Quick oxygen (lambda) sensor question

**omglol** · 22nd January, 2011, 10:57 PM

Hello!

I just wanted to how should oscilogram of oxygen sensor 2 (the one AFTER the CAT) work? Same as sensor 1 or not?

Here I have picture from Citroen C2 VTS, make year 2006.

Red one seems OK to me, but blue one isn't OK, am i right?

**Liteace** · 23rd January, 2011, 03:59 AM

Looks all Ok, any fault codes or drivability problems. The downstream lambda main job is to monitor the efficiency of the cat, when the cat is good and doing it job you should not see anything more than about .??v and with hardly any fluctuations in the scope reading, dont forget the downstream lambda is sensing cleaner pollutants, if you see more activity when scoping downstream lambda your cat is on it way out

**cars** · 23rd January, 2011, 08:18 AM

Originally Posted by omglol

Hello!

I just wanted to how should oscilogram of oxygen sensor 2 (the one AFTER the CAT) work? Same as sensor 1 or not?

Here I have picture from Citroen C2 VTS, make year 2006.

Red one seems OK to me, but blue one isn't OK, am i right?

In my opinion the red (if the upstream oxygen sensor) is correct, while the blue signal no. The second sensor, says Liteace, serves to monitor the signal, and if it works to combine all the oxygen in the gas (O + CO = CO2) and then in the absence of oxygen the cat of the oxygen sensor 2 must be 0.7V - 0.8 V, fairly constant. observing your signal, or the cat is not temperature or if the sensor is broken.
To test if the sensor is ok, the engine is hot, try different if the acceleration, if the sensor 2 rises to 0.8V and then quickly drops to 0.1V it works correctly.

**soundnavigator** · 23rd January, 2011, 09:13 AM

I think that all is OK. I attach screen copy from Bosch "ME 7.4.4. Operating Principle" to see that.

Best regards.

**cars** · 23rd January, 2011, 12:30 PM

Originally Posted by soundnavigator

I think that all is OK. I attach screen copy from Bosch "ME 7.4.4. Operating Principle" to see that.

Best regards.

Sorry man, but the chart shows that you have posted the correct signal of sensor 2 must be 0.7 V - 0.8 V, rather than that indicated by @omg is 0.28 V, I think I have broken oxygen sensor two or it is cold.

**oldford** · 23rd January, 2011, 10:42 AM

2nd Oxygen sensor produces a signal that is way too low.
I have seen catalysts from Citroen where the mounting of the Oxygen sensor has cracks and leaks air into the exhaust.
This explains it well: http://www.tegger.com/hondafaq/p0420/B971100.pdf