AutoCodes – RAM – P21B3 RAM

P21B3 RAM Code - Closed Loop NOx Absorber At Limit Too High

Quick Answer

When the engine runs in DeNOx mode, the Powertrain Control Module (PCM) monitors how much post-injection fuel has been injected. Common causes include Mass Air Flow (MAF) Sensor value not learned, EGR valve sticking or restricted, Thermostat outlet restricted. 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: P21B3 RAM indicates Closed Loop NOx Absorber At Limit Too High.
Common causes: Common causes include Mass Air Flow (MAF) Sensor value not learned, EGR valve sticking or restricted, Thermostat outlet restricted.
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 864

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 Aug 09, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P21B3 RAM Description

When the engine runs in DeNOx mode, the Powertrain Control Module (PCM) monitors how much post-injection fuel has been injected. Once it exceeds a threshold, the measured O2 Sensor 1/1 is supposed to be lower than a threshold. If after a sufficient amount of post fuel is injected, the O2 Sensor 1/1 value is still high for a calibrated time, the fail counter is incremented by 1. If it is not, it is decremented by 1. If the counter has been incremented or decremented for a calibrated number of times, and the counter value is greater than a calibrated value, this fault is set. The Diagnostic Trouble Code (DTC) will set if the time duration after an active soot regeneration is requested exceeds a calibrated threshold and the Diesel Oxidation Catalyst inlet temperature has not reached the light-off temperature threshold to begin closed-loop control.

OBDII Code P21B3 RAM - Closed Loop NOx Absorber At Limit Too High - AutoCodes.com — P21B3 RAM Code - Closed Loop NOx Absorber At Limit Too High

What does this mean?

What are the Possible Causes of the DTC P21B3 RAM?

Mass Air Flow (MAF) Sensor value not learned
EGR valve sticking or restricted
Thermostat outlet restricted
Faulty EGR cooler bypass control valve
Faulty EGR airflow control valve
Leaking or damaged NOx absorber catalyst

How to Fix the DTC P21B3 RAM?

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 P21B3 RAM 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.

Need more information about the P21B3 RAM code?

Need more information on how to fix the P21B3 RAM code? Get Access to Factory Service Manuals

Need Help with the Code?

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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.

Frequently Asked Questions about P21B3 RAM Code

1. What does the OBDII code P21B3 indicate?

The code P21B3 indicates that the Closed Loop NOx Absorber at Limit Too High, specifically related to the RAM system.

2. What are the common symptoms of the P21B3 code?

Common symptoms of the P21B3 code may include reduced engine performance, poor fuel efficiency, and in some cases, the illumination of the check engine light.

3. What can cause the P21B3 code to trigger?

The P21B3 code can be triggered by issues such as a malfunctioning NOx absorber, a faulty sensor, exhaust leaks, or a problem with the engine control module.

4. How serious is the P21B3 code?

The P21B3 code should be addressed promptly as it can lead to increased emissions, reduced engine efficiency, and potential damage to the catalytic converter or other emission control components.

5. How can I diagnose the P21B3 code?

Diagnosing the P21B3 code typically involves using an OBDII scanner to retrieve the code, conducting a visual inspection for leaks, testing the NOx absorber system, and checking sensor readings.

6. Can I continue driving with the P21B3 code present?

It is not recommended to continue driving with the P21B3 code present, as it can lead to further damage to emission control components and may result in the vehicle failing an emissions test.

7. How can I repair the P21B3 code?

Repairing the P21B3 code may involve replacing the NOx absorber, repairing any leaks in the exhaust system, replacing faulty sensors, or reprogramming the engine control module.

8. Is it possible to reset the P21B3 code without addressing the underlying issue?

While you can clear the code using an OBDII scanner, it is crucial to address the underlying issue causing the P21B3 code to prevent further problems down the line.

9. Can a DIY enthusiast fix the P21B3 code?

Depending on your skill level and access to tools, some DIY enthusiasts may be able to address the P21B3 code by replacing components like sensors or conducting basic diagnostic tests. However, more complex repairs may require professional assistance.

10. How can I prevent the P21B3 code from recurring?

Regular maintenance, such as timely replacement of the NOx absorber, checking for exhaust leaks, and monitoring sensor performance, can help prevent the recurrence of the P21B3 code.