Reductant Control Module
The controller that decides how much exhaust fluid to inject, and when — the brain of the SCR system rather than any of its plumbing.
It is worth knowing what it is actually calculating. Nitrogen oxide output is not measured directly at the point of dosing; it is predicted from engine load, speed, temperature and the NOx sensors either side of the catalyst. The module doses ammonia into a moving exhaust stream for a reaction happening a moment later, and it has to get the quantity right in both directions: too little leaves nitrogen oxides unconverted, too much lets ammonia through the catalyst untouched, which is its own emissions problem and smells of it.
It also protects the fluid. Exhaust fluid freezes at about minus eleven degrees, so the module runs tank and line heaters, decides whether the fluid is thawed enough to dose, and purges the lines back to the tank at shutdown so nothing is left to freeze and split a pipe.
Where it lives is what usually breaks it. On most vehicles it is mounted on or beside the tank, underneath, in the worst position on the car for road spray and salt — so its connector and harness account for a large share of the faults attributed to it.
And its failures escalate on a legal schedule rather than a mechanical one. A vehicle that cannot dose is required to make that impossible to ignore, so warnings give way to a speed limit and eventually to a vehicle that will not restart — which is why a fault here matters long before anything feels wrong to drive.
Also known as: DEF control module, diesel exhaust fluid control unit, AdBlue control module, urea dosing module, SCR control module, reductant dosing control unit
Referenced by 24 codes
Codes involving this component (24)
- U010E Lost Communication With Reductant Control Module High
- P056D Reductant Control Module System Voltage
- P05ED Reductant Heater Control Module Supply Voltage
- P05F3 Exhaust Aftertreatment Power Relay Control Circuit/Open
- P05F4 Exhaust Aftertreatment Power Relay Control Circuit Low
- P05F5 Exhaust Aftertreatment Power Relay Control Circuit High
- P05F6 Exhaust Aftertreatment Power Relay Control Circuit Stuck On
- P05F7 Exhaust Aftertreatment Power Relay Control Circuit Stuck Off
- P065D Reductant System Malfunction Lamp Control Circuit
- P06F0 Reductant Control Module Internal Temperature Sensor Circuit
- P06F1 Reductant Control Module Internal Temperature Sensor Range/Performance
- P06F2 Reductant Control Module Internal Temperature Sensor Circuit Low
- P06F3 Reductant Control Module Internal Temperature Sensor Circuit High
- P20C9 Reductant Control Module Requested Malfunction Indicator Lamp Illumination
- P20EA Reductant Control Module Power Relay De-Energized Performance — Too Early
- P20EB Reductant Control Module Power Relay De-Energized Performance — Too Late
- P20FF Reductant Control Module Performance
- P21C7 Reductant Control Module Power Relay/Relays Control Circuit/Open
- P21C8 Reductant Control Module Power Relay/Relays Control Circuit Low
- P21C9 Reductant Control Module Power Relay/Relays Control Circuit High
- P21CA Reductant Control Module Supply Voltage Circuit
- P21CB Reductant Control Module Supply Voltage Low
- U030F Software Incompatibility With Reductant Control Module
- U040F Invalid Data Received From Reductant Control Module
Other components in Exhaust and Emissions
- Oxygen Sensor 326
- EGR Valve 150
- Catalytic Converter 142
- NOx Sensor 118
- Reductant Injector 107
- Exhaust Gas Temperature Sensor 95
- Reductant Tank 95
- Diesel Particulate Filter 76
- SCR Catalyst 65
- EGR Cooler 62
- Exhaust Gas Differential Pressure Sensor 58
- Fuel Tank Pressure Sensor 58
- Exhaust Pressure Control Valve 56
- Reductant Heater 55
- Reductant Pump 51
- EVAP Vent Valve 43
- Exhaust Aftertreatment Fuel Injector 42
- Charcoal Canister 33
- EGR Position Sensor 32
- Secondary Air Injection Pump 32
- Reductant Temperature Sensor 29
- EVAP Leak Detection Pump 29
- EVAP Purge Valve 27
- Particulate Matter Sensor 24
- Reductant Level Sensor 23
- Secondary Air Switching Valve 22
- EGR Temperature Sensor 21
- Secondary Air Check Valve 21
- Catalyst Heater 20
- Catalyst Temperature Sensor 20
- Fuel Filler Cap 18
- EGR Cooler Bypass Valve 16
- Reductant Quality Sensor 16
- Exhaust Back Pressure Sensor 15
- Purge Flow Sensor 13
- Direct Ozone Reduction Catalyst 13
- EGR Vacuum Solenoid 9
- Fuel Vapour Temperature Sensor 5
- Fuel Additive Control Module 4
- Fuel Additive Tank 4
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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