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Mercedes-Benz ML-Class ML 420 CDI common faults.

2005–2008, SUV, diesel, 306 HP.

The fault list covers: OM629DE40LA engine, MB7229 transmission.

What you save stays on this device only. My saves

2 fault write-ups. Both are important. No recall on the list.

If you know the year, pick it. Faults for other years drop out of the list.

Before you buy

Known faults

2 important faults

7G-Tronic (722.9): mechatronics and conductor plate

expensive

In the Mercedes 7 speed 722.9 automatic (7G-Tronic / 7G-Tronic Plus) the mechatronics unit and the conductor plate (Leiterplatte) age over time: jerking on shifts, delayed engagement, a "Getriebe schützen" message, and fault codes on the gearbox electronics.

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The repair is typically replacing the mechatronics unit or the conductor plate together with an oil change: not the whole gearbox. The complaint is most common on the longitudinal platforms from around 2005 to 2015 (C/E/ML and the early GLC).

The 9G-Tronic (725.0) is a different design; this applies only to the 7G.

between 100,000 and 220,000 km

What to check

  • Try it cold and warm: a delayed 1 to 2 or 2 to 3 shift is suspect
  • Watch for the gearbox warning or the "Getriebe schützen" message on the dash
  • Ask for a fault code read on the gearbox controller (not just the engine codes)
1 more steps in the write-up

Airmatic air suspension: leaking air spring, overworked compressor

expensive

The Mercedes Airmatic system holds the ride height with air springs and electronically controlled dampers. The most common faults over time are the relay, the compressor and a leaking air spring or air line.

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The rear air springs of the 2003 to 2009 E-Class (W211) are particularly prone to leaking along the clamps. If the system leaks, the compressor runs continuously, overheats and fails, so an unrepaired leak takes the compressor with it.

Symptoms: one corner of the car sinks by morning, an "Air Suspension" or level control fault message, and compressor noise while standing. It was an option (or standard) across several generations from the W220 S-Class onwards; the estate E-Class often has air springs with level control on the rear axle as standard.

between 100,000 and 220,000 km

What to check

  • In the morning, before setting off, look at all four corners: an uneven stance means a suspected leak
  • With the car standing, listen to the compressor: continuous running indicates it is overworked
  • Ask for a fault code read on the suspension controller (level and pressure sensor codes of the C1132 / C1144 kind)
3 more steps in the write-up

Checklist

Mercedes-Benz ML-Class ML 420 CDI

First what you would check on any car. Then the faults of this model.

Before you buy

Checklist

The printed sheet starts with what you would check on any car. What you tick stays on this device only.

On every car

Ask the owner

Faults of this model

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Engine and transmission

OM629DE40LA

235 kW (320 HP) · diesel

MB7229 · 7G-Tronic / 7G-Tronic Plus, longitudinal (Mercedes 722.9 / NAG2)

automatic · 7 speed

Torque limit700 Nm
MakerMercedes-Benz

We built the code from the model and the gear count. The factory sheet does not state it.

Variant data

What is in this version

Factory data

Trim
ML 420 CDI
Body
SUV
Fuel
diesel
Transmission
automatic
Engine size
3996 cc
Power
225 kW (306 HP)
Drive
AWD
Production
2005–2008

Factory service interval

The manufacturer specifies this for this version. Of the mileage and the time, the one that comes first is the one that counts.

  • Air filter

    • 60,000 km or 4 years

  • Cabin (pollen) filter

    • 30,000 km or 2 years

  • Brake fluid change

    • first: 3 years, then 2 years(first change at 3 years, then every two years)

  • Fuel filter, diesel

    • 60,000 km or 2 years
All W164 versions

Information, not an expert opinion

We write the descriptions, and we put the source next to them. A person reviews them before they go out. They are still information, not a technical expert opinion.

  • A fault on the list does not mean the car you are looking at has it.
  • A fault missing from the list does not mean the model is fault-free. Write-ups are made model by model. Not all of them are done.
  • You decide whether to buy. This is no substitute for an inspection. That needs a workshop and a history check.
Details in the terms