I have a Mercedes ML 320, 2000.


I just replaced all four oxygen sensors but the "Check Engine" has returned right after the replacement. 


The codes that have been indicated: 157, 161, 135, 155, 141 and 134.


Do you know why those codes would appear even with all brand new Bosch oxygen sensors? 


I am so puzzled...






I am not sure what it can be but let me list the meanings of each of these and it might give you some clue on what is wrong here:


1. P0157 = O2 Sensor Circuit Low Voltage (Bank 2, Sensor 2)

2. P0161 = O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2) – Downstream

3. P0135 = Heated Oxygen Sensor Heater Circuit Malfunction (Bank1 Sensor1)

4. P0155 = 02 Sensor Heater Circuit Malfunction (Bank 2, Sensor 1

5. P0141 = O2 Sensor Heater Circuit Malfunction

6. P0134 = O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)

From the information you provided and the meanings of these fault codes, it is pretty much clear that there is a presistent problem with your O2 Sensor heater and there is a malfunction in the circuit. Both in Bank 1 and Bank 2, as well as a problem in both sensors.


Since you have replaced the sensors, it means the problem is actually the heart circuit  in Bank 1 and Bank 2. Please check those.

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