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ECU no connection

Tiny
HOWEM85
  • MEMBER
  • 2001 MERCEDES BENZ CLK320
  • 3.2L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 100 MILES
Hi, battery went flat new one fitted now roof will not open. I have had this fault several times, normally use Autel scanner clears loads of faults roof and boot open okay. This time scan with obd same Autel tool runs trough to 100% then says no communication.

tried with star through big round plug similar problem.
any help please. Mike

Car listed above is a CLK Cabriolet.
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Tuesday, June 1st, 2021 AT 1:23 PM

11 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

This could be a few things. We need to start at the data link connector to confirm grounds and power supplies.

If you take a look at the pics below, it shows the DLC and where and what to check for. Do this and let me know the results.

Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-check-wiring

Let me know what you find.

Take care,

Joe

See pic below.
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Wednesday, June 2nd, 2021 AT 5:12 PM
Tiny
HOWEM85
  • MEMBER
  • 7 POSTS
Hi, I have 2 pairs of 12v on the obd plug.
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Monday, June 7th, 2021 AT 1:23 PM
Tiny
HOWEM85
  • MEMBER
  • 7 POSTS
Only 4 wires in there 4-5 neg 7-16 +.
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Monday, June 7th, 2021 AT 1:25 PM
Tiny
HOWEM85
  • MEMBER
  • 7 POSTS
Tried to upload pictures off phone but it doesn't seem to work. Thanks for your help.
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Monday, June 7th, 2021 AT 1:28 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

The connections sound good. It did provide 12v, correct?

I attached the entire powertrain management schematic below so you have it as a reference. Today, I need you to focus on the first and second pic below. I highlighted a wire which powers the ECM. I need you to check to see if there is 12v at the ECM.

Also, I'm not familiar with the scan tool you have. Is it able to communicate with other modules?

Let me know.

Take care,

Joe

See pics below.
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Tuesday, June 8th, 2021 AT 7:52 PM
Tiny
HOWEM85
  • MEMBER
  • 7 POSTS
Hi, I am using star mercedes scanner plugged into big round socket into bonnet ECM unit? Where is the location please?
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Wednesday, June 9th, 2021 AT 2:35 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

The ECM is under the hood on the right side near the firewall. I had the chance to speak with a friend today that owns a Mercedes repair shop. I remembered your vehicle and discusses it with him.

What he told me was to do what I suggested first. If you look at the schematic above, it shows the power supply to the ECM. He then added that it isn't uncommon for the fuses to get water to them and corrode causing low or no voltage to the ECM.

I checked all through my manual and was unable to locate the fuse location. He felt it would be in the vehicle on the left end of the instrument panel, so check that as well. Wiggle the fuses when testing for power. Basically, position the test light so you can see it. Watch to see if it flickers.

Another common issue he mentioned is the EIS (electronic ignition switch module). Apparently, these are known problems.

Let me know what you find. Also, let me know if this has a push button or key to start it. That can make a difference as well.

Take care,

Joe
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Wednesday, June 9th, 2021 AT 8:12 PM
Tiny
HOWEM85
  • MEMBER
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If I'm on the correct red, white cable it has no power unclear what fuse it's powered from. Having a look for diagram today on star dia. Thanks
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Wednesday, June 9th, 2021 AT 11:42 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
That is where I'm running into trouble as well. If you look at the pic below, that is the wire that supplies power. It shows the power module/fuse box but doesn't identify a fuse or source.

Let me know what you find.

Joe
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Thursday, June 10th, 2021 AT 7:45 PM
Tiny
HOWEM85
  • MEMBER
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Hi, I believe there was a bad connection at the ECU cleaned it seems okay now. Thanks
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Sunday, June 20th, 2021 AT 11:34 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Thanks for the update. It's appreciated. I'm glad to hear it's running properly.

Let me know if anything changes. Also, please feel free to come back anytime in the future if you have questions.

Take care,

Joe
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Monday, June 21st, 2021 AT 5:55 PM

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