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Bosch LSU 4.9 Troubleshooting 
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TO92 - Vaguely active

Joined: Thu Mar 20, 2014 6:33 am
Posts: 1
I have been experimenting with a Bosch LSU 4.9 wide-band sensor. It doesn't seem to be working. I'm curious if anybody could tell me a way to troubleshoot the thing. I have measured resistance on all signal pins. I measure about 3 ohms (at room temperature) across the heater pins. I measure about 100 ohms across the trim resistor. However, I measure opens across both the nernst cell and the reference cell. This makes me think I might have a problem. I am using the sensor with a bosch cj125 IC. After setting the thing up, it seems that the resistance output that reports the resistance of the nernst cell never changes, and the actual lambda value is always 1.5 V. I am suspecting the LSU 4.9 itself. Any suggestions?


Thu Mar 20, 2014 6:42 am
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Wideband Wizard

Joined: Tue Jun 10, 2008 2:53 am
Posts: 241
Location: Toronto Canada
makin_mistakes wrote:
I have been experimenting with a Bosch LSU 4.9 wide-band sensor. It doesn't seem to be working. I'm curious if anybody could tell me a way to troubleshoot the thing. I have measured resistance on all signal pins. I measure about 3 ohms (at room temperature) across the heater pins. I measure about 100 ohms across the trim resistor. However, I measure opens across both the nernst cell and the reference cell. This makes me think I might have a problem. I am using the sensor with a bosch cj125 IC. After setting the thing up, it seems that the resistance output that reports the resistance of the nernst cell never changes, and the actual lambda value is always 1.5 V. I am suspecting the LSU 4.9 itself. Any suggestions?


All your resistance measurements are correct. If the resistance is not changing it is probably because the sensor is not being heated. I believe the bosch chips require you to use another micro to read the resistance from the bosch chip, and then drive a FET to heat the sensor. No Idea why the Bosch IC does not drive the FET itself.

Alternatively, you can use my SLC Free open source design. It is a single chip design, all you need is the micro + about the same number of passives + a FET (which you also need for the Bosch IC). The sensor is controlled with a single micro and that includes controlling the heater, so parts wise it is a lower part count than the Bosch ICs and much easier to work with. I have tested 3 brands of controllers that use the Bosch IC, and they were all dissapointing in terms of accuracy when I benched them using my calibration gas. So I am going to go out on a limb and say that the SLC Free Design is much more accurate than the Bosch ICs.

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Thu Apr 10, 2014 7:40 am
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