P0137 low voltage O2 sensor bank 1 sensor 2 W205

[Howard_silver]

The EML illuminated last month on our W205 C200 petrol 7G automatic. I possess an iCarsoft reader that indicated a low voltage fault for O2 sensor bank 1, sensor 2. I cleared the issue, but it reappeared after several cold drives.

I have substituted the oxygen sensor (Bosch component) and erased the mistake. Upon the service interval, I performed an oil and filter change and changed the spark plugs, as the vehicle has reached 38,000 kilometres and is now 8 years old (2016). I believed this issue had been resolved, but after five drives from a perfectly cold start, it reoccurred today. The MOT is scheduled for next week, and although I believe I may pass by resetting it just prior to the examination, I am want to thoroughly understand the underlying issue.


I believe 'Star' readers may provide additional insights, so I may need to consult a local Mercedes specialist, since I prefer not to engage with the major dealer due to a negative experience with them during my tenure with company cars before to retirement. I am willing to conduct any additional physical or visual inspections prior to reaching that level; thus, I am publishing here to solicit comments or insights from others who have encountered this issue.

[alpaco45]

The second O2 sensor is positioned subsequent to the catalytic converter. This indicates that the mixture is deficient—excess oxygen may be due to an air leak in the exhaust system, or the ECU may have reached the rich limit for closed-loop control, yet insufficient fuel is still being injected—possibly due to low fuel pressure or malfunctioning injectors. Examine the current reading of O2 sensor 2; there may be a disruption in the wiring to it. Verify the measurements for O2 sensor 1 (pre-catalytic converter). If this is operating normally (0.2 - 0.8 volts every few seconds), with a lambda reading of approximately 1.00 once the engine has reached optimal temperature.

The post-catalytic converter O2 sensor typically provides a consistent value of approximately 0.5 volts.


If a physical inspection of the exhaust manifold, pipes, and catalytic converter appears satisfactory, there are no obvious leaks on the inlet manifold, and the fuel pressure is adequate, it may be prudent to consult an expert.

[alpaco45]

https://en.wikipedia.org/wiki/Oxygen_sensor

[alpaco45]

I am confident that superior explanations can be found online.

[Howard_silver]

Thank you for your response, alpaco45.

I have inspected the wiring from the sensor to the best of my ability, albeit it vanishes into the loom within the confines of the engine compartment. Additionally, verified the earth continuity to the sensor's body, which measured approximately 0 ohms, indicating a satisfactory connection. The pre-catalytic converter sensor activates, as you indicated, once it reaches operational temperature, while both the pre- and post-catalytic converter sensors appear to initiate at a constant voltage during open-loop mode during warm-up, with typical 'cold start' values of 1.275V for the pre-catalytic converter and 0.200V for the post-catalytic converter.


Infrequently, when starting from a cold state, the post-catalytic converter oxygen sensor displays 0.000 volts during open loop mode; however, it is uncertain if this is a misleading indicator.

I operated the vehicle as my wife observed the live data, and the two sensors appeared to fluctuate in unison after they reached optimal temperature, with the pre-catalytic converter value generally elevated and the lambda reading approximately 1.000 as well.

I have thoroughly inspected the exhaust from beneath and seen no visible or audible signs of a leak. I have seen a high-pitched screech when the engine is shut off, which has been occurring for an extended period prior to the illumination of the EML. The scream ceases when the throttle body undergoes a reset (I can detect a clicking sound from that region after powering off), but it occasionally reemerges. I have attempted to identify the source of the scream; but, its intermittent nature complicates the determination of whether applying pressure to a pipe or component influences it.

I believe I may need to consult an expert regarding Star. I detest capitulating, and I wish to prevent them from indiscriminately hurling components at the vehicle in an attempt to rectify it; therefore, I aim to ensure that I have thoroughly examined all possibilities beforehand. I will need to subject it to the MOT to determine whether any issues are identified. I have a family visit approaching, therefore I will have limited time for repair work following the MOT due to poor scheduling. I am disinclined to undertake a 300-mile drive in our Alfa Mito, therefore I may ultimately resort to renting a vehicle at this pace. 😞

The EML activates earlier when my wife operates the vehicle.I typically drive more cautiously, whereas she accelerates more aggressively between traffic signals. The EML may activate after two drives with her, whereas it may require over five drives with me; nevertheless, I am uncertain how to interpret this. 😄

[drummer]

If the catalyst is functioning properly, the pre and post sensors should not exhibit correlated readings. The pre-catalyst sensor should approximately adhere to a sine wave pattern. The post-catalyst sensor should register a low value if the catalyst is functioning effectively.

[Howard_silver]

That appears unfavourable. It is really unfortunate that the vehicle has only endured 38,000 miles.

The back O2 sensor occasionally registers around 0.200V with few fluctuations, whilst the pre-catalytic converter sensor exhibits erratic behaviour. I have utilised a cat cleaner in the vehicle; nevertheless, it seems to have little effect. I tend to view additives as quite desperate measures, to be frank.


The vehicle may fail the MOT on emissions if the catalytic converter is malfunctioning, irrespective of whether the engine management light is illuminated at that moment.

On the positive side, I can replace it independently; however, on the negative side, it will not be inexpensive if it proves to be the issue. 😞

[Geek2232]

An illuminated EML will inevitably result in failure.

[Howard_silver]

I appreciate that; but, I always manage to clear the EML, and it remains off for several days. I am merely hoping to pass the MOT with the light extinguished. I may address the matter at my convenience.

[Howard_silver]

I wanted to inform you that after visiting a local Mercedes-Benz specialist who merely reset the Engine Management Light, I opted to purchase a real Mercedes-Benz sensor, as it was their subsequent recommendation. I am uncertain why the Bosch unit I installed last year was ineffective; it may be counterfeit, but I cannot verify this. I successfully procured an authentic new MB part directly from Germany through eBay for £103, in contrast to nearly £300 from Sytner Newcastle, not accounting for the potential markup and labour costs if a professional had provided and installed it.

After removing and reinstalling the component several times, including refitting the original MB part, I completed the replacement in under 10 minutes, as the lower covers were already removed. I rectified the problems, and we have completed approximately twelve flights from a cold start. Previously, the EML would activate after 3-4 visits, and I observed several 'pending' problems on my code reader prior to that. It successfully passed its MOT today without any prior manipulation, so I am optimistic that this resolves the issue.


I anticipate achieving substantial mileage from this replacement part, and I expect the MPG will return to the prior mid-40s during a run, rather than just over 40 MPG.

The implication is to exclusively utilise authentic MB components; nevertheless, I believe that companies like Bosch should be competent enough to perform well, particularly given the exorbitant costs imposed by MB at retail. It is advantageous to compare prices and engage in some do-it-yourself activities.