MajorCommonEngine

Mercedes-Benz GLS: X166 OM642 BlueTEC AdBlue (SCR) Tank Heater, Heated Line and NOx Sensor Faults (GL350 / GLS350d)

X166 OM642 BlueTEC AdBlue (SCR) Tank Heater, Heated Line and NOx Sensor Faults (GL350 / GLS350d) is a common engine fault on the Mercedes-Benz GLS on the 2013–2019 cars, and we rate it major. Putting it right costs $700 to $4,500 at New Zealand independent workshop rates. Below is what goes wrong, the symptoms to notice on a test drive, where to look, and what to ask the seller before you hand over any money. It is one of 10 documented faults on the Mercedes-Benz GLS.

Vehicle: Mercedes-Benz GLS
Engine: 3.0L
Years: 2013–2019
Fuel: diesel
System: Engine

This page covers the Mercedes-Benz GLS as a model. Some faults only affect particular engines or build years — enter a plate below to narrow the list to one car.

All Mercedes-Benz GLS faults10 documented faults on this model

What you are looking at

No photograph available

We do not hold a verified photograph for this fault yet. We would rather show none than show a picture of something else.

What goes wrong

The X166 GL350 BlueTEC and GLS350d use the OM642 3.0 V6 diesel with an AdBlue (urea) SCR system to cut NOx. The heating element in the AdBlue tank drifts in resistance and fails (Mercedes bulletin LI49.20-P-056353 names model 166 with engine 642), the heated AdBlue delivery line can break internally, and the NOx sensors in the exhaust fail with age and heat. Any of these puts on the engine light and starts an AdBlue countdown that ends in a no-start after a set distance, and topping up AdBlue does not clear it. Parts must be coded and the SCR system re-initialised with a Mercedes-level scan tool after repair. There is no recall or extended warranty for this in NZ or AU.

What you would notice

Engine warning light on
AdBlue or 'Check AdBlue' message on the dash
'No start in X km' or 'Remaining starts' countdown
Message stays after AdBlue is topped up
Reduced power in some cases

How to check it

Where to look. AdBlue tank and heater under the rear of the car, heated AdBlue line along the underbody, NOx sensors in the exhaust before and after the SCR catalyst

Turn the key to ignition on and check every warning light goes out once the engine is running. Scroll through the dash messages with the steering wheel buttons and look for any AdBlue, 'no start in' or remaining-starts message, and check the AdBlue range readout. Open the AdBlue filler and look for heavy white crystals, which point to leaks or overfilling. Ask whether the AdBlue warning has ever come on and whether a NOx sensor, AdBlue heater, AdBlue line or tank has been replaced, and ask for invoices. Be wary if the seller has 'just cleared a light'. If a workshop inspection is possible: have a Mercedes specialist scan the engine (CDI) and SCR control units for stored codes such as 20BE1B, 20BD1B, P20F5, P2BA9, P13DF00 or P2BAA, check both NOx sensor readings, and check the AdBlue countdown counter.

What it costs to put right

$700 to $4,500 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

Ask the seller

“Has the AdBlue or engine warning light ever come on?”
“Has a NOx sensor, AdBlue heater, AdBlue line or tank ever been replaced?”
“Has the car ever shown a 'no start in' countdown?”
“Where do you buy your AdBlue and how often do you top it up?”

Now check the Mercedes-Benz GLS you are actually looking at

Everything above is true of the model, and it is free. What it does not tell you is whether THIS car has been looked after: its odometer history and whether the reading has ever gone backwards, whether there is still money owing on it, whether it has been reported stolen, how many owners it has had and what it is really worth today. That comes from the official records for that plate. Enter the plate for the free details, or get the full history and a market valuation from $13.49.

Not sure what you would be paying for? See what a full KickTyres check includes.

Where this comes from

The failure described above is documented in the sources below. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them.

Mercedes-Benz TSB LI49.20-P-056353 'Heating element of AdBlue tank has malfunction, fault code 20BE1B and/or 20BD1B' (validity model 166 with engine 642, NHTSA MC-10135857)
MBWorld Diesel Forum thread 912528 'P20F5 P2BA9' (2016 GL350 BlueTEC, broken heated AdBlue line)
Hella TechWorld: NOx sensor Mercedes-Benz diagnostic information ('AdBlue no start in 800 km' warning)
Mercedes-Benz TSB LI14.40-N-060049 SCR AdBlue warning strategy (initialisation after NOx sensor replacement)

Mercedes-Benz GLS buyer questions

Is x166 om642 bluetec adblue (scr) tank heater, heated line and nox sensor faults (gl350 / gls350d) serious on a Mercedes-Benz GLS?

We rate it major and common on the Mercedes-Benz GLS. The X166 GL350 BlueTEC and GLS350d use the OM642 3.0 V6 diesel with an AdBlue (urea) SCR system to cut NOx. The heating element in the AdBlue tank drifts in resistance and fails (Mercedes bulletin LI49.20-P-056353 names model 166 with engine 642), the heated AdBlue delivery line can break internally, and the NOx sensors in the exhaust fail with age and heat. Any of these puts on the engine light and starts an AdBlue countdown that ends in a no-start after a set distance, and topping up AdBlue does not clear it. Parts must be coded and the SCR system re-initialised with a Mercedes-level scan tool after repair. There is no recall or extended warranty for this in NZ or AU.

How much does it cost to fix on a Mercedes-Benz GLS?

$700 to $4,500 at New Zealand independent workshop rates. That figure is for this job on its own. A car showing the symptoms on this page is usually worth either walking away from or negotiating down by at least the repair figure.

Which Mercedes-Benz GLS years are affected?

Our research records this fault on the 2013–2019 Mercedes-Benz GLS. Build dates move around, especially on imported cars, so treat the range as the years to look hardest at rather than a guarantee either way. The official records tell you the exact build and first registration date for the car in front of you.