Code Definition

P200B — Main Catalyst Operating Efficiency Below Threshold - Bank 1

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Mercedes-Benz

About P200B

P200B is a generic (obd-ii standard) powertrain diagnostic trouble code recorded for Mercedes-Benz vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P200B is stored, the module has detected a signal or supply voltage lower than the expected operating range; and a bank-specific fault, meaning it applies only to one cylinder bank of a multi-bank engine.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P200B is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

This fault code is triggered when the engine control module (ECM) detects that the catalytic converter on Bank 1 is not operating efficiently. The ECM monitors the oxygen sensor readings before and after the catalyst to determine its efficiency. If the post-catalyst oxygen sensor signal closely follows the pre-catalyst sensor signal, it indicates that the catalyst is not adequately converting exhaust gases, setting the fault.

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