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O2 SENSOR CHECK ENGINE
Thread Starter
Junior Member
Joined: Apr 2006
Posts: 53
Likes: 0
From: Simi Valley
2003 E320
O2 SENSOR CHECK ENGINE
Hi Guys my Check Engine light turned on my car today and I looked up the code with my OBD computer. It says I have two faults which are: "p0151 O2 Circuit low voltage (bank 2. Sensor 1). And P0400 exhaust gas recirculation Flow. My question which O2 sensor is the one I have to buy I went online and there are several different ones. And is the second code caused by the O2 sensor not working. I tried looking under search but could not find anything. Thanks
Member
Joined: Jan 2012
Posts: 244
Likes: 4
From: PA, USA
2004 E320 4matic Sedan
some comments
You asked if this O2 sensor (and code) is causing the other EGR P0400 code. I suspect the opposite chain of causation.
P0151 relates to the O2 sensor in front of the catalyst for bank 2. (that is, the side that does not include cyl #1, just to be convoluted). P0151 means the sensor is giving a low voltage. That could mean it is not working properly or, if it is in fact correct and honest, that it is seeing a lean condition. The OS sensor gives a low voltage when the exhaust gases are lean, and a higher voltage when the exhaust gases are rich. Just because the sensor is resulting in a code doesn't mean it's broken. It is supposed to tell it how it sees it. Maybe it's accurately reporting the truth!
As for the other code, P0400 = exhaust gas recirculation flow malfunction. That is saying that your car is not correctly recirculating exhaust gases. That could make the mixture too lean or too rich. If you believe the O2 sensor, it is the former that is happening - too lean. Even a bad O2 sensor isn't going to break the exhaust gas recirculation system and make it throw a code.
I suspect you have an EGR (exhaust gas recirclation) valve that is not working properly, causing an "exhaust gas recirculation flow malfunction" and a lean condition and that is having a knock-on effect on one of your O2 sensors. Why on only one side, I don't know, but I would randomly chuck money at a new EGR valve before a new 02 sensor, based on the evidence.
Alternatively, the EGR valve may be OK but you may have a leak in the EGR circuit or perhaps a tube unplugged in the egr circuit.
We all learn by being wrong, so if it turns out I am wrong, please post back once you bottom the issue out.
Good luck!
P0151 relates to the O2 sensor in front of the catalyst for bank 2. (that is, the side that does not include cyl #1, just to be convoluted). P0151 means the sensor is giving a low voltage. That could mean it is not working properly or, if it is in fact correct and honest, that it is seeing a lean condition. The OS sensor gives a low voltage when the exhaust gases are lean, and a higher voltage when the exhaust gases are rich. Just because the sensor is resulting in a code doesn't mean it's broken. It is supposed to tell it how it sees it. Maybe it's accurately reporting the truth!
As for the other code, P0400 = exhaust gas recirculation flow malfunction. That is saying that your car is not correctly recirculating exhaust gases. That could make the mixture too lean or too rich. If you believe the O2 sensor, it is the former that is happening - too lean. Even a bad O2 sensor isn't going to break the exhaust gas recirculation system and make it throw a code.
I suspect you have an EGR (exhaust gas recirclation) valve that is not working properly, causing an "exhaust gas recirculation flow malfunction" and a lean condition and that is having a knock-on effect on one of your O2 sensors. Why on only one side, I don't know, but I would randomly chuck money at a new EGR valve before a new 02 sensor, based on the evidence.
Alternatively, the EGR valve may be OK but you may have a leak in the EGR circuit or perhaps a tube unplugged in the egr circuit.
We all learn by being wrong, so if it turns out I am wrong, please post back once you bottom the issue out.
Good luck!
Last edited by ozusa; Feb 21, 2013 at 09:43 PM. Reason: typo
