Rear SAM, "input to Circuit 54, short to positive"? - Mercedes-Benz Forum
 
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post #1 of 6 (permalink) Old 05-22-2019, 02:53 PM Thread Starter
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Rear SAM, "input to Circuit 54, short to positive"?

I've got a 2008 ML320 CDI I'm troubleshooting here. The brake lights are staying on all the time when the engine is running, no matter what gear I'm in or weather I'm driving or not. The right turn signal was occasionally flickering rapidly as though a bulb was out too, but they are all tested in good working order. And as I got home, the headlights started flashing as if the alarm was triggered (no siren.)

Scanning all the control modules, the only relevant code showing up, is code 909A in the rear SAM, "the input to circuit 54 has short circuit to positive." It is current and stored.

Any idea what could be causing this? I'm fearing a malfunctioning Rear SAM, I see no signs of
obvious water intrusion .

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post #2 of 6 (permalink) Old 05-22-2019, 04:20 PM
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I know you are using DAS. Click on the code then Test. It should take you to test program for that code.

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post #3 of 6 (permalink) Old 05-23-2019, 04:51 AM
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Quote:
Originally Posted by Rossafuss View Post

Any idea what could be causing this? I'm fearing a malfunctioning Rear SAM, I see no signs of
obvious water intrusion .
You have to go the extra yard and remove everything in the spare tire area including the gray mat to check for water intrusion and inspect the rear SAM which sits on the floor.
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File Type: pdf R&I Spare Tire Well Panel #1.pdf (98.1 KB, 8 views)
File Type: pdf R&I Spare Tire Well Panel #2.pdf (71.1 KB, 6 views)
File Type: pdf R&I Spare Tire Well Panel #3.pdf (82.6 KB, 7 views)
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post #4 of 6 (permalink) Old 05-23-2019, 05:55 AM Thread Starter
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Typically circuit boards dont short to POSITIVE, so due to the water intrusion problem these vehicles are known for near the rear sam, my thought was that water on the circuit board is causing the short between circuits.

So i took the rear SAM out last night to inspect for water, and sure enough, the rear SAM was WET, water all around sitting in the bottom of that well. i removed the board, cleaned the whole thing with electrical parts cleaner and a soft bristle brush, and dried it at 120f in the oven. cleaned the whole area out where the SAM sits, and put everything back together. Problem solved! No DTC's in the rear sam anymore. There was what looked like corrosion all over the board, but given how easily it cleaned off, i think it was actually mineral scale left behind from water intrusion. the board cleaned up very nicely.

trying to find where the water was getting in, im completely stumped. the tail light seal when removed was forming a perfect seal, and the sealing surface was dry and spotless. there WAS however water INSIDE the right side tail light. no visible signs of cracks or broken seals on the tail light housing, so i'm not quite sure where the water is coming in.

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91 300D
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post #5 of 6 (permalink) Old 05-23-2019, 06:01 AM
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Sounds like it's time for new tail light and seal of course.

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post #6 of 6 (permalink) Old 05-23-2019, 10:17 AM
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Get the seals as soon a possible or else the next time it rains you will have new problems.

This time attach the seals to the body opening and not on the tail lamp.
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