7 speed limp mode

[Trustmeimadoctor]

Seems the car is stuck in limp mode no lights etc but stuck in second it's a w203 320 diesel

Any ideas?

[steve-V8s]

Does your car have a dpf ? My 204 did that when the differential pressure sensor failed. You need to get a code reader plugged in and look at the live data. The fault on mine was intermittant and the actual fault codes were hopeless.

[donkmeister]

Have you had any work done recently? On a previous car (not Mercedes, mind) the garage had forgotten to tighten the clip on the turbo pipe going into the inlet manifold, therefore when I got 20 miles up the road and reached a place I could boot it, the turbo pipe blew off and the engine and gearbox both went into limp-home mode (locked in 6th gear on that model).

Also, on the W211 7g (may be the same on yours), the gearbox control unit is mounted underneath the spot where cup-holders are fitted - liquids can drip onto the TCU and cause failures. Have you had any such spillages?

[Trustmeimadoctor]

Nope and nope BUT seems to have cured it's self now. It doesn't feel right tho I'm gonna have to get it in for a fluid change I think see what it's like after that

[anonymous-user]

Trustmeimadoctor said:

Nope and nope BUT seems to have cured it's self now. It doesn't feel right tho I'm gonna have to get it in for a fluid change I think see what it's like after that

Get the engine and transmissions codes pulled on a decent diagnostic code reader (ideally a star) before spending any money.

Old fluid is unlikely to cause limp mode.

I'd personally guess (and it is a guess as a few things can cause limp mode) an issue with the conductor plate/control unit within the transmission. The speed sensors are known to fail and bring on limp mode or total loss of drive, however its common for them to fail in only select circumstances, meaning with a cycle of the ignition, the car might run for hundreds of miles without any further issues.

The codes don't usually shown within the ECM, hence no EML and generic code readers often not able to detect a problem.