P20EE00 Code: Complete DIY Repair Guide

The P20EE00 code is a diagnostic trouble code (DTC) related to the Selective Catalytic Reduction (SCR) system in diesel engines. This code indicates that the SCR NOx (nitrogen oxides) catalyst efficiency is below the threshold for Bank 1. When this code is triggered, it means the vehicle’s emissions control system is not functioning as efficiently as it should, potentially leading to increased NOx emissions.

Faulty NOx Sensors

NOx sensors play a crucial role in monitoring the efficiency of the SCR system. When these sensors malfunction, they can provide inaccurate readings, leading to the P20EE00 code.

Symptoms:

• Check Engine Light (CEL) illumination
• Reduced fuel efficiency
• Possible decrease in engine performance

Technical Explanation:
NOx sensors measure the levels of nitrogen oxides in the exhaust before and after the SCR catalyst. The engine control module (ECM) uses these readings to determine the efficiency of the NOx reduction process. If the sensors provide incorrect data, the ECM may falsely detect low catalyst efficiency.

Step-by-step Diagnosis:

1. Connect an OBD-II scanner and verify the P20EE00 code.
2. Check for any additional codes that might be related to the NOx sensors or SCR system.
3. Use a diagnostic tool to view live data from both upstream and downstream NOx sensors.
4. Compare the readings between the sensors and against known good values.
5. Inspect the wiring and connectors for any signs of damage or corrosion.
6. Perform a voltage check on the sensor circuits to ensure proper power and ground.

Solution Methods:

• Clean the sensors if they are covered in soot or other debris.
• Replace faulty NOx sensors if cleaning doesn’t resolve the issue.
• Repair any damaged wiring or connectors.

Cost Estimate:
NOx sensor replacement can cost between $200 to $500 per sensor, including parts and labor.

Warning: Always use high-quality OEM or equivalent NOx sensors to ensure proper functionality and avoid recurring issues.

Contaminated or Low-Quality DEF

Diesel Exhaust Fluid (DEF) is crucial for the proper functioning of the SCR system. Contaminated or poor-quality DEF can lead to inefficient NOx reduction and trigger the P20EE00 code.

Symptoms:

• Illuminated check engine light
• Reduced engine power (limp mode)
• Decreased fuel economy

Technical Explanation:
DEF is a solution of urea and deionized water that is injected into the exhaust stream to convert NOx into harmless nitrogen and water. If the DEF is contaminated or of low quality, this chemical reaction may not occur efficiently, leading to higher NOx levels in the exhaust.

Step-by-step Diagnosis:

1. Check the DEF level and top up if necessary.
2. Inspect the DEF for any signs of contamination (e.g., discoloration, particles).
3. Verify the DEF quality using a refractometer or DEF quality tester.
4. Check the DEF tank and lines for any signs of corrosion or debris.
5. Review the vehicle’s maintenance history to ensure that only high-quality DEF has been used.

Solution Methods:

• Drain and flush the DEF system if contamination is suspected.
• Refill the system with fresh, high-quality DEF.
• Clean or replace the DEF filter if applicable.
• If persistent issues occur, consider replacing the DEF tank and lines.

Cost Estimate:
DEF system cleaning and refill can cost between $100 to $300. A complete system replacement could range from $500 to $1500, depending on the vehicle model.

Recommendation: Always use API-certified DEF and avoid storing DEF for extended periods to maintain its quality.

Clogged or Malfunctioning DEF Injector

The DEF injector is responsible for spraying the correct amount of DEF into the exhaust stream. A clogged or malfunctioning injector can lead to inadequate DEF delivery and trigger the P20EE00 code.

Symptoms:

• Increased NOx emissions
• Poor fuel economy
• Possible rough idle or hesitation

Technical Explanation:
The DEF injector must precisely meter and atomize the DEF for optimal NOx reduction. If the injector is clogged or not functioning correctly, it may not deliver the correct amount of DEF, leading to inefficient SCR catalyst operation.

Step-by-step Diagnosis:

1. Use a scan tool to check for any DEF injector-related codes.
2. Perform a visual inspection of the DEF injector and surrounding area for signs of leaks or crystallization.
3. Remove the DEF injector and inspect for clogs or damage.
4. Use a specialized DEF injector tester to verify proper spray pattern and flow rate.
5. Check the electrical connections and wiring to the injector for any damage or corrosion.

Solution Methods:

• Clean the DEF injector using specialized cleaning equipment.
• Replace the DEF injector if cleaning doesn’t resolve the issue.
• Repair or replace any damaged wiring or connectors.
• Perform a system relearn or adaptation procedure after replacement.

Cost Estimate:
DEF injector replacement can cost between $300 to $800, including parts and labor.

Warning: Never attempt to clean a DEF injector with compressed air, as this can damage the delicate components inside.

Exhaust Leaks

Exhaust leaks can introduce additional oxygen into the system, affecting NOx sensor readings and SCR catalyst efficiency, potentially triggering the P20EE00 code.

Symptoms:

• Loud exhaust noise
• Decreased engine performance
• Possible burning smell from the engine bay

Technical Explanation:
Exhaust leaks can allow unmetered air to enter the exhaust system, diluting the exhaust gases and affecting the NOx concentration. This can lead to inaccurate NOx sensor readings and reduced SCR catalyst efficiency.

Step-by-step Diagnosis:

1. Perform a visual inspection of the entire exhaust system, including manifolds, pipes, and connections.
2. Listen for any unusual exhaust noises, especially ticking or hissing sounds.
3. Use a smoke machine to pressurize the exhaust system and look for escaping smoke.
4. Check for any signs of soot or discoloration around potential leak areas.
5. Inspect exhaust gaskets and flex joints for signs of failure.

Solution Methods:

• Tighten any loose exhaust connections.
• Replace damaged exhaust gaskets or flex pipes.
• Repair or replace sections of the exhaust system that have rusted through.
• In severe cases, consider replacing the entire exhaust system.

Cost Estimate:
Minor exhaust repairs can cost between $100 to $400. A complete exhaust system replacement could range from $500 to $2000 or more, depending on the vehicle model.

Recommendation: Always use high-quality exhaust components and gaskets to ensure a proper seal and longevity.

Damaged SCR Catalyst

A damaged or degraded SCR catalyst can directly lead to reduced NOx conversion efficiency and trigger the P20EE00 code.

Symptoms:

• Decreased fuel economy
• Possible loss of engine power
• Increased exhaust emissions

Technical Explanation:
The SCR catalyst contains precious metals that facilitate the chemical reaction between NOx and DEF. Over time, or due to contamination, the catalyst can become less effective, leading to reduced NOx conversion and increased emissions.

Step-by-step Diagnosis:

1. Perform a visual inspection of the SCR catalyst for any external damage.
2. Use a scan tool to monitor the upstream and downstream NOx sensor values during operation.
3. Conduct a back pressure test to check for any blockages in the catalyst.
4. If possible, use an endoscope to inspect the internal structure of the catalyst.
5. Check for any signs of coolant or oil contamination in the exhaust system.

Solution Methods:

• In some cases, performing a forced regeneration may help restore catalyst efficiency.
• Clean the catalyst using specialized cleaning solutions if contamination is present.
• Replace the SCR catalyst if damage or degradation is severe.
• Address any underlying issues that may have led to catalyst damage (e.g., oil consumption, coolant leaks).

Cost Estimate:
SCR catalyst replacement can be expensive, ranging from $1000 to $3000 or more, depending on the vehicle model and labor costs.

Warning: Never attempt to remove or modify the SCR catalyst, as this is illegal and can lead to severe engine damage and increased emissions.

In conclusion, the P20EE00 code indicates a problem with the SCR system’s efficiency in reducing NOx emissions. While some causes can be addressed through simple maintenance or component replacement, others may require more extensive repairs. Always start with a thorough diagnosis to pinpoint the exact cause before attempting any repairs. If you’re unsure about any step in the diagnostic or repair process, it’s best to consult with a professional diesel technician who has experience with SCR systems.

Frequently Asked Questions About P20EE00

• Can I continue driving with the P20EE00 code?
  While you may be able to drive for a short distance, it’s not recommended to continue driving with this code. Prolonged operation can lead to reduced performance, increased emissions, and potential damage to other components.
• How often should I replace my DEF fluid?
  DEF fluid should be replenished as needed, typically every 3,000 to 4,000 miles for most vehicles. Always check your vehicle’s owner manual for specific recommendations.
• Can extreme temperatures affect the SCR system and cause the P20EE00 code?
  Yes, extreme cold can cause DEF to freeze, while extreme heat can degrade DEF quality. Both situations can potentially lead to SCR system inefficiency and trigger the P20EE00 code.
• Is the P20EE00 code covered under emissions warranty?
  In many cases, components related to the SCR system are covered under the vehicle’s emissions warranty. Check your warranty documentation or consult with your dealer for specific coverage details.
• Can using low-quality diesel fuel contribute to the P20EE00 code?
  While not directly related, using low-quality diesel fuel can lead to increased soot production and potential clogging of the SCR system, which may indirectly contribute to triggering the P20EE00 code.
• How long does it take to diagnose and repair a P20EE00 code issue?
  Diagnosis can take 1-2 hours, while repair time varies depending on the cause. Simple fixes like replacing a sensor might take an hour, while more complex repairs like catalyst replacement can take several hours.
• Will the P20EE00 code clear itself?
  In some cases, if the issue was temporary, the code might clear after several drive cycles. However, if the underlying problem persists, the code will likely return.
• Can I use water instead of DEF in an emergency?
  Never use water or any other liquid as a substitute for DEF. Doing so can cause severe damage to the SCR system and potentially to the engine. Always use proper DEF fluid.