radeko1

Hello, please help.
Got codes P0133 (O2 bank1 sensor1 slow response) and P0140 (bank1 sensor2 no activity?). Replaced both sensors with OEM Bosch and cleared codes. Got the same errors. Cleaned MAF just in case, checked electrical connections, and checked for exhaust leaks. Same errors are comming back.
Searched web: code P0140 is not listed in Mercedes startechinfo.com, it is probably a generic OBD. Found info somewhere that 140 follows P0133 so I should concentrate on this one. Also, don't think it is fuel trim because it relates to one bank only. FYI: use Actron reader and E420 has 130k miles. Works fine but I want to clear CEL.
Additional info: when criss cross wires on left and right sensors got many codes related to malfunctioned sensors and missfire (but no 133) - which means that both sensors are read by the ECM.
Any suggestions?

petkennel

Thanks to Ohlord, I now am qualified to answer this concern, because it just happened to me. The P0140 code is a EGR Flow Malfunction, will also send the O2 code as well. You most likely do not need a new O2 sensor or and EGR valve (as I found out the hard way, damm!). Your EGR Flow tube is clogged with carbon. Once you clear it, the code will go away. Too bad you installed the O2 sensor, as I did, because you cannot return it now.

ohlord

is egr.
His is o2 related.

petkennel

Mine was an O2 code as well, but in the end, it was EGR Flow Tube. P0140 is EGR flow code?

radeko1

Thank you for response, I still need help.

1. update on P0133: I measured voltage at the sensors with voltmeter. All sensors read .44V with KeyOnEngineOff and cold engine running. With hot engine running: Bank 1 sensors: S1 .1-.8V flactuates fast all the time. S2 flactuates slow and is more speed dependent: .2V @low, .7V @hi RPM. Sensors on Bank2 have the same reading as on Bank1 except S2 is not speed dependent. Keep in mind that I don't know what the ECM is reading but should be the same. Again: both sensors on Bank1 are new.


2. re. EGR: I don't think that my 1997 E420 has EGR valve, other models do: 94-95 E420, 97 E320, and E430. My car has only secondary air pump+flow valve+solenoid+vacuum check valve (some parts dealers call the check valve the EGR by mistake) for warming up the cat. I can't find the EGR valve with pipe which can be pluged and no info on it. I checked all air pump system devices and they are OK. Code P0140 refers to oxygen sensor. Please correct me if I'm wrong about the EGR on my model.

3. re: code P0140. does any one know why this code is not listed on the official Mercedes Startech list for my car? Is it valid code for this year/model or just a generic OBD picked up by my reader? On the other hand why the ECM would report it?

4. unrelated question: when I search forums for "P0133" my post doesn't show up. It appears only if I search by my name. Why?

Thanks for your help.

petkennel

Darn, I was so excited I had an answer. I will refrain, and leave it up to the experts.

radeko1

Problem solved.
I rechecked everything and found super small exhaust leak. It was a hairline crack in the first, upstream CAT on the weld where cone is attached to the cylinder. Crack was so small that at low idle leak was only detectably when CAT was still cold. It is hard to belive system is so sensitive. After welding and several drive cycle (system goes through some kind of adjustment for the first 3-5 drive cycles) the codes did not showed up anymore.
Found similar problem and solution on the other forum.
So if you have both codes first check for the exhaust leak before the oxygen sensor replacement.