AdBlue / SCR system diagnosis
Countdown says ‘no start in 500 miles’ and the customer assumes it only needs AdBlue. How do you diagnose the complete SCR system instead of just topping up the tank?
What this lesson covers
CORE TEACHING SCR purpose; AdBlue/DEF composition concept; tank level/temperature/quality sensing; heaters; pump/supply module; pressure; injector/doser; heated lines; crystallisation; contamination; dosing conditions; reductant quality faults; start-inhibit/countdown logic; safe handling and correct fluid specification. PRACTICAL DEMONSTRATIONS AND TESTS Full scan; check AdBlue level/quality/temp PIDs; command pump/heater/doser where supported; inspect for crystallisation/leaks; verify supply pressure against OEM data; electrical tests on heater/pump circuits; never bypass emissions systems. ADVANCED / SCAN TOOL LAYER Bidirectional pump/doser tests; pressure/temperature/level PIDs; current draw; CAN/LIN communication to smart tank/pump modules where applicable. KEY DIAGNOSTIC QUESTIONS Is there usable fluid? Can the system build pressure? Can it dose? Are heaters/sensors believable? Does downstream NOx show the expected result? MUST-COVER CHECKPOINTS Tank data; fluid condition; heater; pump/pressure; heated line; doser; NOx before/after; countdown logic; repair verification.
What you will be able to do
Countdown says ‘no start in 500 miles’ and the customer assumes it only needs AdBlue. How do you diagnose the complete SCR system instead of just topping up the tank?
Where it sits in the programme
- Builds on
- Lesson 44: DPF regeneration diagnosis — why a regen will not complete
- Feeds into
- Lesson 46: NOx, EGT and smart exhaust sensors