Post cat sensor failing? W210 2001 E430

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MB Enthusiast
Jul 31, 2008
The silver one.
Plugged my scanner into car yesterday and was watching the 02 sensors switching back and forth then noticed the post cat sensor for the right hand bank was switching very slowly and only by a very small amount.

Other 3 were switching between 0.125 ish volts to 0.750 ish volts two to three times per second.

Post one was switching between 0.630 and 0.636 maybe once a second.

So the question is, is the sensor dying (i think so) and wheres the best place to get one from?

You never know this could cure my idle misfire:)

The upstream o2 sensors should be switching but the downstream sensor should be relativley static. They measure the gasses after the cat and if they switch the same as the upstream ones they your cats aren't doing much. It may be that one of the cats is on the way out. Check to see if the cats are rattling because they can break up.
Typical and there was me thinking a nice cheap fix:( , may pop over to test station and get a smoke test done.

Anyone know which side is cylinder bank one?

Cylinder bank 1 is on the right hand side or the left if looking from under the bonnet
Alibally thanks, right hand cat it is then, new on the net £176 seems fair enough to me and of course i can sell the old one to the local scrappy for £30:D

Mate coming around tomorrow with his oscilliscope (should have been here weeks ago! his excuse heart attack:eek: whoops) to try and work out the idle misfire, which may have caused the cat failure.

Hence i dont want to fit a cat before in case it goes duff as well.

Then i think i will swap the post sensors with each other and if the fault moves its the sensor if it stays on bank one its def the cat.


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