Used Mercedes GL350 BlueTEC and ML350 BlueTEC: What to Know

A used Mercedes GL 350 BlueTEC or ML 350 BlueTEC appeals to drivers who cover long highway miles and want a big, comfortable SUV with strong low-end torque. These 3.0-liter V6 diesels were built for relaxed cruising, and the GL adds a third row for families.

They also come with responsibilities a gas SUV doesn't have: diesel exhaust fluid (AdBlue/DEF) refills, a more complex emissions system, and an emissions settlement history you need to verify. If you're shopping in Irvine or elsewhere in Orange County, this guide explains what's different about BlueTEC ownership in California and what to check before buying.

GL 350 vs. ML 350 BlueTEC

We list both: a 2015 Mercedes-Benz GL 350 BlueTEC 4MATIC with 114,156 miles and a 2014 Mercedes-Benz ML 350 BlueTEC 4MATIC with 92,041 miles. See each listing for current price and equipment.

AdBlue (DEF): how it works and why it matters

BlueTEC diesels use AdBlue, also called diesel exhaust fluid (DEF), to reduce nitrogen oxide emissions. It's stored in its own tank and needs periodic refilling, separate from fuel.

What you need to know:

• Low DEF triggers warnings. The car alerts you as the level drops.
• Ignore it, and the car limits starts. If DEF runs out, the system eventually restricts restarting the engine until you refill.
• Use the right fluid. Buy DEF that meets the required specification; it's widely sold at auto parts stores and many truck stops.
• DEF system faults can trigger warnings and need diagnosis. Have the system scanned during an inspection.

When you test-drive, check the DEF level and any related messages in the instrument cluster.

The emissions settlement and modification

In 2020, Daimler and Mercedes-Benz settled with the U.S. EPA and the California Air Resources Board over emissions on certain 2009–2016 BlueTEC diesel vehicles. As part of that, an approved emissions modification was made available for affected vehicles.

Both the 2015 GL 350 and 2014 ML 350 fall within that model-year range. Before buying any BlueTEC from those years:

1. Ask a Mercedes-Benz dealer to check by VIN whether the approved emissions modification was performed.
2. Get that confirmation in writing if possible.
3. Check for open recalls at nhtsa.gov/recalls.

Confirming the fix protects you at future smog checks and avoids surprises.

Smog checks for diesels in California

Diesel rules differ from gas in a few ways:

• Diesels from 1998 and newer with a GVWR of 14,000 lb or less need smog checks in California. That includes both of these SUVs.
• Biennial renewal: Orange County requires smog checks at renewal; these model years are past their first eight model years.
• At transfer, the seller must provide a valid smog certificate, good for 90 days. Every car we sell is smog checked before sale.

Our article on diesel smog checks in California covers the details, and BAR's station locator is at bar.ca.gov if your notice requires a STAR station.

Inspection checklist for a used BlueTEC

Have a shop familiar with Mercedes diesels inspect the vehicle. Ask them to:

• Scan all modules for stored codes, especially emissions, DEF and engine management.
• Check the emissions system components, including sensors and the diesel particulate filter, for faults.
• Inspect for leaks around the engine, oil cooler area, transmission and differentials.
• Test cold-start behavior. Diesels rely on glow plugs; a rough or slow cold start can point to issues.
• Check the suspension, including air suspension if equipped, for even ride height and no warnings.
• Review the 7-speed automatic for smooth shifts.
• Review service records for oil changes with the correct diesel-rated oil and timely maintenance.

Our vehicle history and inspection guide explains how to combine the CARFAX with an independent inspection.

Is a diesel right for how you drive in Orange County?

Diesels tend to be happiest on longer drives where the engine and emissions system reach full temperature. If most of your driving is short hops around Irvine, such as school drop-offs and errands under a few miles, a diesel's emissions system may not get the extended running it prefers. If you regularly drive I-5 to San Diego, the 15 toward Las Vegas, or long commutes into Los Angeles, a BlueTEC's highway manners make more sense.

Other practical points:

• Fuel availability: fewer stations sell diesel than gasoline; note where you'd fill up.
• Towing: both models were used for towing; if a car has a hitch, ask what it pulled.
• Insurance: get a quote by VIN first.

Frequently asked questions

What is AdBlue on a Mercedes BlueTEC?

AdBlue is Mercedes' name for diesel exhaust fluid (DEF), which the BlueTEC system uses to reduce NOx emissions. It's stored in a separate tank and needs regular refills; if it runs out, the car will eventually limit restarting.

How do I know if the emissions fix was done on a used BlueTEC?

Ask a Mercedes-Benz dealer to check by VIN whether the approved emissions modification from the 2020 EPA and CARB settlement was performed. Get written confirmation if you can.

Do ML 350 BlueTEC problems make it a risky buy?

Any older diesel SUV can need costly emissions or sensor repairs, and we don't publish reliability scores. A complete service history, confirmed emissions modification and a diesel-savvy inspection reduce the risk considerably.

Does a diesel SUV need a smog check in Orange County?

Yes. Diesels from 1998 and newer with a GVWR of 14,000 lb or less need smog checks at biennial renewal and at transfer when required.

Is the GL 350 a good three-row SUV?

It's a roomy, comfortable three-row option for long trips. Compare it with gas alternatives in our used three-row SUV guide.

See them in Irvine

Our hub on the best used SUVs and trucks in Orange County puts these diesels alongside gas options. Browse our Irvine used car listings, ask for the CARFAX, and call or text (516) 835-6141 to set up a test drive in Irvine.