Newbie question about making a CLA "LED friendly"

European GM ECUs and PCMs
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Newbie question about making a CLA "LED friendly"

Postby Mathieu86 » Sat Dec 07, 2019 1:55 am

Hi everyone,

I just have a question that no one seems to be able to answer in a confident way. I would like to install LED tail lights on a Mercedes that came with the basic lights. This is not plug and play, it needs reprogramming.

A shop from China is selling a "reprogrammer", basically it's a small device the plug in the OBD2, it beeps after a few seconds and the car is then "led friendly".

I have only 1 reference of someone that did that and I am quite scared of doing something bad to my car.

Is there a risk of damage to the ECU ? If the programming goes wrong, is it always possible to reset the ECU to how it was before ? I guess the way those devices work is quite similar on bikes and it seems that you guys here know quite some stuff about it.

Thanks in advance for your answer !

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Re: Newbie question about making a CLA "LED friendly"

Postby j_ds_au » Sun Dec 08, 2019 10:50 am

My guess is that this is setting a blown-lamp-detection feature to disabled.

If something goes wrong, it might screw up your settings. Only precaution would be to read/save them first.

That's just a general view of matters, you'd need to dig deeper for the particulars of your ECU.

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Re: Newbie question about making a CLA "LED friendly"

Postby Gampy » Sun Dec 08, 2019 10:24 pm

They make LED replacements that have circuitry in them to fool the ECU, Never tried them on my Mercedes, and wouldn't, I don't put CRAP on my Mercedes. (Chinese Repair Auto Parts)

Where to find them?
There are a gazillion resellers in the cesspool. (Internet)
Do they work on Mercedes, I dunno know, you would have to start contacting some of them gazillion resellers and ask!
Last edited by Gampy on Tue Dec 10, 2019 5:12 am, edited 1 time in total.

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Re: Newbie question about making a CLA "LED friendly"

Postby Mathieu86 » Mon Dec 09, 2019 5:17 pm

Thanks for your answers !

Apparently it's the power needed for LED that is way lower than the one needed for halogen so indeed the system thinks there is a problem with the lights if you just swap them.

Regarding saving the original parameters, how can it be done ? Also, do you think resetting the ECU would make it go back to halogen or those kinds of settings are not affected by the reset ?

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Re: Newbie question about making a CLA "LED friendly"

Postby antus » Mon Dec 09, 2019 5:47 pm

More general info, its probably a setting in the body control module (bcm) not the ecu. Mercs are not the only car to do the blown light detection thing, bulb replacement with the type that are designed to waste power to work with older detection circuits will work.

I think the risk with the chinese tool would be reasonably low, it'd just be a copy of what the factory software does. Anythings possible but itll most likely work or fail without doing damage. There isnt a factory reset, its designed to be a factory only calibration item and the expectation is if it needs to be changed back then you change the setting back with the same tool. Can the chinese one do that? Not sure.

Factory software and interface can probably do it too. Xentry is the name of the factory software.
Have you read the FAQ? For lots of information and links to significant threads see here: viewtopic.php?f=7&t=1396

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Re: Newbie question about making a CLA "LED friendly"

Postby Mathieu86 » Tue Dec 10, 2019 3:19 am

antus wrote:More general info, its probably a setting in the body control module (bcm) not the ecu. Mercs are not the only car to do the blown light detection thing, bulb replacement with the type that are designed to waste power to work with older detection circuits will work.

I think the risk with the chinese tool would be reasonably low, it'd just be a copy of what the factory software does. Anythings possible but itll most likely work or fail without doing damage. There isnt a factory reset, its designed to be a factory only calibration item and the expectation is if it needs to be changed back then you change the setting back with the same tool. Can the chinese one do that? Not sure.

Factory software and interface can probably do it too. Xentry is the name of the factory software.


Amazing ! Thanks a lot for the info ! The Chinese tool only works one way. I am planning to replace the whole housing, not just the bulb. Worst case, do you think it would be feasible for someone with no knowledge about Xentry and ECU related stuff to set it back to halogen ? I am not planning to go back to halogen but if at some point the LED is not working it would be nice to have a way out.

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Re: Newbie question about making a CLA "LED friendly"

Postby antus » Tue Dec 10, 2019 3:40 pm

I think you would not need to set it back. The worst that I'd expect to happen is to loose the blown bulb detection feature.
Have you read the FAQ? For lots of information and links to significant threads see here: viewtopic.php?f=7&t=1396

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