AutoCodes – RAM – P21B4 RAM

P21B4 RAM Code - NOx Absorber Over Temperature

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 Exhaust Temperature Sensors failed in-range low, Unintended fueling, Damaged NOx absorber 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: P21B4 RAM indicates NOx Absorber Over Temperature.
Common causes: Common causes include Exhaust Temperature Sensors failed in-range low, Unintended fueling, Damaged NOx absorber 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 463

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 P21B4 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 when the NAC outlet temperature exceeds a calibrated high threshold for a calibrated period of time.

OBDII Code P21B4 RAM - NOx Absorber Over Temperature - AutoCodes.com — P21B4 RAM Code - NOx Absorber Over Temperature

What does this mean?

What are the Possible Causes of the DTC P21B4 RAM?

Exhaust Temperature Sensors failed in-range low
Unintended fueling
Damaged NOx absorber catalyst

How to Fix the DTC P21B4 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 P21B4 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.

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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 P21B4 RAM Code

1. What are the common symptoms of OBDII code P21B4 RAM NOx Absorber Over Temperature?

Overheating of the NOx absorber, reduced engine performance, and illuminated check engine light are common symptoms.

2. What are the possible causes of the P21B4 code indicating NOx Absorber Over Temperature?

Causes may include a faulty NOx sensor, a malfunctioning NOx absorber, issues with the exhaust gas recirculation system, or a problem with the engine control module.

3. How serious is the P21B4 fault code related to NOx Absorber Over Temperature?

Ignoring this code can lead to increased emissions, reduced fuel efficiency, and potential damage to the catalytic converter or other emission control components.

4. Can driving with the P21B4 code present cause further damage to the vehicle?

Continued driving with the NOx absorber over temperature can potentially lead to more severe damage to the emission control system and may result in the vehicle failing an emissions test.

5. What should be the first step in diagnosing and repairing the P21B4 fault code?

The first step is to perform a thorough inspection of the NOx absorber, NOx sensor, and related components to identify any visible damage or issues.

6. Are there any DIY repair tips for fixing the P21B4 RAM NOx Absorber Over Temperature code?

DIY repairs are not recommended for this code due to the complexity of the emission control system. It's best to consult a professional mechanic for proper diagnosis and repair.

7. How much does it typically cost to repair the P21B4 fault code related to the NOx Absorber Over Temperature?

Repair costs can vary depending on the exact cause of the code, but it may involve replacing the NOx sensor, repairing the NOx absorber, or addressing issues with the exhaust system. Costs can range from a few hundred to over a thousand dollars.

8. Can resetting the check engine light resolve the P21B4 code temporarily?

Resetting the check engine light may temporarily clear the code, but if the underlying issue is not addressed, the code is likely to return.

9. How can I prevent the P21B4 RAM NOx Absorber Over Temperature code from reoccurring?

Regular maintenance, such as keeping the exhaust system clean and ensuring proper functioning of the emission control components, can help prevent the code from reoccurring.

10. Is it safe to continue driving the vehicle with the P21B4 code until it's repaired?

It is generally not recommended to continue driving with the P21B4 fault code present, as it can lead to further damage and potentially cause the vehicle to fail emissions tests.