Severity of Code P204E
Level: Critical 🔴
- Immediate Impact: The SCR (Selective Catalytic Reduction) system may be deactivated, leading to increased pollutant emissions (NOx) and a risk of catalyst failure.
- Long-term Risks:
- Damage to the SCR catalyst (high replacement cost: €1,000 to €3,000).
- Overloading of the particulate filter (DPF) due to an unbalanced air-fuel mixture.
- The vehicle may enter limp mode (power limitation, reduced speed).
Common Symptoms of P204E
- 🚨 Check Engine Light (MIL) or SCR warning light illuminated.
- 🔥 Black or bluish smoke from the exhaust (incomplete combustion).
- 📉 Decreased engine performance (slow acceleration, power loss).
- ⛽ Increased fuel consumption (up to 20%).
- ⚠️ Related Codes: P20EE, P204F, or P2201 (SCR/AdBlue® issues).
Main Causes of P204E
- Faulty Reducer Pressure Sensor:
- Incorrect signal due to internal failure or contamination by urea (DEF).
- Electrical Issues:
- Short circuit or open circuit in the sensor wiring.
- Oxidized or disconnected connectors (exposure to moisture).
- PCM/SCR Controller Failure:
- Outdated software or calibration error.
- Faulty Reducer Pump:
- Internal leak or insufficient pressure (related to AdBlue®).
- Other Causes:
- Low level or poor quality AdBlue®.
- Clogged or damaged SCR injector.
Detailed Diagnostic Procedure
Required Tools
- Advanced OBD2 scanner (e.g., Delphi, Autel).
- Digital multimeter (DVOM).
- Vehicle-specific technical documentation (wiring diagrams, test procedures).
Key Steps
- Check for TSBs (Technical Service Bulletins):
- Look for software updates or recalls related to the SCR system for your model.
- Code and Live Data Analysis:
- Use the scanner to:
- Read all stored codes (P204E + related codes).
- Monitor reducer pressure (compare to manufacturer specifications).
- Check SCR temperature and AdBlue® flow rate.
- Pressure Sensor Test:
- Measure the sensor’s resistance and voltage (reference: 0.5–4.5 V depending on pressure).
- Compare with factory values. If out of specifications ➔ replacement required.
- Electrical Circuit Inspection:
- Test for continuity and absence of short circuits between the sensor and PCM.
- Check the sensor’s power supply (+5V) and ground.
- SCR Pump and Injector Check:
- Test pump pressure with a pressure gauge (if applicable).
- Inspect the injector for crystalline deposits (clean with a specific kit).
- Repair Validation:
- Clear codes and perform a drive cycle to check for P204E reappearance.
Recommended Solutions
- Replacement of the pressure sensor: €150 to €400 (part + labor).
- Cleaning of AdBlue® circuits: Use a certified cleaning kit.
- PCM update: Contact a dealership for reprogramming.
- Replacement of the SCR pump: High cost (€800 to €2,000).
Important Considerations
- Use only ISO 22241 certified AdBlue® (non-compliant products damage the system).
- Avoid driving with code P204E: Risk of significant additional costs (e.g., SCR catalyst replacement).
This approach ensures accurate diagnosis and avoids unnecessary repairs. Always consult the manufacturer’s technical guides for exact specifications.