Test and Measurement Forum

I have a problem. ECU report P0420-007 Catalyst efficiency below threshold. Measure both lambda (before and after the catalytic converter). Both have a sample course. Just probe the catalyst is different in that it has some kind of regular or needle tip. The first image that I attach is a sample graph and the second image shows the tip of the lambda probe diagnosis. Please what causes these peaks and this course ? Thanks for the info.

Hi Mirda

Sorry but I don't understand the question.

Regards

Dave Hill

Mirda,

First of all, it seems this is automotive specific, so this particular forum is probably incorrectly placed.

Secondly, it would be helpful if you would put the year, make, and model in your post.

I agree with Mr. Hill. I'm not understanding the question either. What is the course you are referring to? Is the "needle" you are referring to the spike at the beginning of the traces? If so, I wouldn't worry about it. That is just probably noise.

I would caution you to use scope traces to determine if a catalyst is doing its job. You can have pre and post catalyst lambda sensors that appear to be mirroring each other and the catalyst is just fine. Trust the ECU to make that determination.

If you know the lambda sensors are active, you have checked for any TSBs for a reflash, and there are no exhaust leaks, then the only thing left is a new catalyst. You should be very careful if you choose to use an aftermarket catalyst. Their emission reduction efficiency will not be as good as OEM.

Hi Dave/Carl

same here ??

Rob.

Let me try to clarify. My measurements show the same process as black and white picture. Just do not know what causes the periodic voltage spikes (same as in the figure).That is, if the measurement results are the same as the proper charts, so why not come this disorder(P0420-007)?The color sample chart the course of the diagnostic probe, which operates such a good linear without voltage peaks. Now I do not know what is right.

I think I understand the question (eventually)

Looking at the examples that you posted & taking your comments on board, I think you are confusing the traces. Your example with "the peaks" is displaying the heater circuit & not the oxygen sensor signal.

The other "four channel colour" waveform, shows the signal output from all four Oxygen sensors on a V8 configuration.