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OBD2 Issues

Tiny
BLACKNACOUSTIC
  • MEMBER
  • 2003 MERCEDES BENZ C320
  • 3.2L
  • V6
  • 2WD
  • AUTOMATIC
  • 200,000 MILES
Having issues with the car listed above I bought.

I took it to a shop to get it repaired and they couldn't check to see anything because the OBD2 sensor wouldn't power on. I was having this issue before so I previously checked all the spark plugs and all of them looked okay, no issues found. What should my next steps be?

Also, does anyone have a copy of the wiring diagram for the car?
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Wednesday, December 4th, 2019 AT 9:52 AM

15 Replies

Tiny
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I am not sure I understand. You are saying the issue is the scan tool cannot communicate with the vehicle and you checked the spark plugs? The spark plugs would not cause this issue. You have a wiring issue or a module issue. Do you know if there are able to communicate with any module? If not, I suspect the DLC (connector under the dash) is the issue.
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Wednesday, December 4th, 2019 AT 4:16 PM
Tiny
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How would I confirm that I can communicate with the module? And what should I be checking to go about fixing this issue?
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Wednesday, December 4th, 2019 AT 4:54 PM
Tiny
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You need to unhook the connector from the ECM and then measure resistance from the DLC to the ECM on that circuit. If there is less than a half ohm of resistance then the wire is intact. After that, the actual connector terminals could be an issue. If not then the ECM is the issue.

This is all assuming the scan tool was capable of communicating with this vehicle. Clearly I cannot answer this question because I don't know what tool they used or the protocol it operates on.
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Wednesday, December 4th, 2019 AT 6:16 PM
Tiny
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I've tried 4 different scan tools of different kinds, so i'm sure your on to the right track. I'm going to try that this weekend and let you know how it goes.
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Wednesday, December 4th, 2019 AT 6:25 PM
Tiny
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Sounds great and it sounds like you eliminated the scan tool as the issue. Thanks and I will wait to hear back. Thanks
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Wednesday, December 4th, 2019 AT 6:32 PM
Tiny
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Okay status update.

So we pulled out the entire ECU to check it, had two bent pins that we fixed back and checked the OBD2 sensor again with no results.

We then checked the continuity of the OBD2 pins. 7 and 8 had 12 volts, but 16 did not. We then checked the Ohms and Continuity from the port (16) to the wire that plugs into the ECM and got OL on the meter and no continuity. Car is still in limp mode.

A couple of questions

1. 16 is showing Red/Green cable. Does that go to one of the connectors directly connected to the ECU or does it run to a fuse/something else in the fuse box under the hood.

2. With the issue possibly being that wire, what should be our next steps to correct this issue?
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Sunday, December 8th, 2019 AT 3:01 PM
Tiny
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If you look at the diagram, pin 16 of the DLC goes directly to the Front SAM module. So you need to test resistance/continuity from the DLC to the SAM module pin 11.

If you have an issue here then clearly that needs to be fixed but I suspect those bent pins may still be an issue. Usually when they bend they are difficult to fix. It may be worth while to recheck them to make sure they didn't bend again.
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Sunday, December 8th, 2019 AT 7:14 PM
Tiny
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So I noticed that there is not a relay where the number 7 is. Is that an issue?

Also, how do I test the Sam module? Can I pull the entire thing out and test it or is there a specific way to get to that pin?
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Monday, December 9th, 2019 AT 3:50 PM
Tiny
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I am not sure I follow with what number 7 you are talking about. If there is a label for the relay meaning it is not a blank space but says it controls something then it does need to have a relay in it.

As for the SAM module you just want to unhook the connector and measure resistance from the DLC to that connector on the same wire.
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Tuesday, December 10th, 2019 AT 5:00 PM
Tiny
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Okay, I don't want to sound extremely ignorant, but i'm very confused about the specific location of pin 11 and how to get to it. And on the picture below where the 7 and 8 is written on the relay, there is a relay where 8 is but no relay where 7 is. Is there a diagram or schematic that you could send me with the information of what relays/fuses should be there and what they control.
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Wednesday, December 11th, 2019 AT 5:19 AM
Tiny
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Here are some pictures of what my SAMS module looks like to get you an idea of what im looking at.
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Thursday, December 12th, 2019 AT 5:42 AM
Tiny
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Additionally something I noticed over this week, the battery has been dying slowly when its not started in a days time. I've had to jump start it if I don't work on it the next day and work on it the day after.
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Thursday, December 12th, 2019 AT 9:18 AM
Tiny
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Okay. I would get a relay and put in there. It does look like there are metal tangs in the cavities which means it is not an empty cavity. As for the battery draining, that would not be related so we will need to figure this out and then start a new post on finding the possible cause of the drain.
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Thursday, December 12th, 2019 AT 5:24 PM
Tiny
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Okay, im still having trouble finding pin 11. Could you possibly offer some more information to help me find it?
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Friday, December 13th, 2019 AT 8:03 AM
Tiny
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So the OEM diagram showed the pin 11 on the SAM module but the AllData wiring diagram shows the DLC goes to pin 19, 20 and 24 or the SAM module C6 connector. At this point, I don't know which one to trust however, since you are having an issue finding pin 11 maybe the OEM one is wrong.
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Sunday, December 15th, 2019 AT 1:55 PM

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