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.
Selective Catalytic Reduction (SCR) System - Transit
The SCR system reduces nitrogen oxides (NOx) in the exhaust stream by a chemical reduction process using the SCR catalyst and a reductant injection system that introduces diesel exhaust fluid (DEF) into the exhaust system upstream of the SCR catalyst. The reductant injection system is directly controlled and monitored by the reductant dosage control module. For additional information on the SCR system components, refer to ENGINE CONTROL COMPONENTS .
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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.