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Discussion Starter · #1 ·
Since yesterday I have the CEL on on my CLA 250 C117.344 - 2L Gas 2014 (135K km/ 84K miles).

I have hooked my ODB2 reader and it announces the following DTC:

P0428: Powertrain Systems

Catalyst Temperature Sensor High Input Bank 1 Sensor 1

Possible causes:
• Faulty Catalyst Temperature Sensor
• Catalyst Temperature Sensor harness is open or shorted
• Catalyst Temperature Sensor circuit poor electrical connection

Technical notes:
As the code description implies the P0428 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem. If the P0428 code is combined with other codes, try fixing the other codes first.

Possible symptoms:
• Engine Light ON (or Service Engine Soon Warning Light)

The Engine Control Module (ECM) monitors the switching frequency ratio of heated oxygen sensors 1 (front O2 sensor) and heated oxygen sensors 2 (rear O2 sensor).

A three way catalyst converter (Manifold) with high oxygen storage capacity will indicate a low switching frequency of heated oxygen sensor 2. As oxygen storage capacity decreases, the heated oxygen sensor 2 switching frequency will increase.

When the frequency ratio of heated oxygen sensors 1 and 2 approaches a specified limit value, the three way catalyst malfunction is diagnosed.

Is the reading correct from your point of view ? Exhaust sensor value too high or faulty ?

Does someone has a plan which shows where the sensor is located? Bank 1 Sensor 1.

Does someone has experienced the same issue ?

Faulty Sensor or a more complicated issue ?

Thanks a lot for your help/comments.

1,738 Posts
I would say it might be your upstream 02 sensor on the cat. how is the car running? rich?
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