C55 Pre-Primary Cat Oxygen Sensor Replacement
Thread Starter
Member
Joined: Mar 2010
Posts: 139
Likes: 5
From: PMW
2021 GLE450, 2005 C55, 1990 500SL, 1991 300E, 2006 BMW M5
C55 Pre-Primary Cat Oxygen Sensor Replacement
Hello All,
I have been replacing a lot of wear and tear items over the past few weeks on my 115K mile C55 to restore the new car feeling and do a little preventative work while I am in the garage.
One big thing I still need to tackle are the pre-primary cat oxygen sensors. After pulling off the front decorative engine cover and air box, I can see the oxygen sensors and their cables, but I have no idea how to get a wrench in there to unthread the sensors from their bungs.
Does anyone have any tips or tricks on how to get these sensors swapped out? It is really crowded in there near these sensors.
Thank you
I have been replacing a lot of wear and tear items over the past few weeks on my 115K mile C55 to restore the new car feeling and do a little preventative work while I am in the garage.
One big thing I still need to tackle are the pre-primary cat oxygen sensors. After pulling off the front decorative engine cover and air box, I can see the oxygen sensors and their cables, but I have no idea how to get a wrench in there to unthread the sensors from their bungs.
Does anyone have any tips or tricks on how to get these sensors swapped out? It is really crowded in there near these sensors.
Thank you
Last edited by Rahulio1975280C; Apr 13, 2016 at 11:38 AM.
Junior Member
Joined: Dec 2013
Posts: 30
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From: Michigan
Mercedes C55 AMG, MB GLE400, Porsche 997, Ford Focus ST, Honda Accord
1st question, why are you changing them? do you have any Pcodes suggesting that the O2 sensors are faulty? If not, leave them.
Thread Starter
Member
Joined: Mar 2010
Posts: 139
Likes: 5
From: PMW
2021 GLE450, 2005 C55, 1990 500SL, 1991 300E, 2006 BMW M5
I want to change them as I am getting odd voltage readings for one of these sensors in both of the OBDII scanner apps I use. Sometimes the readings for both sensors are the same, other times one of the two starts reading erratically between 0.0V and 0.6V, when that happens, my idle starts to fluctuate regardless of gear position. It is not horrible, but I am suspecting that one of these two pre-primary car sensors is on it's last legs, hence the replacement. I am not getting any codes, pending or logged, yet.
