Under proper road conditions, when the exhaust temperature exceeds the limit value and the exhaust flow rate is in the appropriate range, the ECU calculates the SCR conversion efficiency by operating on the Nox signal; afterward, compare the calculated value with the threshold value. If the value is less than the threshold value for two consecutive times, an alarm will pop out to activate the guidance system, leading to torque and speed limit after a while.
1. Check out the AdBlue concentration by using the AdBlue gauge to see if it is 32.5%; if not, replace the AdBlue;
2. See if the AdBlue injection system works well and if the AdBlue nozzle atomizes normally.
3. Check out the exhaust box and see if massive crystals block the mixer; also see if yellow-green crystals accumulates in the diversion chamber; remove them if so. (by physical beating or regeneration)
4. Now is the Carrier efficiency check. Keep the SCR upstream temperature (T6) above 250°C for 15~20 minutes, and read the following data streams: the downstream NOX concentration value received via CAN line, the upstream NOX concentration value received via CAN line. If the difference between the upstream and downstream NOX sensor values is insignificant, then the SCR carrier may have HC or S poisoning.
5. Check out the primary exhaust emissions of the engine; fuel sampling: take 500ml fuel from the malfunctioning vehicle into a transparent container (engine fuel standards: sulfur content≤10mg/kg, cetane number≥45).
6. Add qualified fuel, then do the regeneration three times in a row (high temperature desulfurization treatment). After regeneration is completed, monitor the measured values of the upstream and downstream nitrogen and oxygen sensors again. Keep vehicle speed around 80km/h and the SCR upstream exhaust temperature around 280°C for about 30 minutes. During the process, observe the conversion efficiency (big gap between the upstream and downstream nitrogen and oxygen sensor measurement values ), and the efficiency is restored.
