AutoCodes – Generic – P20EF

P20EF Code - SCR NOx Pre-Catalyst Efficiency Below Threshold Bank 1

Quick Answer

The Selective Catalyst Reduction (SCR) catalyst is monitored to ensure it is capable of NOx conversion. Common causes include Faulty NOx Sensor, Diesel Exhaust Fluid, Faulty Selective Catalyst Reduction (SCR) Catalyst. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P20EF indicates SCR NOx Pre-Catalyst Efficiency Below Threshold Bank 1.
Common causes: Common causes include Faulty NOx Sensor, Diesel Exhaust Fluid, Faulty Selective Catalyst Reduction (SCR) Catalyst.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 7,203

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Jun 14, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
Comments
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Code P20EF Description

The Selective Catalyst Reduction (SCR) catalyst is monitored to ensure it is capable of NOx conversion. The concentration of NOx upstream of the SCR is calculated based on a model. NOx concentration downstream of the SCR is measured with a NOx sensor. Using these concentrations, the cumulative efficiency of the SCR catalyst is calculated and compared to a threshold. If the cumulative efficiency is below this threshold for a sufficient period of time, a fault will be indicated.
The reductant, Diesel Exhaust Fluid (DEF), which is used as part of the SCR catalyst reaction, is monitored to ensure the tank is not refilled with an improper reductant. Upon detection of a refill event, the monitor is activated. After the SCR Catalyst Efficiency Monitor has completed and the SCR has been determined to be functional, the efficiency monitor continues to calculate the cumulative efficiency of the system. Each subsequent value for cumulative efficiency is included in two filtering routines, one for short term efficiency and the other for long term efficiency. If the difference between the two filtered efficiencies becomes greater than a threshold, a fault is indicated. the short term efficiency needs to be less than 0.20 and the delta between short and long term efficiency needs to be greater than 0.10.

OBDII Code P20EF - SCR NOx Pre-Catalyst Efficiency Below Threshold Bank 1 - AutoCodes.com — P20EF Code - SCR NOx Pre-Catalyst Efficiency Below Threshold Bank 1

What does this mean?

What are the Possible Causes of the DTC P20EF?

Faulty NOx Sensor
Diesel Exhaust Fluid
Faulty Selective Catalyst Reduction (SCR) Catalyst

How to Fix the DTC P20EF?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P20EF code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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Information for Specific Makes

P20EF Dodge — SCR NOx Pre-Catalyst Efficiency Below Threshold Bank 1
P20EF Ford — SCR NOx Pre-Catalyst Efficiency Below Threshold Bank 1

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.