Strange behaviour by reading Ur in calibration mode...

Support forum for the Lambda Shield designed to connect Bosch LSU 4.9 wideband oxygen sensors to Arduino projects.
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Joined: 25 Sep 2020 14:27

Strange behaviour by reading Ur in calibration mode...

Post by HeinrichG » 14 Sep 2022 13:40

Hi guys,

my colleagues and I have built a board with a microcontroller (Atmega32M1) and a CJ125. It is an open source project, can be found here: I have the hardware revision v0.0.0 schematic is here: ... a_bl49.pdf

Everything seems to work as well. BUT: I can't get it to read Ur in calibration mode. That is:
1. i send 0x569D to the CJ125
2. i get 0x2800 as answer (i would have expected a 0x289D here?). That means the communication with the CJ125 is error free, but the register is completely at 0x00? That can't be actually?
3. reading Ur now I get 1004 (0x03EC) and this is completely wrong, it is almost 5v (4,9 to be exact). When I measure the pin with a multimeter, I measure the 4.9v....
4. reading Ua gives ADC 308 (1,5v)

Otherwise everything works, I can read the signature, diagnostic register, ... everything okay. If I set Ur calibration to 200, everything works too, Lambda is calculated correctly, O2 is at 20%....

The probe is a brand new original genuine Bosch 0 280 017 025.

Do you have any ideas what else I could try?

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Joined: 07 Mar 2015 18:09

Re: Strange behaviour by reading Ur in calibration mode...

Post by Christian_Bylund » 14 Sep 2022 13:51

Hello Heinrich, we only give support to our products on this website.
Best Regards,
Christian Bylund
Bylund Automotive AB