MajorCommonTransmission

Mercedes-Benz CLS: 7G-Tronic Plus 722.9 conductor plate (transmission control unit) failure, stuck in limp mode

7G-Tronic Plus 722.9 conductor plate (transmission control unit) failure, stuck in limp mode is a common transmission fault on the Mercedes-Benz CLS on the 2011–2017 cars, and we rate it major. Putting it right costs $1,800 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 5 documented faults on the Mercedes-Benz CLS.

Vehicle: Mercedes-Benz CLS
Years: 2011–2017
Gearbox: auto
System: Transmission

This page covers the Mercedes-Benz CLS 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 CLS faults5 documented faults on this model

What you are looking at

No photograph available

We do not hold a verified photograph of the Mechatronic / valve body yet. We would rather show none than show a picture of a different part.

What goes wrong

Every CLS with the 7G-Tronic Plus 722.9 gearbox has its transmission control unit and speed sensors built onto a conductor plate inside the gearbox, sitting in hot fluid. The speed sensors (Y3/8n1, n2, n3) or the board fail, the gearbox loses its speed signals and drops into limp mode, holding 2nd gear (or no reverse) until the engine is restarted, and the fault usually gets more frequent until the plate is replaced and coded online to the car. Old fluid also wears the valve body, giving harsh or flared shifts. Some facelift diesels (2014 on) moved to the 9G-Tronic, which does not share this part.

What you would notice

Gearbox stuck in 2nd gear with a transmission warning, back to normal after a restart
Harsh or thumping downshifts coming to a stop
Flare or slip on the 2-3 or 3-4 change
Delayed engagement when selecting Drive or Reverse
Speedometer or cruise control dropping out at the same time as a shift fault

How to check it

Where to look. Inside the automatic gearbox, bolted to the valve body under the transmission sump pan

On the test drive, drive for at least 20 minutes so the gearbox is fully hot, as these faults often only appear warm. Accelerate gently from rest and count the shifts up to 7th, then slow to a stop and feel for thumps on the downshifts. Select Drive and Reverse with the car stationary and note any delay or clunk. Watch the dash for a transmission or limp message and check whether the car pulls away in 2nd only. Ask for proof of gearbox fluid and filter changes (Mercedes calls for this about every 60,000 to 125,000 km; many owners never do it). If a workshop inspection is possible: read the transmission control unit for stored codes such as 0717, 0718, 2767, 2768 or P0720, and check the 13-pin connector plug at the side of the gearbox for fluid wicking into the harness.

Parts involved: Mechatronic / valve body.

What it costs to put right

$1,800 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 gearbox ever gone into limp mode or shown a transmission warning?”
“When was the gearbox fluid and filter last changed?”
“Has the conductor plate or valve body ever been replaced?”

Now check the Mercedes-Benz CLS 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.

Circuit Board Medics: Mercedes-Benz 722.9 Conductor Plate TCM Failure Overview and Solution
MB Medic: 722.9 7G-Tronic Automatic Transmission Problems and Solutions
Go-Parts: P0720 on 2010-2016 Mercedes-Benz E-Class, Output Speed Sensor and Conductor Plate Fixes
MBWorld forum thread: 722.9 transmission fault, second time: valve body/conductor plate (control unit)?

Mercedes-Benz CLS buyer questions

Is 7g-tronic plus 722.9 conductor plate (transmission control unit) failure, stuck in limp mode serious on a Mercedes-Benz CLS?

We rate it major and common on the Mercedes-Benz CLS. Every CLS with the 7G-Tronic Plus 722.9 gearbox has its transmission control unit and speed sensors built onto a conductor plate inside the gearbox, sitting in hot fluid. The speed sensors (Y3/8n1, n2, n3) or the board fail, the gearbox loses its speed signals and drops into limp mode, holding 2nd gear (or no reverse) until the engine is restarted, and the fault usually gets more frequent until the plate is replaced and coded online to the car. Old fluid also wears the valve body, giving harsh or flared shifts. Some facelift diesels (2014 on) moved to the 9G-Tronic, which does not share this part.

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

$1,800 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 CLS years are affected?

Our research records this fault on the 2011–2017 Mercedes-Benz CLS. 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.