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1996 C220 Auto-tragic
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44 Posts
Discussion Starter #1
Does anyone know if the Diagnostic module can be exchanged without coding it for the car? As I understand the Diagnostic module is only a data collection device used to interface the engine ECU, run the OBD II test and collect the data. I guess also collects chassis, ABS and body codes from other modules.

My OBD II tester indicates the ODBII tests are "not available". So of course will not pass emissions. Also the OBD II machine at the Emissions station reported the same thing. Tried disconnecting the battery for 15 min a couple of times, clears check engine light but doesn't reset the OBD II test section. Weird part is all of the other data it there RPM, load, ignition, air flow, etc. So I know the module is working.

Also there are no Blink codes from the 38pin connection using a LED/switch box. Get a single blink code indicating no codes stored in the ECU.

I don't have Star Diagnostics available to me and am trying to avoid going to dealer $$. As I can buy a used diagnostic module for fairly cheap.

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1996 C220
 

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'99 2.3L Kompressor
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1,944 Posts
Are you sure it isn't just indicating that you have to drive the minimum 100 miles (?) required by the regulations any time the stored codes have been cleared? This is by law to keep people from clearing codes and driving to the emissions station before codes pop back up.
 

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1996 C220 Auto-tragic
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44 Posts
Discussion Starter #3
Yeah tried driving for couple of weeks, same result. This issue is the code scanner indicates the non-continuous OBD II tests are 'not available'. The continuous tests run fine and indicate 'ready'.

Very odd issue. Appears the diagnostic module is not providing the necessary ODB II data bytes to scanner. I know the module is working as the providing live engine data on the scanner.

Thanks
 

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1996 C220 Auto-tragic
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44 Posts
Discussion Starter #4
Got to pass emissions

Replaced the OVP relay and diagnostic module started working and completed most of the non-continuous tests and all continuous tests. Two of the tests were still not complete but passed emissions for a 1996. Strange situation as the Diagnostic module is powered thru the OVP relay but the Dianostic mod had power (verified with DVM) before replacing it. Also I was able to get all the live OBD II data from diagnostic module with old OVP relay. Thought the OVP relay was only for overvoltage? It appears the OVP relay also delays the power to the dianostic module/ABS modules on startup. Also no more ABS light since replaced OVP relay.

Anyway thought info might be useful for someone else with a 96 C220/C280. It seems the diagnostic module software for this year is not well written and had some bugs. Like turning on the MIL light anytime the OBD II is used. Had to explain to the Emissions tech about this SW bug.
 

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1997 E420 149,000, 1996 C220 114,000, 1996 Porsche 928S (sold), 1980 300D (Dead)
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10 Posts
I replaced my OVP and have driven 110 miles so far and still have 6 incomplete tests. I know that may not be enough miles driven yet but am looking for anything else that might get those tests to complete.

I know - I have read the posts that indicate it is all about the type of driving and I have been following some of the drive cycles that I have seen posted but so far... I still have six incomplete tests and I need to get those down to 2 incomplete (here in the Democratic People's Republic of California) so until I am still driving it to get it to go. I am considering changing my Diagnostic Module and would like to hear if anyone else has had that experience.
 

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1996 C220 Auto-tragic
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44 Posts
Discussion Starter #6
Like you comment about the 'Democratic People's Republic of California' par for the course. At times wonder if CA part of the USSR, although don't live there now spent a lot of time there.

Did you try and disconnect your battery? I think this is a only way to reset the diagnostic module, then you have to start the drive cycle again, but for me only thing that finally worked to reset. Make sure you have your radio code. Also I did an ECM reset procedure, not sure if this helped.

Do you have an OBD II tester? If so check that you are getting live data this will tell you if module working.

Yeah I spent a couple of weeks of nights in the garage working on this stuff. The SW on this module sucks. I also thought about replacing with a module from like a 97' or later car but no one could answer if the module needed to be coded for the ECM.
 
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