P204F — Reductant System Performance
Reductant (AdBlue) system performance fault.
P204F is logged when the SCR control module detects the reductant (AdBlue) dosing system is not performing to its commanded output. It typically indicates the system can no longer dose enough AdBlue to keep NOx within Euro 6 limits, even though no single component has fully failed open-circuit.
P204F symptoms
- AdBlue warning light
- 'AdBlue — no engine start in X starts' countdown
- Intermittent limp mode
- Repeat dealer trips with no permanent fix
- Erratic AdBlue consumption
Common causes of P204F
AdBlue dosing pump pressure low
Pump can no longer build or hold target pressure.
Crystallised AdBlue injector
Urea deposits block the injector tip; commanded vs actual delivery drifts.
Restricted AdBlue supply line
Blocked filter or pinched line throttles supply.
AdBlue tank heater fault
Cold-weather freezing plus a failed heater stops dosing temperature being reached.
Software / EOL adaptation lost
Post battery-disconnect drift in SCR adaptation triggers a false fault.
Vehicles affected by P204F
- • Mercedes-Benz Sprinter, Vito, C-Class (OM651)
- • VW Crafter, Transporter, Tiguan (2.0 TDI)
- • Audi A4, A6, Q5 (3.0 TDI)
- • Peugeot Boxer, Partner, 308 (BlueHDi)
- • Citroen Relay, Berlingo, Dispatch (BlueHDi)
- • Vauxhall Movano, Vivaro, Astra (CDTi)
- • Renault Master, Trafic (dCi)
P204F diagnostic process
- Live data: dosing pump pressure target vs actual, dosing duty cycle, injector duration
- Visual inspection of injector and SCR inlet for crystallisation
- Flow test of AdBlue supply line and filter
- Tank heater current draw test in cold conditions
- Verify SCR adaptations and quality sensor
Common P204F repairs
- Clean or replace AdBlue dosing injector
- Replace AdBlue dosing pump assembly
- Replace blocked supply filter / line
- Repair or replace tank heater
- Reset SCR adaptations with manufacturer-level tool
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