How Serious Is Code P204B?
Code P204B is a serious code that should be addressed promptly. If ignored, it can lead to:
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Disabling of the SCR system (selective catalytic reduction), which is essential for reducing pollutant emissions.
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Catalyst damage if the issue persists, resulting in costly repairs.
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Increased pollution with excessive black smoke emissions.
Prompt intervention is therefore necessary to avoid mechanical complications and failures in emissions testing.
Symptoms of Code P204B
Common signs associated with this code include:
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🚨 Check engine light on (or SCR warning message).
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⛽ Decreased fuel efficiency (increased fuel consumption).
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⚡ Reduced engine performance (lack of power, unstable idle).
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💨 Excessive black smoke from the exhaust.
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🔍 Other SCR system-related codes (such as P20EE, P2047, etc.).
Possible Causes of Code P204B
Several factors can trigger this fault:
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Faulty reductant pressure sensor – Incorrect data sent to the PCM.
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Electrical issues – Cut wires, short circuits, or corroded connectors in the sensor circuit.
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SCR/PCM module failure – Programming error or internal malfunction.
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Mechanical problem in the SCR system – Faulty reductant pump, clogged injector, or insufficient AdBlue level.
Diagnostic Procedure for Code P204B
Required tools:
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📟 OBD2 scanner (to read codes and real-time data).
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🔌 Multimeter (DVOM) (to test circuits and sensors).
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📖 Vehicle-specific repair manual (wiring diagrams, reference values).
Troubleshooting steps:
1. Checking codes and real-time data
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Connect the scanner and note all stored codes.
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Check live data (SCR pressure, sensor performance).
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Look for relevant technical service bulletins (TSB) for the model.
2. Testing the reductant pressure sensor
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Using the multimeter, check the sensor’s resistance and voltage according to manufacturer specifications.
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If values are out of range, replace the sensor.
3. Inspecting electrical circuits
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Check connectors and wiring between the sensor and PCM.
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Look for broken wires, short circuits, or corrosion.
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Test continuity with the multimeter (disconnected from PCM to avoid damage).
4. Checking the SCR system
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Verify the level and quality of AdBlue (urea solution).
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Inspect the SCR pump and injector for blockages or leaks.
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If necessary, perform cleaning or replacement of faulty components.
Conclusion
Code P204B indicates a critical issue in the SCR system, which can lead to excessive pollution and catalyst damage. An electrical and mechanical inspection is required to identify the source of the problem (sensor, wiring, or SCR module).
🔧 Tip: If diagnosis is complex, consult an SCR system specialist to avoid incorrect repairs.
⚠ Ignoring this code may result in higher repair costs and failure of the emissions control system.
Need help? Share your symptoms in the comments for targeted advice!