P204F — Reductant system, bank 1 — performance fault

P204F concerns reductant system, bank 1. The monitor reports that the named control function does not meet its expected operating behavior. The code describes overall reductant-system performance. Its wording does not isolate a pump, injector, fluid-quality problem or other individual cause.

Affected system: Reductant dosing and SCR aftertreatment

Symptoms

• A warning for the engine or DEF emissions system may appear.
• Some vehicles reduce engine output while an SCR fault persists.

Possible causes

• Insufficient or contaminated DEF can affect reductant-system performance.
• A pump, injector, pressure sensor or fluid line can be faulty or obstructed.
• The SCR control circuit or electrical connections may require investigation.

What to check

• Inspect DEF level and fluid condition; read related SCR fault codes.
• Examine dosing-system wiring, hoses and connectors for leaks or damage.
• Check pressure feedback and perform manufacturer-approved pump and dosing-valve tests where supported.

Also written as: P204F-00, P204F00 (some scan tools add the fault-type byte, e.g. -00).