Fixing cheap ebay USB KKL cables

Bosch Motronic etc ECUs and PCMs
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Fixing cheap ebay USB KKL cables

Postby festy » Tue Jul 16, 2013 4:55 pm

To use a cheap POS ebay USB-KKL interface with the older Motronic ECUs they need a slight modification to work reliably.
The KKL interface uses two lines, a 'K' half duplex line, and a 'L' low speed init line.
It's very similar to an ALDL one wire interface, the K line is used for both tx and rx. The L line is simplex and only used to "wake up" the ECU by sending a 5 baud ID byte (yes 5 baud, i.e. 2 seconds per byte!) then it's not used any further.

The cheapest KKL cables use a WinChipHead CH340T USB-serial bridge, which is quite decent - but for some reason the interfaces are designed with the K and L lines effectively tied together which makes the connection very unstable.

The fix is to separate the L line, and connect it to the CH340T chip's RTS pin so it can be driven independently of the K line:
KKL_mod.jpg (238.29 KiB) Viewed 2762 times

And here's a schematic I traced out for the un-modified interface, you can see that the K and L lines are tied together:
KKL_CH340.jpg (35.88 KiB) Viewed 2762 times

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Re: Fixing cheap ebay USB KKL cables

Postby Besiseitaj » Wed Feb 27, 2019 7:08 am

Will this modification work on this cheap usb kkl cable?

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Re: Fixing cheap ebay USB KKL cables

Postby antus » Wed Feb 27, 2019 12:22 pm

It looks like the same design down to the same component numbering in the same place. I think it would work.
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