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DTC codes / Volkswagen codes / P1121
P1121 on Volkswagen vehicles means the engine control module has detected a short to ground in the heater circuit for the downstream oxygen sensor on bank 2, which is the sensor after the catalytic converter on the bank opposite cylinder one. The computer monitors the heater element current and sees it flowing to ground before it should, indicating a wiring fault, a failed sensor heater, or a problem inside the control module.
Guidance is general and written for Volkswagen vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.
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