p0136 - Rear o2 Sensor - 99 C230K Troubleshooting

[xvvvz]

I do NOT have a CEL light but recently plugged in my very basic OBD II scanner (no live data graphing or anything) and recieved a P0136 code. This the o2 Sensor Circuit Malfunction (Bank 1, Sensor 2) error which indicates the o2 oxygen sensor after the catalytic converter. There are no other codes.

When I try to clear the code with my scanner, the code comes back immediately without even starting the engine.

My 99 c230 Kompressor with the M111.975 engine has just under 40k miles. The gas mileage has been low for quite some time but the car runs smoothly and doesn’t misfire. I recently replaced the MAF with a new Bosch unit from Autohausaz.com but the code was there before the MAF replacement and after (it is a long story but I have had a suspicion my MAF was unreliable for a long time). I am very confident that all of the intake connections from the intercooler back to the throttle body (including the MAF) are not leaking.

Any help troubleshooting this would be appreciated. Is this one of those issues where I need to go get it diagnosed with a high tech system like the Mercedes SDS diagnostics versus just replacing o2 sensor or is it pretty certain with this code that the problem is going to be sensor itself?

Is it possible on the w202 C Class to disconnect the rubber exhaust hangers from the cat back and be able to get enough clearance to swap out the rear o2 sensor (located on top of the exhaust pipe, unfortunately) with the car up on ramps or do I have to disassemble the whole exhaust system?

Is an o2 socket wrench necessary or will an open wrench work just fine? If a socket is necessary, is the full socket (like a lawn mower spark plug wrench) best or is the smaller crow’s foot type better?

Any advice would be appreciated.

Thanks!

[SLAMMED_C]

is the malfunction the heater circuit in the rear o2 sensor?
its odd that the code comes back right away but yet there is no check engine light on at all.
you could have possible 1 of 2 issues.. either the o2 sensor itself it faulty, or the ME is faulty. Ive only ever seen one ME be faulty causing the o2 sensor code to appear.. any other time it has been a faulty o2 sensor.
Id try th o2 first as its hella cheaper then the ME!
But I cant guarantee its the problem as I cant diagnose a car if its not in my possession.

as for replacing it.. I dont exactly remember where on the exhaust its located (in the "v" of the catalysts at the back?) I would say yes try and lower the exhaust partially to give you some room, then you can either use an o2 sensor socket.. or a 22mm wrench.
Good luck.

[xvvvz]

Thanks for the reply.

The P0136 code does not specifically address the heater like some of the other codes do. It seems just like a general fault code. Here are the o2 sensor related codes:

# P0130 02 Sensor Circuit Malfunction (Bank I Sensor 1)
# P0131 02 Sensor Circuit Low Voltage (Bank I Sensor I)
# P0132 02 Sensor Circuit High Voltage (Bank I Sensor 1)
# P0133 02 Sensor Circuit Slow Response (Bank 1 Sensor 1)
# P0134 02 Sensor Circuit No Activity Detected (Bank I Sensor 1)
# P0135 02 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)
# P0136 02 Sensor Circuit Malfunction (Bank I Sensor 2)
# P0137 02 Sensor Circuit Low Voltage (Bank I Sensor 2)
# P0138 02 Sensor Circuit High Voltage (Bank I Sensor 2)
# P0139 02 Sensor Circuit Slow Response (Bank 1 Sensor 2)
# P0140 02 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)
# P0141 02 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)
# P0142 02 Sensor Circuit Malfunction (Bank I Sensor 3)
# P0143 02 Sensor Circuit Low Voltage (Bank I Sensor 3)
# P0144 02 Sensor Circuit High Voltage (Bank I Sensor 3)
# P0145 02 Sensor Circuit Slow Response (Bank 1 Sensor 3)
# P0146 02 Sensor Circuit No Activity Detected (Bank I Sensor 3)
# P0147 02 Sensor Heater Circuit Malfunction (Bank I Sensor 3)
# P0150 02 Sensor Circuit Malfunction (Bank 2 Sensor I)
# P0151 02 Sensor Circuit Low Voltage (Bank 2 Sensor I)
# P0152 02 Sensor Circuit High Voltage (Bank 2 Sensor 1)
# P0153 02 Sensor Circuit Slow Response (Bank 2 Sensor 1)
# P0154 02 Sensor Circuit No Activity Detected (Bank 2 Sensor 1)
# P0155 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
# P0156 02 Sensor Circuit Malfunction (Bank 2 Sensor 2)
# P0157 02 Sensor Circuit Low Voltage (Bank 2 Sensor 2)
# P0158 02 Sensor Circuit High Voltage (Bank 2 Sensor 2)
# P0159 02 Sensor Circuit Slow Response (Bank 2 Sensor 2)
# P0160 02 Sensor Circuit No Activity Detected (Bank 2 Sensor 2)
# P0161 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2)
# P0162 02 Sensor Circuit Malfunction (Bank 2 Sensor 3)
# P0163 02 Sensor Circuit Low Voltage (Bank 2 Sensor 3)
# P0164 02 Sensor Circuit High Voltage (Bank 2 Sensor 3)
# P0165 02 Sensor Circuit Slow Response (Bank 2 Sensor 3)
# P0166 02 Sensor Circuit No Activity Detected (Bank 2 Sensor 3)
# P0167 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 3)

>>I dont exactly remember where on the exhaust its located (in the "v" of the catalysts at the back?) <<

Yes, that is correct.

Which sensor socket type do you think is best/most versatile? The tall one like a spark plug socket or the open crow's foot type? Given that I may be working in a tight space, I am wondering if the shorter crow's foot type might be better. I just have never used one before, so I don't know if there are other pitfalls with them.

I think I am going to get it back up on ramps and check the power cableing and maybe see if I can do the wiggle test to make sure it is tight and making contact. Supposedly it is pretty rare for these to go out.

Thanks for any insights!

[SLAMMED_C]

Originally posted by xvvvz
Thanks for the reply.

The P0136 code does not specifically address the heater like some of the other codes do. It seems just like a general fault code. Here are the o2 sensor related codes:

# P0136 02 Sensor Circuit Malfunction (Bank I Sensor 2)

>>I dont exactly remember where on the exhaust its located (in the "v" of the catalysts at the back?) <<

Yes, that is correct.

Which sensor socket type do you think is best/most versatile? The tall one like a spark plug socket or the open crow's foot type? Given that I may be working in a tight space, I am wondering if the shorter crow's foot type might be better. I just have never used one before, so I don't know if there are other pitfalls with them.

I think I am going to get it back up on ramps and check the power cableing and maybe see if I can do the wiggle test to make sure it is tight and making contact. Supposedly it is pretty rare for these to go out.

Thanks for any insights!

I would definitely check the feed from the me to the o2 sensor plug itself to make sure you are good that way. check continuity through the wires.. if all is good I'd say you have a faulty o2 sensor.
the best O2 sensor socket is one like..
http://www.SamstagSales.com/mercedes/mb000589710300.jpg
the shorter (crows foot like) socket, but with it being in the "v" of the catalyst you may be better off with a deeper o2 socket. If sure you could easily use a 22mm wrench.
It isn't as common for the rear o2 to go.. but I have seen them.

[xvvvz]

Ok, thanks.