The OBD-II fault code P20E8 is a diagnostic trouble code that can surface in diesel vehicles equipped with Selective Catalytic Reduction (SCR) systems. This code specifically points to an issue within the AdBlue or Diesel Exhaust Fluid (DEF) system, indicating “Reductant Pressure Too Low.” Understanding and addressing this fault promptly is crucial for maintaining your vehicle’s emissions system and overall performance.
Understanding the P20E8 Code and Your AdBlue System
The P20E8 error code signals that the pressure in your AdBlue system is not within the expected range. The SCR system relies on the precise injection of AdBlue into the exhaust stream to reduce harmful NOx emissions. A pump is responsible for delivering this fluid from the tank to the injector at a specific pressure, typically between 5 and 6.5 bar when the engine is running in many systems. When the pressure falls below this threshold, the P20E8 code is triggered, alerting you to a potential malfunction.
Potential Causes of the P20E8 Fault
Several factors can lead to insufficient urea pressure in the AdBlue system. Pinpointing the exact cause is the first step towards effective repair. The most common culprits include:
- Inefficient AdBlue Pump: The pump itself might be failing to generate adequate pressure. This could be due to wear and tear, internal damage, or electrical issues preventing it from operating at its optimal capacity. In some cases, the pump and control unit are integrated, requiring replacement of the entire assembly.
- Pressure Line Cracks or Leaks: The lines carrying AdBlue from the pump to the injector can develop cracks or leaks over time due to vibration, temperature fluctuations, or physical damage. A leak in the pressure line will inevitably lead to a drop in pressure, triggering the P20E8 code.
- Urea Injector Issues: A poorly sealed or malfunctioning urea injector can also contribute to low pressure in the system. If the injector is leaking or not operating correctly, it can disrupt the pressure balance and cause the fault code to appear.
Diagnosing the P20E8 Fault Code
To accurately diagnose the P20E8 fault, a systematic approach is necessary. A practical diagnostic procedure to discriminate the root cause involves measuring the AdBlue flow rate. This test helps determine if the issue lies with the pump’s delivery capacity or further down the line with the injector or piping.
Here’s a step-by-step guide to perform this diagnostic test:
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Disconnect the Urea Tubing: Carefully disconnect the AdBlue tubing from the injector.
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Prepare a Graduated Container: Position a graduated container to collect the discharged AdBlue fluid.
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Initiate the Flow Test: Activate the AdBlue pump system (often through a diagnostic function in professional scan tools) to discharge fluid into the container for a precise time, approximately four minutes.
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Measure the Collected Fluid: After four minutes, or when the procedure is complete, measure the volume of AdBlue collected in the container.
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Analyze the Results:
- Insufficient Flow (Less than 40ml): If you collect significantly less than the expected 50 ± 10 ml (e.g., below 40ml), this indicates a problem with the pump’s ability to deliver the correct amount of fluid or a blockage/leak in the feed pipe.
- Correct Flow (Around 50ml): If the collected volume is within the expected range (40-60ml), it suggests that the pump and feed line are functioning correctly. In this case, the issue is likely with the urea injector itself.
Alt text: Close-up of a diesel AdBlue injector, a key component in the SCR system that can cause P20E8 fault code if malfunctioning.
Resolving the P20E8 Fault
Based on the diagnostic test results, you can proceed with targeted repairs:
- If the flow test indicates insufficient pump delivery: The AdBlue pump or the integrated pump/control unit is likely the culprit and may require replacement. Inspect the feed pipe for any blockages or damage as well.
- If the flow test shows correct pump delivery: Focus your attention on the urea injector. It should be inspected for proper function and sealing. Replacement of the injector might be necessary to resolve the P20E8 fault code.
Addressing the P20E8 fault code promptly is essential for ensuring your diesel vehicle operates efficiently and complies with emission standards. Utilizing diagnostic tools, like those offered by Autel, can significantly streamline the troubleshooting process, allowing for accurate identification and resolution of issues within the AdBlue system.
