It is not false to say that vehicles contribute greatly to polluting the environment, however, attempts have been made by the vehicle manufacturers to curb this participation and promote a safer environment by reducing emissions of nitrogen oxide (NOX), Particulate matter (PM) and other pollutants. If you own a diesel-powered car, NOX sensor or PM sensor is critical to the Adblue SCR system to ensure your vehicle is compliant with the laws. In adherence to EPA emissions standards, in all newer models, this Adblue technology comes as a standard and most VW Audi Seat Skoda vehicle models are now provided with a BlueTec Technology, which utilizes Adblue Diesel Exhaust Fluid into the exhaust gas stream to reduce NOX emissions.
It is necessary that you maintain the proper levels of Adblue fluid in your vehicle or you may receive different messages popping up on your dashboard with regards to the Adblue levels such as:
- Refill AdBlue at Workshop
- AdBlue Check Additive See Operator’s Manual
- AdBlue Range
But you will receive the following messages when the Adblue levels reaches zero and prevents your car from getting started. In the case of these messages, mostly these are the NOX sensors in SCR system that causes these errors limiting your car to a number of miles driven before not being able to restart the engine.
- Engine Start Not Permitted (AdBlue Empty)
- Check AdBlue No engine Start Possible in XXX miles/km
- AdBlue system fault. No Restart in x km! See owner's manual
These errors will typically require replacement of faulty NOX sensor to enable the Adblue system back to the proper function.
It is very important that you respond to all the Adblue error messages without delay but before that let’s check in the detail, what is Adblue, how does it work, why it is used, why this error message occurs and how we can fix this error?
What is Adblue and how does it work?
Adblue is an advanced emission control technology which injects a liquid reducing agent via a special catalyst in the exhaust stream of an engine. It is also known as Diesel Exhaust Fluid (DEF), which is when released; creates a chemical reaction decomposing and converting 90% of harmful nitrogen oxide into harmless nitrogen, water and carbon dioxide before its ejection from the exhaust tailpipe of the vehicle.
Diagnosing “No Engine start possible error” trouble code
If accurately defined Adblue DEF injected into the exhaust to maintain exhaust temperature within acceptable parameters and promote optimum NOX filtration is at the required level, it will provide a high engine performance as well as economy on fuel budget; but if the system detects any inefficiency in the catalyst, a OBD code P20EE will be stored in PCM which reads as “SCR NOX Catalyst Efficiency below Threshold Bank 1 Issue” and means that Adblue system has come across of a malfunctioning component such as NOX sensor.
When a P20EE is stored in a diesel powered, OBD-II equipped vehicle, it means that the powertrain control module has detected that catalyst efficiency is below threshold for a certain engine bank. This particular code applies to the downstream catalytic converter (or NOX trap) for engine bank one.
You can perform a SCR NOX diagnosis with Star Diagnostic Scanner and check the following to find the possible fault codes.
- Values from NOX sensor control unit upstream of SCR catalytic converter
- Values from NOX sensor control unit downstream of SCR catalytic converter
Most commonly, this issue arises due to the faulty NOX sensors. Damaged wiring of NOX probe or the control unit of NOX sensor itself may trigger this issue.
Symptoms
If you notice any of the following symptoms, there are most likely the chances of NOX sensors failure.
- Reduction in fuel efficiency
- Excessive black smoke from vehicle exhaust
- Diminished engine performance
- Other SCR related codes
How to fix the error
Replacement of a faulty NOX sensor is the first thing that should be done without any delay after a diagnostic run as any holdup will lower the level of Adblue down to the zero and limit the count of the miles you car can be driven. Once it reaches to the Zero level, it won’t let you start the car as well as you car will no more remain law compliant on the roads.
So, to fix this error immediately within reasonable cost and convenience, you can buy a repair kit only for the probe only or a whole sensor including control unit to fix this error. Fixing P20EE DTC diagnostic trouble code and restoring your vehicle in its ideal condition is possible with the replacement of NOX probe or whole sensors. This is very rare that it doesn’t work but in most all cases it is successful so the diagnostic test should be ended with this replacement.
However, after replacement of NOX sensor, OBD codes needs to be cleared from the SCR system with the help of an OBD-II scanner. You can attempt to clear the codes at home or you can’t take it to any workshop or the dealer near you.
