The largest online repair guide library for every car

About us
Contact support
FAQ
Sign up
Sign in

2018 GLE 350d AdBlue Warning and Check Engine Light - SCR System Fault?

0

Mike T. · rep 0 · May 25, 3:08 AM · 1 replies · solved · Question

Vehicle: 2018 Mercedes-Benz GLE 350d (W166)

My 2018 Mercedes-Benz GLE 350d (W166) just popped up with an AdBlue warning message on the dash, saying "Engine start not possible in XXX miles." Shortly after, the check engine light came on. I topped up the AdBlue tank, but the warning hasn't gone away, and the countdown is still ticking down.

I'm worried about being stranded. Is this a common issue with these diesel models? What could be causing it, and is there anything I can check myself before taking it to the dealership? I've heard these systems can be complex and expensive to fix.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 3:08 AM

0

ClearTheCode admin answer:

AdBlue (Diesel Exhaust Fluid - DEF) system issues are unfortunately not uncommon on modern Mercedes-Benz diesel vehicles, including your 2018 GLE 350d (W166). The system is crucial for meeting emissions standards, and a fault can indeed lead to a non-start condition once the countdown reaches zero.

Here are common causes and steps:

  1. AdBlue Level Sensor Failure: Even if you've topped up, a faulty sensor might not register the correct fluid level, keeping the warning active. This is a very common failure point.
  2. DEF Heater Failure: The AdBlue fluid can freeze in cold temperatures, so a heater is integrated into the tank. If this fails, the system won't function correctly, especially in colder climates.
  3. NOx Sensors: These sensors monitor the exhaust gas before and after the Selective Catalytic Reduction (SCR) converter. If they fail, the system can't verify its effectiveness, triggering a fault. Common codes include P20EE (SCR NOx Catalyst Efficiency Below Threshold) or P2200/P2201 (NOx Sensor Circuit Malfunction).
  4. DEF Pump/Injector Malfunction: The pump delivers AdBlue to the injector, which sprays it into the exhaust. Clogs or failures in these components can prevent proper DEF delivery, leading to codes like P20B9 (Reductant Heater 'A' Control Circuit/Open) or P20F6 (Reductant Consumption Too Low).
  5. Wiring or Module Issues: Less common, but electrical faults can also occur.

When to See a Shop:

  • Immediate Professional Diagnosis: Given the 'engine start not possible' countdown, it's crucial to get this diagnosed by a Mercedes-Benz specialist or dealership as soon as possible. They have the specific diagnostic tools (XENTRY/DAS) required to read manufacturer-specific fault codes and properly test the individual components of the SCR system.
  • Avoid DIY Repairs: Due to the complexity and integration of the SCR system, DIY attempts beyond topping up the fluid are generally not recommended and could potentially lead to further issues or incorrect diagnosis. A professional can accurately pinpoint the failing component and replace it, often requiring software updates or adaptations after the repair.
Menu

Help & account