P0204 on Mercedes-Benz: Causes, Symptoms and Fix Cost
Quick Answer
Safe to drive (short-term)
P0204 on a Mercedes-Benz is the injector circuit code for cylinder 4: the engine computer measured an open, a short or an unexpected resistance in that injector's wiring. On an inline four-cylinder, cylinder 4 is the end cylinder next to the gearbox, and a three-cylinder engine cannot set this code at all. A connector or wiring fix usually costs about 65-220 EUR at a workshop; a petrol injector fitted about 100-310 EUR.
- Severity
- Moderate · Fuel System
- Typical repair cost, all makes
- €5-€650
Connect a standard OBD2 adapter (Bluetooth LE on iPhone) to your Mercedes-Benz and Skanyx tells you what P0204 means on that engine, whether it is safe to keep driving, and what the fix should cost. Free on iPhone and Android.
Get Skanyx freeWhat does P0204 mean on a Mercedes-Benz?
The Quick Answer above is the generic definition. What follows is the model-specific detail for the Mercedes-Benz models that log P0204.
Mercedes C-Class
2007-2024
On OM651 and other CDI diesels the common-rail injectors are expensive and each carries a calibration code that must be written into the ECU after replacement, a job for XENTRY or a workshop. Petrol M274/M264 engines can throw P0204 from a corroded connector or chafed harness. Skanyx reads the circuit code and freeze frame but not the injector calibration data.
What causes P0204 on a Mercedes-Benz?
Beyond the generic causes listed on the main P0204 page, these are the patterns noted for Mercedes-Benz models:
Costly common-rail injector with calibration coding on OM651 CDI diesel
: Mercedes C-Class
Connector corrosion or harness chafe on M274/M264 petrol
: Mercedes C-Class
How to diagnose P0204 on a Mercedes-Benz with OBD2
- Use Skanyx to read P0204 with its freeze frame and list the other codes stored: P0304 (cylinder 4 misfire), P0270 or P0271 (cylinder 4 injector circuit low or high) and any lean code for the bank concerned
- Locate cylinder 4. On an inline four-cylinder it is the last cylinder, at the flywheel and gearbox end (at the pulley end on Peugeot and Citroen engines, which traditionally number the other way). On a V6 it is on bank 2 under both common numbering schemes. On BMW's N52 inline-six it is the first cylinder of the group the engine computer treats as bank 2
- Check the cylinder 4 injector plug and the last stretch of harness running to it. At the gearbox end the loom is clipped close to the engine, so look for chafing at clips and brackets as well as corrosion in the plug
- Measure the injector coil at its pins with the ignition off, then from the ECU pin for injector 4 to include the wiring. Compare both readings with the value for your engine
- If the injector and the wiring both measure correctly, have the injector signal checked with a noid light on port injection, or with an oscilloscope on direct-injection and diesel engines, whose injectors run at high voltage
- Swap injector 4 with injector 3, clear the code and drive. A code that moves to P0203 points to the injector; P0204 returning points to the wiring or the ECU
- A replacement common-rail diesel injector has to be coded to the cylinder 4 position with its correction code, which generic OBD2 cannot do. Budget for a brand tool such as Carly, OBDeleven or XENTRY, or have a workshop do it
How much does P0204 cost to fix on a Mercedes-Benz? (EUR)
Estimated repair costs for P0204 in EUR, compiled across makes. Expect Mercedes-Benz parts and labour towards the upper end of each range.
| Repair | Parts Cost | Labor Cost | Total Estimate | DIY Difficulty |
|---|---|---|---|---|
| Repair the cylinder 4 connector or wiring at home (DIY) | €5–€30 | €0–€0 | €5–€30 | Moderate |
| Workshop repair of the cylinder 4 injector circuit | €5–€40 | €60–€180 | €65–€220 | Professional |
| New cylinder 4 injector, petrol, workshop fitted | €40–€150 | €60–€160 | €100–€310 | Moderate |
| New cylinder 4 injector, common-rail diesel, workshop fitted and coded | €150–€400 | €100–€250 | €250–€650 | Professional |
Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.
Codes related to P0204
These codes are often seen alongside P0204 or point to related issues, on any make:
Looking for the full P0204 reference (all makes, full diagnosis flow, complete repair cost matrix)? See the main P0204 guide