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P0422 CEL - Main Catalyst Efficiency Below Threshold (Bank 1) - My thoughts...
My 2007 GL450 is throwing two CEL error codes:
P0410: Secondary Air Injection System
P0422: Main Catalyst Efficiency Below Threshold (Bank 1)
I think I have the P0410 one addressed, but the second one, P0422 showed up. Now, it could be that it has been there for quite a while, because I just bought this truck and know that the catalyst cycles can take some time to show up if the seller had the battery disconnected (which I suspect is the case). Truck has 197K miles on it. Yep. That's a lot. But other than these, one front strut airbag (which I will replace with an Arnott), and a weak rear lift hatch hydraulic, it's in great shape and worth keeping up.
So, back to the P0422 code... Truck runs well. No secondary issues. Engine is smooth. When I connect my OBD2 scanner and Torque to it and watch the catalytic converter and O2 sensors, it shows that it's barely below the threshold for triggering the CEL (see screenshot). I'm not sure if that reading leans towards the cat being on its way out, or that one of the O2 sensors needs to be cleaned or replaced - or if it's just a red herring. I can't just swap the O2 sensors and see if the error follows the sensors to Bank 2 or sticks with Bank 1 because the O2 sensor cables are different lengths. Anyone have any thoughts on troubleshooting this one?
Last edited by jtb33; Aug 30, 2018 at 05:31 PM.
Reason: Clarification
So, that's passenger side, the one that's right on the Catalytic Converter towards the rear of the vehicle (and easiest to get to)? (ie, Bank 1, Sensor 2)
the problem with your post cat o2 is it sees too much oxygen or o2 zig zags leading to the code for bad cat. spacing the sensor will not change that. you need a sim - it is a dummy o2 sensor that always shows "good" signal
I think the idea with the spacer is that it averages out the exhaust mixture, so if the dying cat is being overwhelmed by the CO and HC in the exhaust, it doesn't have spikes that trigger the signal.
For everyone's education:
The post-cat sensor is an on-off device; if the oxygen levels in the exhaust are above a certain point, it sends a signal. No signal = cat ok. Signal = cat not ok. Or the other way around; I don't know.
The pre-cat sensor is a "wideband" device, meaning it gives a range of signals regarding the oxygen level in the exhaust. The engine computer uses the pre-cat sensor to adjust the fuel mixture.
The post-cat sensors are easy to get to and replace, relatively speaking. They do go bad, but unfortunately they do so on about the same schedule as the cats, as alx pointed out. You might get a few more miles out of your cats by replacing the post cat oxy sensors. If you have a reasonable mechanic, he won't mind keeping the old-new oxy sensors when you change cats, so it's a relatively cheap trial fix. With the proper tool - I took a 22mm box end wrench and cut a slot in the end with an angle grinder and cutting disc - and a propane torch to heat the bung nut, they aren't too hard to remove. Biggest problem is waiting for the sensor to cool so you can remove it by hand.
The box end wrench, with the cut-open end, makes a nifty little tuning fork.
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P0422 CEL - Main Catalyst Efficiency Below Threshold (Bank 1) - My thoughts...
