Mercedes SL 500 R230 - No central locking plus vario roof fault

Adam Owner/Technician Glasgow, United Kingdom Posted   Latest  
Question
Electrical
Network Communications
No Central Locking From Key
Vario Roof Inoperative

Gents,

I hope this finds you all well. I wonder if someone can shine some light...

Make/Model: Mercedes-Benz/SL500

Engine: 5.0 L

Fuel: Petrol

Year: 2003

BHP: 310

Engine Code: 113963

VIN: WDB2304752F049886

Central locking doesn't work via key and convertible roof wont operate. Found via scan-data that the overhead control panel control unit (OCP, N70) module has NO COMMs and isn't showing up in the scan. The only other related faults across other modules are just the reports that N70 cannot be seen. 

The N70 module is responsible for reading in the roof closed limit switch position and also receives the key signal for the central locking. So I need to get this module back up and I'm pretty certain that, when I do, things will be sorted. 

So far, I've checked/confirmed the following:

  • Power to N70 module good (checked at module)
  • Ground to N70 module good (checked at module)
  • N70's CAN wires to network distributor connector are good
  • Forced actuation of central locking works fine (actuated via different module)

At this point I thought it likely that the N70 overhead control panel control unit was faulty and got a 2nd hand unit from eBay. Alas, no further forward - same faults and N70 still isn't able to be accessed with scan tool. Unless I've been extremely unlucky with this supposedly "fully working" used N70, something else is going on here. These cars have serious issues with water ingress but this car is an exception - every area usually associated with problems from water ingress is bone dry. Something that's making me doubt the replacement N70 is that the integrated interior lights still don't work...Surely these would work fine even if the network had issues as power/ground to the N70 is 100% confirmed good?

Can anyone shed any light? Would be most grateful for any input.

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Igor Owner/Technician
Glenview, Illinois
Igor Default
 

Hello, have you checked PSE pump in the trunk under vario roof pump for water damaged ?

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Raymond Diagnostician
Phoenix, Arizona
Raymond Default
 

I agree with Igor, have seen many with water intrusion in the trunk

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Adam Owner/Technician
Glasgow, United Kingdom
Adam Default
 

Yes. As mentioned, bone dry.

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Bill Owner/Technician
Jackson, Michigan
Bill Default
 

I know you say you have checked the PSE for water intrusion but have you verified it's proper function? I have seen similar issues with failed PSE pump/module.

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Adam Owner/Technician
Glasgow, United Kingdom
Adam Default
 

Yes. As mentioned, forced actuation via PSE was confirmed in early testing.

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Caleb Diagnostician
Mishawaka, Indiana
Caleb Default
 

I am not in front of a schematic so just shooting a quick response from the hip. Did you check the CAN lines dynamically with connector connected to N70? Is it possible that N70's ability to communicate is being pulled down by a component, sensor or wire etc that is connected to N70? Thats were I would go. Look for any ref voltage circuits that N70 outputs. See of something is shorted.

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Adam Owner/Technician
Glasgow, United Kingdom
Adam Default
 

Many thanks. I’ll electrically remove and eliminate components from N70 and see if comms come alive. I guess I should monitor CAN H&L via oscilloscope too. Would you mind detailing your “dynamic testing” process?

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Caleb Diagnostician
Mishawaka, Indiana
Caleb Default
 

Dynamic just means test the circuit or circuits in there normal operating mode. As in everything connected, backprobing or piercing, car running etc. Static is opposite. Car off. Unplug component "X" and check for 12 v etc. I try to avoid static testing as much as possible.

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Adam Owner/Technician
Glasgow, United Kingdom
Adam Default
 

Ah yes, thank you. I call that "under load", perhaps incorrectly.

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Caleb Diagnostician
Mishawaka, Indiana
Caleb Default
 

Yep you got it. Basically same idea!!

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Caleb Diagnostician
Mishawaka, Indiana
Caleb Default
 

Did you come up with anything Adam??

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Adam Owner/Technician
Glasgow, United Kingdom
Adam Default
 

Hi Caleb, Will know Monday/Tuesday. Wikl keep you posted 👍🏻

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Caleb Diagnostician
Mishawaka, Indiana
Caleb Default
 

Cool not policing ,just curious 👍😉

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Adam Owner/Technician
Glasgow, United Kingdom
Adam Default
 

Hi Caleb, I've now completed the additional testing. Results as follows: - Powered up N70 on bench: NOT WORKING - NO SIGNS OF LIFE - Powered up known-good N70 from CL500 on bench (slightly different part but same era and configuration): ON-BOARD LIGHTS WORK VIA SWITCHES AS EXPECTED - Checked CAN signals at N70 with KEY ON: Look good (still need to verify against spec) - Checked CAN…

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Bill Owner/Technician
Jackson, Michigan
Bill Default
 

Adam I believe your CAN B voltages to be correct, I have also attached a great MB Communication Document for future reference. Looks like you may have a failed N70 at this point.

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Adam Owner/Technician
Glasgow, United Kingdom
Adam Default
 

Great doc - many thanks for sharing, really appreciate it!

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Raymond Diagnostician
Phoenix, Arizona
Raymond Default
 

Are you using a factory scanner? any codes stored?

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Adam Owner/Technician
Glasgow, United Kingdom
Adam Default
 

Yes. OEM all the way.

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Adam Owner/Technician
Glasgow, United Kingdom
Adam Delay
 

UPDATE: Done a bunch more testing all still points to defective replacement N70 - 2nd replacement now on order. Will post further update following install early next week.

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Adam Owner/Technician
Glasgow, United Kingdom
Adam Resolution
 

FIXED: As suspected, the first replacement N70 was defective. 2nd one fixed it. This one hammered home the risks with eBay etc. Silver lining: Hopefully this may be of some help to anyone in the same situation.

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