Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Metering Module And Mixer: Notes
The metering module is responsible for injecting the urea-water solution into the exhaust pipe. It features a valve that is similar to the fuel injector in a petrol engine with intake manifold injection.
Although the metering module does not have a heater, it is still heated by the exhaust system to such an extent that it even requires cooling fins.
The metering module is actuated by a pulse-width modulated (PWM) signal from the DDE such that the pulse duty factor determines the opening duration of the valve.
The metering module is equipped with a tapered insert (6) that prevents urea-water solution residue drying up and clogging the valve. Its shape creates a flow that prevents urea-water solution from collecting on the walls of the exhaust system. Urea deposits on the insert are burnt off as it is heated to very high temperatures by the flow of exhaust gas.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.