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My power rear liftgate opens fine, but will no longer power-down. It just ignores all button presses. I've power-cycled the rear SAM, pulled fuses, and tried the big button on the rear door, driver's control and the remote. All of them just ignore the close command.
Reading codes with my icarsoft, I see these errors:
Component B86/2 (Right rear-end door closing obstruction sensor strip) sticks in the switched state (contact sticking)
Plus the same message for the other side (B86/1).
My searches of the car and the web have not turned up these sensor strips, or their locations. Has anyone found them and replaced them?
I found the sensor on the R350, it was well hidden. It's built in to a trim piece along the vertical edges, that goes from up around the hydraulics down the vertical. The sensor strip is along the edge, and stops as the tail light assembly. I was able to open the rear access panels and find the wire (two wire, with red connectors) and verify that the icarsoft detects it as "missing" when I disconnect it, and "triggered" when it is plugged in. Resistance is about zero ohms, so it looks to be shorted.
Part number is A2516900730 D-Pillar cover V/W251 with APS for the left one. Found one on ebay, may give it a try but I think I'll call the dealer first. If that price is similar to the above, I may just go new (if it is still available).
I did not try it, but I'd think it would not power down with a missing sensor. I could figure out the resistance of the good one and patch in a resistor, but wouldn't want to disable a safety device.
I did not try it, but I'd think it would not power down with a missing sensor. I could figure out the resistance of the good one and patch in a resistor, but wouldn't want to disable a safety device.
You can test to see if the switch is sticking by removing the rear tail lamp cover inside the trunk space and separating the connector (dark red connector with two wires [green and a yellow w. stripe]) and insert a 3.9 kOhm (orange white red gold [5%]) resistor, for the left, or a 2 kOhm thermistor, for the right, as in the picture. The tailgate close or remote will now work if the sensor was the problem. I cut off the connector and permanently attached a 2 kOhm thermistor (right side) and sealed it with adhesive lined heat shrink. I then had to manually clear the DTC code and everything works (except no pinch obstruction which I have never needed in the 14 years that I have owned the vehicle).
You can see the part number on the sensor lead i.e. on my 2008 ML320 CDI it is A1648600118 for the left and A1648600218 for the right. The Mecedes dealership denied that these part numbers even exist (even after I showed them pictures). Occasionally, used parts show up on eBay. Sensor replaced with 3.9kOhm resistor
Last edited by dwwaddell; Aug 19, 2021 at 03:52 PM.
Reason: Correct URL and add notes
Thank you just fixed my rear gate that did not want to close! 100 resistors for $6.30
straight forward fix, open side covers, unplug sensors, connect resistors on both sides, tape them so it holds resistors connected and isolated.
Done.
5 minute, $.0.12 cent repair.
Sorry to be late to the party! My R tailgate won't come down unless by hand. Both pinch sensors read 3.9K. I think this is the default, having one side a different value seems incorrect to me. We use bump strips at work and they should read either the end of line resistor value or near short circuit when pinched.
They can read other resistances if twisted or damaged.
So how does one get to the red button? That seems an obvious suspect.
The button simply pulls out without too much effort. There is a 390R end of line resistor in it and a couple of LEDs. The switch itself works fine. I'm told the position feedback potentiometer was changed (I can se missing trim clips around it) so I'm not entriely sure what is left without finding the control unit and testing signals there. Must get a Merc specific OBD tool!
Last edited by dogshome; Aug 31, 2023 at 07:37 AM.
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