P20EE – SCR NOx Catalyst Efficiency Below Threshold

Understanding the P20EE Code: Causes, Diagnosis, and Repair

The P20EE code indicates that the Selective Catalytic Reduction (SCR) NOx catalyst efficiency is below the acceptable threshold for bank 1. This code is considered a severe issue, with a DTC severity of 3 out of 3, meaning you should stop and repair the vehicle immediately.

Urgency and Driving Considerations

When the P20EE code appears, it is crucial to address the issue promptly. Continuing to drive with this code active can lead to further damage to the emissions system and potentially cause the vehicle to enter a limp mode. It is strongly recommended to stop driving and have the vehicle diagnosed by a qualified mechanic or dealership as soon as possible.

Code Specificity and Affected Parts

The P20EE code is not specific to any particular make or model of vehicle. It is a generic code that applies to diesel vehicles equipped with an SCR system. The main components involved in this issue are:

• SCR Catalyst: Responsible for reducing NOx emissions in the exhaust system.
• NOx Sensors: Monitor the NOx levels before and after the SCR catalyst.
• Diesel Exhaust Fluid (DEF) System: Injects a urea solution into the exhaust stream to enable the SCR process.

Common Causes

Several factors can trigger the P20EE code, including:

1. Faulty NOx sensors
2. Clogged or damaged SCR catalyst
3. Insufficient or contaminated DEF
4. Leaks in the DEF system
5. Malfunctioning DEF injector

Diagnostic Steps

To properly diagnose the P20EE code, follow these steps:

1. Retrieve the fault code using an OBD-II scanner.
2. Check the DEF level and quality.
3. Inspect the DEF system for leaks or damage.
4. Test the NOx sensors for proper operation.
5. Evaluate the SCR catalyst efficiency using a diagnostic tool.

Repair Solutions

The repair solution for the P20EE code depends on the underlying cause. Common repairs include:

• Replacing faulty NOx sensors
• Cleaning or replacing the SCR catalyst
• Refilling or replacing contaminated DEF
• Repairing leaks in the DEF system
• Replacing the DEF injector

Prevention and Maintenance

To prevent the occurrence of the P20EE code, follow these maintenance practices:

• Regularly check and top off the DEF tank
• Use high-quality DEF that meets the manufacturer's specifications
• Adhere to the recommended service intervals for the SCR system
• Address any emissions-related issues promptly

Cost of Repair and Parts

The cost of repairing the P20EE code can vary depending on the specific issue and the vehicle make and model. Here are some estimated costs:

• NOx sensor replacement: $200 to $600 (€170 to €510)
• SCR catalyst replacement: $1,500 to $3,000 (€1,275 to €2,550)
• DEF injector replacement: $500 to $1,000 (€425 to €850)

Related Fault Codes

Other fault codes that may appear alongside the P20EE code include:

• P20EF (SCR NOx Pre-Catalyst Efficiency Below Threshold Bank 1)
• P2002 (Diesel Particulate Filter Efficiency Below Threshold)

Remember, proper diagnosis and repair by a qualified professional are essential to resolve the P20EE code and ensure the vehicle's emissions system is functioning correctly.

Frequently Asked Questions About P20EE Engine Code

What does the P20EE code mean?

The P20EE diagnostic trouble code indicates that the Selective Catalytic Reduction (SCR) system’s NOx catalyst efficiency is below the required threshold for bank 1. This means the SCR system is not adequately reducing nitrogen oxide emissions.

What are the symptoms of a P20EE code?

Common symptoms include:

• Illuminated check engine light
• Reduced fuel efficiency
• Decreased engine performance
• Strong smell of diesel exhaust

Is it safe to drive with a P20EE code?

While you may be able to drive cautiously for a short time, it’s best to diagnose and repair the underlying issue promptly to avoid further damage to the SCR system and prevent excessive emissions.

What causes the P20EE code to trigger?

Potential causes include:

• Faulty NOx sensor
• Clogged or defective diesel particulate filter
• Exhaust leaks before the SCR catalyst
• Contaminated diesel exhaust fluid (DEF)
• Malfunctioning DEF injector
• Wiring issues

How do you diagnose a P20EE code?

Key diagnostic steps are:

1. Scan for all codes and note freeze frame data.
2. Visually inspect SCR components and wiring.
3. Check DEF quality and level.
4. Test NOx sensors and SCR temperature sensor.
5. Verify DEF injector operation.
6. Pressure test exhaust system for leaks.

Can a bad DEF injector cause a P20EE code?

Yes, a clogged or malfunctioning DEF injector can prevent the proper dosing of diesel exhaust fluid into the exhaust stream, reducing the efficiency of the SCR catalyst.

How do you test NOx sensors?

Using a scan tool, compare the readings from the upstream and downstream NOx sensors. They should respond similarly under various operating conditions. Large discrepancies can indicate a faulty sensor.

What should the DEF tank level be?

The DEF tank should be kept at least 1/4 full to ensure an adequate supply of diesel exhaust fluid for the SCR system to function properly. Avoid running the tank empty.

Can contaminated DEF trigger a P20EE code?

Yes, using contaminated, expired, or diluted DEF can impair the SCR catalyst’s ability to convert nitrogen oxides, triggering a P20EE code.

What are some common P20EE repairs?

Depending on the root cause, repairs may include:

• Replacing a faulty NOx sensor
• Cleaning or replacing the DEF injector
• Repairing exhaust leaks
• Replacing the diesel particulate filter
• Reprogramming the ECM

How much does it cost to fix a P20EE code?

The cost can range from $100 for minor repairs to over $1500 for major components like the SCR catalyst. Diagnostic fees, parts, and labor can vary widely depending on the specific issue and repair shop.

Can a software update fix a P20EE code?

In some cases, a software reflash or ECM reprogramming may resolve a P20EE code if it’s caused by a glitch or outdated programming. However, it’s more commonly a hardware issue.

How often should the DEF filter be changed?

The DEF filter should be replaced according to the manufacturer’s recommended service interval, typically every 100,000-150,000 miles. A clogged filter can contribute to SCR system issues.

What is the normal operating temperature for the SCR system?

The ideal operating temperature for the SCR catalyst is typically between 570-750°F (300-400°C). The system may not function efficiently if the exhaust temperature is too low.

Can a P20EE code cause limp mode?

In some vehicles, a recurring P20EE code may trigger a failsafe or limp mode to protect the engine and emissions system from further damage until the issue is addressed.

How do you check for exhaust leaks?

Visually inspect the exhaust system from the turbocharger outlet to the tailpipe for signs of damage, corrosion, or loose connections. A smoke machine or leak detector can help pinpoint leaks.

What happens if you run out of DEF?

If the DEF tank runs empty, the SCR system will not function, leading to increased NOx emissions. The vehicle may enter a reduced power mode or refuse to restart until the tank is refilled.

Can a bad catalytic converter cause a P20EE code?

While a failing SCR catalyst can trigger a P20EE code, a conventional upstream catalytic converter is unlikely to be the direct cause. However, a clogged cat could cause exhaust backpressure issues.

How do you test DEF quality?

Use a DEF refractometer to check the urea concentration. It should be 32.5% urea by weight. Contaminated or diluted DEF will have a lower concentration and appear darker in color.

Can low coolant cause a P20EE code?

Low coolant is unlikely to directly trigger a P20EE code, but it can lead to overheating and other issues that may affect the SCR system. Always maintain proper coolant levels.