Honcho

CEL today... OBD codes P0036 and P0056

P0036 and P0056 are both downstream sensors correct?
(OBD points to Bank 1 Sensor 2 and Bank 2 Sensor 2)

According to https://mbworld.org/forums/c-class-w...7-request.html

P0036 - Heating of component G3/6 (Right O2 sensor, after TWC [KAT]) : Open circuit
P0056 - Heating of component G3/5 (Left O2 sensor, after TWC [KAT]) : Open circuit

...so part number A0015409517 for the post cat ones is what I think needs to be replaced.

Anything "fishy" about both going out at the same time? Is there a fuse specific to them that I should check first, or anything else to check before hunting down the parts and replacing them?

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boardboy330

It's more likely something causing the car to run rich hence throwing those codes. I would clean the MAF and see how the car runs after. If it's smoother and the codes don't come back - replace the MAF sensor.

Honcho

I've cleared the codes a few times now, and what I'm seeing so far is that on a cold start, it will throw the codes after a few minutes. P0036 & P0056 CONFIRMED, and P0036 & P0056 PENDING

If I clear the codes after a short drive, no more code throwing until the engine sits for a while.

Almost as if the heating elements really aren't getting up to temp fast enough, but I'm still not believing that two sensors went kaplooey at the same time, so still collecting info.

Can't wait til I have my own DAS Xentry!!!

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boardboy330

It really sounds like something else is throwing the codes. I am not sure about this model, but CPS caused issues in other models. Your engine is running rich until it gets to temp. Did you attempt to clean the MAF? It's $5 for a can of cleaner and 5 minutes time.

Honcho

So it's not the cold start that triggers the CEL, it trips after the second start after reset.

I did do the MAF cleaning this weekend, and reset the codes. Stopped at the car wash this morning and shut the engine off while it was getting washed, and a minute or so after starting the engine the CEL is back. Haven't checked codes yet, but pretty sure they'll be the same.

I did find a little mouse nest when checking the air filers/cleaning the MAF, so maybe the little buggers chewed something that goes back to the downstream sensors? I HATE mice!!!!

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Honcho

Mouse Attack!

Just heard from my indy... he found chewed wires... on both sensors.

How I hate mice!

I'm paying an extra fifty bucks per sensor over what I can get them for, but that's the dealio ya get when ya don't want to crawl under the car and do it yourself.

cetialpha5

Can't you just repair the wires? In most cars, the downstream sensors just tell you that the cats are bad, normally if you replace them, you just do the upstream ones, you don't touch the downstream ones.

Honcho

The wires are bad right at the plug, so no, they cannot be fixed.

How does "...in most cases..." pertain to my situation where the codes specifically pointed to the downstream sensors, and that is where the damage is?

cetialpha5

It didn't. It was just a general observation. It's just too bad the mice got to it, they might have lasted a long time. It's too bad you can't swap the upstream with the downstream, usually the only difference is the length of the wire, the sensor for both is usually the same.

Plutoe

" usually the only difference is the length of the wire, the sensor for both is usually the same."------WFPDYCF!!!

Hint W=what
F=from

Honcho

Update: After seeing the wires, I don't think it was mice. It looks more like a previous repair that required that the sensors be removed, maybe to remove the cat or exhaust system to get to whatever... (transmission?), was done by some F-Tard that used an inappropriate tool or force to yank them out. My indy echoed that conclusion.

I'm glad to have a master mechanic I trust, and wish the previous owner had had one!

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