NOx, EGT and smart exhaust sensors
SCR efficiency fault remains after parts have been changed. Which sensor is actually telling the ECU whether the aftertreatment system worked?
What this lesson covers
CORE TEACHING Upstream/downstream NOx sensors; integrated sensor control modules; heater/warm-up; CAN/LIN-style smart sensor communication depending on platform; NOx ppm interpretation; EGT sensor role in turbo/DPF/SCR protection; plausibility comparisons; wiring/power/network faults; sensor ageing/contamination. PRACTICAL DEMONSTRATIONS AND TESTS Cold-soak compare EGT sensors; graph EGT through warm-up/regen; compare upstream/downstream NOx during stable conditions; verify sensor module power/ground/network; use scan data to distinguish ‘no data’, implausible data and genuine high NOx. ADVANCED / SCAN TOOL LAYER Scan ppm/temperature; network DTCs; scope communication only where service information supports the physical layer; power/ground loaded tests. KEY DIAGNOSTIC QUESTIONS Is the sensor awake and communicating? Has it reached operating temperature? Do upstream/downstream readings make chemical sense with SCR command? MUST-COVER CHECKPOINTS Sensor power/ground/network; warm-up; plausibility; compare like sensors cold; upstream/downstream result; link reading to aftertreatment command.
What you will be able to do
SCR efficiency fault remains after parts have been changed. Which sensor is actually telling the ECU whether the aftertreatment system worked?
Where it sits in the programme
- Builds on
- Lesson 45: AdBlue / SCR system diagnosis
- Feeds into
- Lesson 47: Power–ground–signal: the default framework