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P0203 on Mercedes-Benz: Causes, Symptoms and Fix Cost

Quick Answer

Safe to drive (short-term)

P0203 on a Mercedes-Benz tells you the engine computer found an electrical fault in the circuit of the cylinder 3 injector: open, shorted or outside its resistance limits. On a four-cylinder it is an inner cylinder next to cylinder 4, and on three-cylinder engines such as Ford's 1.0 EcoBoost it is the last cylinder in the row. Workshop wiring repairs cost about 65-220 EUR; 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 P0203 means on that engine, whether it is safe to keep driving, and what the fix should cost. Free on iPhone and Android.

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What does P0203 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 P0203.

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 P0203 from a corroded connector or chafed harness. Skanyx reads the circuit code and freeze frame but not the injector calibration data.

What causes P0203 on a Mercedes-Benz?

Beyond the generic causes listed on the main P0203 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 P0203 on a Mercedes-Benz with OBD2

  1. Read P0203 and the freeze frame with Skanyx. Note any P0303 (cylinder 3 misfire), P0267 or P0268 (cylinder 3 injector circuit low or high) and other injector codes stored at the same time
  2. Work out where cylinder 3 is. On a four-cylinder engine it is the third from the pulley end, next to cylinder 4 at the gearbox end. On a three-cylinder engine it is the last cylinder, at the gearbox end. On V6 and V8 engines cylinder 3 is on bank 1 whichever numbering the maker uses
  3. Inspect the cylinder 3 injector connector and the branch of harness feeding it. Look for a cracked latch, corrosion in the pins and insulation worn through where the loom is clipped to the engine
  4. If P0203 was stored together with another injector code, check the shared supply fuse, relay and ground first. Two injectors failing at the same moment is much less likely than a fault in something they share
  5. Measure the injector coil at its pins with the ignition off, then repeat from the ECU pin for injector 3 to include the harness. Use the specification for your engine type
  6. Swap injector 3 with a neighbour, cylinder 2 or 4 (cylinder 2 on a three-cylinder), clear the code and drive. If the code moves with the injector, replace it; if P0203 stays, repair the wiring or check the ECU driver
  7. When a direct-injection injector is removed, fit new PTFE combustion seals before refitting. On common-rail diesels the injector correction codes must match each cylinder, which needs a brand tool or a workshop

How much does P0203 cost to fix on a Mercedes-Benz? (EUR)

Estimated repair costs for P0203 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
DIY repair of the cylinder 3 connector or wiring €5–€30 €0–€0 €5–€30 Moderate
Cylinder 3 circuit traced and repaired at a workshop €5–€40 €60–€180 €65–€220 Professional
Cylinder 3 petrol injector replaced at a workshop €40–€150 €60–€160 €100–€310 Moderate
Cylinder 3 common-rail diesel injector replaced at a workshop €150–€400 €100–€250 €250–€650 Professional

Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.

These codes are often seen alongside P0203 or point to related issues, on any make:

Looking for the full P0203 reference (all makes, full diagnosis flow, complete repair cost matrix)? See the main P0203 guide

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