Mercedes W204 and W205 C-Class: the fault list by generation

The W204 ran from 2007 to 2014 and the W205 from 2014 to 2021. They share a badge and very little else, and their fault lists differ accordingly.

Shared reference: Mercedes C and E-Class OBD diagnostics and Mercedes-Benz common DTC codes.

W204: the items to check

Balance shaft, on early M272 and M273 petrol engines

A documented concern on specific early production of the V6 and V8 petrol engines, affecting the balance shaft gear.

It is production-date specific, and later engines are unaffected. On an early V6 it is worth establishing whether the engine falls into the affected range.

Symptoms: a rattle, and correlation codes: P0016 crankshaft-camshaft correlation and P0017 to P0019 on bank 2.

Camshaft adjuster magnets

Fail and leak, producing variable valve timing faults: P0010 and P0013 camshaft actuator circuit and P2088 and P2089 camshaft actuator circuit low.

The OM651 diesel

Injectors and the rear-mounted timing chain: Mercedes OM651 diesel diagnostics.

Steering lock module

A documented failure on the W204 where the electronic steering lock does not release, and the car will not start. It is an expensive module and a well-known item.

The tell: nothing happens on starting, sometimes with a message about the steering lock: car won’t start: immobiliser troubleshooting.

Rear suspension bushes

Wear early relative to the rest of the car, producing knocks and geometry drift: suspension bushes wear symptoms and inner edge tyre wear.

W205: a different set

Direct injection carbon

All the petrol engines use direct injection, so intake valve deposits accumulate over time: GDI carbon buildup.

Electronics density

The W205 introduced substantially more electronics — driver assistance, more comfort modules, more networking.

Consequence: greater sensitivity to battery condition. A marginal battery produces communication codes across systems with no mechanical relationship, and it looks like multiple failures.

P0560 to P0563 system voltage faults, U0073 control module bus off and when the scanner lies about ghost codes.

Battery replacement generally needs registering. Fitting one without doing so leaves the charging strategy wrong: battery replacement and registration.

Driver assistance and calibration

Camera and radar based, and requiring calibration after windscreen or bumper work.

A screen replaced without calibration leaves a system that appears to work and does not aim where the software believes it does.

ADAS calibration and windscreen chip repair vs replacement.

Air suspension, where fitted

Airmatic on equipped cars. The failure sequence is predictable: bags perish, the compressor works harder, then fails.

The tell: the car sitting low after standing overnight. Fixing the leak first is dramatically cheaper than replacing a compressor that failed because of it.

Common to both

The 9G-Tronic and 7G-Tronic gearboxes are generally durable, and complaints usually trace to fluid condition or adaptation values rather than mechanical wear.

P0700 transmission control system malfunction and automatic transmission ATF diagnostics — P0894 transmission component slipping is the code that precedes the expensive conversation.

Water ingress through blocked drains, reaching modules under the carpets: damp carpet and electrical faults.

What generic OBD-II reaches: codes, live data, freeze frame and readiness. Comfort modules, driver assistance and coding need enhanced access: scan tool limits and manufacturer coding: VAG, BMW, Mercedes.

Buying used

1. Establish the generation and engine.
2. On an early W204 V6, check whether the balance shaft concern applies to that production date.
3. Read injector correction values on an OM651.
4. Cold-start it yourself.
5. Load-test the battery and check resting voltage after standing.
6. Ask about ADAS calibration on a W205 with any front-end work.
7. Leave it overnight and check ride height if it has air suspension.
8. Check readiness and permanent codes for a recent clear.

Try it on the free tier of the app — pair an ELM327 adapter and check resting voltage after an overnight stand. On a module-dense Mercedes, that single number explains a surprising share of what gets called unreliability.