Hi. I drive 2008 C300 Sport and I need some help diagnosing the problem with my car. About a week ago my CEL turned on and found a P2A00 code (oxygen sensor 1 bank 1). I read some posts and they recommended that I wipe the code and see if it comes back up. 1 week later, the CEL light is still off but I was worried so I scanned the car again using Torque.

It appears that the oxygen sensor is on the high-end of the acceptable range but is still a PASS. I also found some other FAILS using Torque but I'm not sure if those are an issue. Please help me figure out whether or not:
-I should replace the oxygen sensor (hopefully assist me if anyone has experience)
-whether or not the other FAILS are a major concern

Thank you

Test report:
------------------
MID:$01 TID:$83
- O2 Bank 1 Sensor 1
Max: 1.99882 Min: 0.3499
Test result value: 1.942
PASS
----
MID:$01 TID:$84
- O2 Bank 1 Sensor 1
Max: 0.04499 Min: -0.04499
Test result value: -0.02617
PASS
----
MID:$02 TID:$01
Rich to Lean sensor threshold voltage(constant) - O2 Bank 1 Sensor 2
Max: 0.60122V Min: 0.60122V
Test result value: 0.60122V
PASS
----
MID:$02 TID:$02
Lean to Rich sensor threshold voltage(constant) - O2 Bank 1 Sensor 2
Max: 0.60122V Min: 0.60122V
Test result value: 0.60122V
PASS
----
MID:$02 TID:$05
Rich to Lean sensor switch time(calculated) - O2 Bank 1 Sensor 2
Max: 65,535ms Min: 0ms
Test result value: 50ms
PASS
----
MID:$02 TID:$07
Minimum sensor Voltage for test cycle(calculated) - O2 Bank 1 Sensor 2
Max: 0.44969V Min: 0V
Test result value: 0V
PASS
----
MID:$02 TID:$08
Maximum sensor Voltage for test cycle(calculated) - O2 Bank 1 Sensor 2
Max: 1.1185V Min: 0.44969V
Test result value: 0.84448V
PASS
----
MID:$02 TID:$81
- O2 Bank 1 Sensor 2
Max: 0.65002V Min: 0V
Test result value: 0.64026V
PASS
----
MID:$02 TID:$82
- O2 Bank 1 Sensor 2
Max: 1.1185V Min: 0.65002V
Test result value: 0.65978V
PASS
----
MID:$02 TID:$83
- O2 Bank 1 Sensor 2
Max: 0.14933V Min: 0V
Test result value: 0V
PASS
----
MID:$02 TID:$86
- O2 Bank 1 Sensor 2
Max: 65,535ms Min: 0ms
Test result value: 1,780ms
PASS
----
MID:$05 TID:$83
- O2 Bank 2 Sensor 1
Max: 1.99882 Min: 0.3499
Test result value: 1.40837
PASS
----
MID:$05 TID:$84
- O2 Bank 2 Sensor 1
Max: 0.04499 Min: -0.04499
Test result value: 0.00213
PASS
----
MID:$06 TID:$01
Rich to Lean sensor threshold voltage(constant) - O2 Bank 2 Sensor 2
Max: 0.60122V Min: 0.60122V
Test result value: 0.60122V
PASS
----
MID:$06 TID:$02
Lean to Rich sensor threshold voltage(constant) - O2 Bank 2 Sensor 2
Max: 0.60122V Min: 0.60122V
Test result value: 0.60122V
PASS
----
MID:$06 TID:$05
Rich to Lean sensor switch time(calculated) - O2 Bank 2 Sensor 2
Max: 65,535ms Min: 0ms
Test result value: 80ms
PASS
----
MID:$06 TID:$07
Minimum sensor Voltage for test cycle(calculated) - O2 Bank 2 Sensor 2
Max: 0.44969V Min: 0V
Test result value: 0V
PASS
----
MID:$06 TID:$08
Maximum sensor Voltage for test cycle(calculated) - O2 Bank 2 Sensor 2
Max: 1.1185V Min: 0.44969V
Test result value: 0.86449V
PASS
----
MID:$06 TID:$81
- O2 Bank 2 Sensor 2
Max: 0.65002V Min: 0V
Test result value: 0.64026V
PASS
----
MID:$06 TID:$82
- O2 Bank 2 Sensor 2
Max: 1.1185V Min: 0.65002V
Test result value: 0.65978V
PASS
----
MID:$06 TID:$83
- O2 Bank 2 Sensor 2
Max: 0.14933V Min: 0V
Test result value: 0V
PASS
----
MID:$06 TID:$86
- O2 Bank 2 Sensor 2
Max: 65,535ms Min: 0ms
Test result value: 1,020ms
PASS
----
MID:$21 TID:$84
- Catalyst Monitor Bank 1
Test incomplete or dependant test failed
--
MID:$22 TID:$84
- Catalyst Monitor Bank 2
Test incomplete or dependant test failed
--
MID:$39 TID:$80
-
Max: -2,048 Min: -32,768
Test result value: -2,207
PASS
----
MID:$3b TID:$81
- EVAP Monitor (0.090")
Max: 2,181 Min: -32,768
Test result value: 518
PASS
----
MID:$3c TID:$81
- EVAP Monitor (0.040")
Test incomplete or dependant test failed
--
MID:$3d TID:$88
- EVAP Monitor (0.020")
Max: -164 Min: -32,768
Test result value: -199
PASS
----
MID:$3d TID:$8c
- EVAP Monitor (0.020")
Max: 32,767 Min: -7,373
Test result value: 950
PASS
----
MID:$41 TID:$85
- O2 Heater Monitor Bank 1 - Sensor 1
Max: 1,302.80005°C Min: 724.90002°C
Test result value: 819.90002°C
PASS
----
MID:$42 TID:$81
- O2 Heater Monitor Bank 1 - Sensor 2
Max: 936Ohm Min: 0Ohm
Test result value: 102Ohm
PASS
----
MID:$45 TID:$85
- O2 Heater Monitor Bank 2 - Sensor 1
Max: 1,302.80005°C Min: 724.90002°C
Test result value: 819.79999°C
PASS
----
MID:$46 TID:$81
- O2 Heater Monitor Bank 2 - Sensor 2
Max: 936Ohm Min: 0Ohm
Test result value: 98Ohm
PASS
----
MID:$6e TID:$33
-
Max: 817.90002g Min: 5,543.2002g
Test result value: 6,552.30029g
FAIL
----
MID:$71 TID:$80
- Secondary Air Monitor 1
Max: 1.99882 Min: 0.43725
Test result value: 1.00723
PASS
----
MID:$72 TID:$80
- Secondary Air Monitor 2
Max: 1.99882 Min: 0.43725
Test result value: 1.10874
PASS
----
MID:$81 TID:$80
- Fuel System Monitor Bank 1
Max: 4.5% Min: -4.5%
Test result value: -0.24%
PASS
----
MID:$81 TID:$82
- Fuel System Monitor Bank 1
Max: 1.29924 Min: 0.69961
Test result value: 1.07256
PASS
----
MID:$82 TID:$80
- Fuel System Monitor Bank 2
Max: 4.5% Min: -4.5%
Test result value: -0.29%
PASS
----
MID:$82 TID:$82
- Fuel System Monitor Bank 2
Max: 1.29924 Min: 0.69961
Test result value: 1.05051
PASS
----
MID:$82 TID:$cd
- Fuel System Monitor Bank 2
Max: 245.22A Min: 62.16A
Test result value: 655.20001A
FAIL
----
MID:$8f TID:$e3
-
Max: 22,677 Min: 6,176
Test result value: 7,208
PASS
----
MID:$a2 TID:$0b
EWMA Misfire counts (average) for last 10 drive cycles - Misfire Cylinder 1 Data
Max: 65,535Count Min: 0Count
Test result value: 0Count
PASS
----
MID:$a2 TID:$0c
Misfire counts for last/current driving cycles(calculated) - Misfire Cylinder 1 Data
Max: 65,535Count Min: 0Count
Test result value: 0Count
PASS
----
MID:$a3 TID:$0b
EWMA Misfire counts (average) for last 10 drive cycles - Misfire Cylinder 2 Data
Max: 65,535Count Min: 0Count
Test result value: 0Count
PASS
----
MID:$a3 TID:$0c
Misfire counts for last/current driving cycles(calculated) - Misfire Cylinder 2 Data
Max: 65,535Count Min: 0Count
Test result value: 0Count
PASS
----
MID:$a4 TID:$0b
EWMA Misfire counts (average) for last 10 drive cycles - Misfire Cylinder 3 Data
Max: 65,535Count Min: 0Count
Test result value: 0Count
PASS
----
MID:$a4 TID:$0c
Misfire counts for last/current driving cycles(calculated) - Misfire Cylinder 3 Data
Max: 65,535Count Min: 0Count
Test result value: 0Count
PASS
----
MID:$a5 TID:$0b
EWMA Misfire counts (average) for last 10 drive cycles - Misfire Cylinder 4 Data
Max: 65,535Count Min: 0Count
Test result value: 0Count
PASS
----
MID:$a5 TID:$0c
Misfire counts for last/current driving cycles(calculated) - Misfire Cylinder 4 Data
Max: 65,535Count Min: 0Count
Test result value: 0Count
PASS
----
MID:$a6 TID:$0b
EWMA Misfire counts (average) for last 10 drive cycles - Misfire Cylinder 5 Data
Max: 65,535Count Min: 0Count
Test result value: 0Count
PASS
----
MID:$a6 TID:$0c
Misfire counts for last/current driving cycles(calculated) - Misfire Cylinder 5 Data
Max: 65,535Count Min: 0Count
Test result value: 0Count
PASS
----
MID:$a7 TID:$0b
EWMA Misfire counts (average) for last 10 drive cycles - Misfire Cylinder 6 Data
Max: 65,535Count Min: 0Count
Test result value: 0Count
PASS
----
MID:$a7 TID:$0c
Misfire counts for last/current driving cycles(calculated) - Misfire Cylinder 6 Data
Max: 65,535Count Min: 0Count
Test result value: 0Count
PASS
----

 

how many miles do you have? has your mpg changed? These things dont last forever. My o2 sensor started throwing a code and then went away. It happend more and more frequently until finally i just replaced it. The mpg went back up 5mpg and I should have done it sooner.

 

I have around 43000 miles on the car. The fuel mileage does seem like it's 4mpg less than when I bought it new.

Do u recommend changing all 4 sensors? And is this something I can change on my own? Thanks

 

43K miles is pretty early for O2 sensor failures, but not unheard of. The Torque output doesn't indicate a blatant failure so you're sensors appear to be fairly OK. I would get better verification before changing all 4 sensors as the P2A00 code is specific to the bank1 'front' #1 sensor. (I doubt that all 4 are bad at this point.) From earlier reviews of this repair I found the 'rear' sensor (#2) to be pretty accessible. The 'front' #1 sensor is harder to access and will be easier with an offset O2 sensor socket.

 

I checked my sensors again and I received more fails. Does this mean I should change both bank 1 sensor 1 and sensor 2 and ALSO the fuel monitors? I'm confused as the fails come and go. I'm not sure if I trust Torque that much.

MID:$01 TID:$34
- O2 Bank 1 Sensor 1
Max: 4,096 Min: 2,667.19995
Test result value: 1,561.59998
FAIL
----
MID:$01 TID:$75
- O2 Bank 1 Sensor 1
Max: 4,096 Min: 2,667.19995
Test result value: 1,561.59998
FAIL
MID:$02 TID:$cd
- O2 Bank 1 Sensor 2
Max: 245.17999A Min: 62.16A
Test result value: 655.20001A
FAIL
MID:$81 TID:$86
- Fuel System Monitor Bank 1
Max: -2,457.6001 Min: 2,667.19995
Test result value: 1,561.59998
FAIL
MID:$81 TID:$8b
- Fuel System Monitor Bank 1
Max: -2,457.6001 Min: 1,028.80005
Test result value: 1,561.59998
FAIL

 

I'm not familiar with Torque at all, but the OBD monitoring system is an automotive standard so the basic codes extracted from the maintenance port should provide a realistic status of the emission system status.

BTW: Here are links to the replacement diy docs:

http://www.pelicanparts.com/techarti...eplacement.htm

http://www.mercedesmedic.com/how-to-...mercedes-benz/

 

So I tried replacing the upstream oxygen sensor myself and failed. The sensor was stuck. I ended up going to an indy to get it replaced.

They simply accessed the O2 sensor from the top of the engine, through a small compartment where you can see the sensor, using a long extension. For DIYers, check if you can see the o2 sensor from the engine bay. It's much easier to access. It took the indy about 2 mins to get it loose.

Cheers.