1 sensor but when I eventually got round to plugging it in, its lead me down this rabbit hole and now im more curious to find the cause.
Ps its been over a month now (due to my own laziness) so I cant expect anything from the dealer.
Little update:
New front outer sensors arrived, wouldn't work. Both showed component fault codes.
Funnily enough I've only just noticed it throws no codes with the outer sensors unplugged.
New plan:
Leave the outer sensors unplugged. If I don't get the voltage code in a few days I'll know it was those sensors and ill just order new direct from mercedes.
Little update:
New front outer sensors arrived, wouldn't work. Both showed component fault codes.
Funnily enough I've only just noticed it throws no codes with the outer sensors unplugged.
New plan:
Leave the outer sensors unplugged. If I don't get the voltage code in a few days I'll know it was those sensors and ill just order new direct from mercedes.
So you still don't know which sensors are actually bad. We can guess it's not the new ones.
You proved your harness good after inspection...
Where does this circuit leads to: the SAM or a dedicated controller module ?
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