AutoCodes – Generic – P21B2

P21B2 Code - Excessive Time To Enter Closed Loop NOx Absorber Control

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: P21B2 indicates Excessive Time To Enter Closed Loop NOx Absorber Control.
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 700

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 P21B2 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, during post fuel injection, the O2 Sensor 1/1 value is above a calibrated threshold a fail count is recorded as incremented. If not, it is recorded as decremented. After a calibrated number of total counts (incremented and decremented), the counter value is above a calibrated value, a fault is set.

OBDII Code P21B2 - Excessive Time To Enter Closed Loop NOx Absorber Control - AutoCodes.com — P21B2 Code - Excessive Time To Enter Closed Loop NOx Absorber Control

What does this mean?

What are the Possible Causes of the DTC P21B2?

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 P21B2?

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 P21B2 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 P21B2 code?

Need more information on how to fix the P21B2 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P21B2 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

P21B2 Dodge — Excessive Time To Enter Closed Loop NOx Absorber Control
P21B2 RAM — Excessive Time To Enter Closed Loop NOx Absorber Control

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 P21B2 Code

1. What does the OBDII code P21B2 mean?

P21B2 indicates that the vehicle's engine control module (ECM) has detected an excessive delay in transitioning to closed-loop NOx absorber control during emissions management.

2. What are the common symptoms of code P21B2?

Symptoms may include an illuminated check engine light, reduced fuel efficiency, increased emissions, and potential performance issues like hesitation or rough idling.

3. What causes the P21B2 code to appear?

The code can be triggered by a malfunctioning NOx sensor, issues with the NOx absorber catalyst, faulty oxygen sensors, or exhaust leaks upstream of the catalytic converter.

4. Can a dirty or clogged NOx absorber cause code P21B2?

Yes, a clogged or degraded NOx absorber can prevent the system from entering closed-loop control in a timely manner, triggering the code.

5. Is code P21B2 safe to drive with?

While the vehicle may still be drivable, ignoring this code can lead to increased emissions, reduced fuel economy, and potential damage to the NOx absorber or other exhaust components over time.

6. How is code P21B2 diagnosed?

A technician will use a scan tool to monitor the NOx sensor and oxygen sensor data, inspect the NOx absorber system, and check for exhaust leaks or wiring issues.

7. What repairs can fix the P21B2 code?

Repairs may include replacing a faulty NOx sensor, oxygen sensor, or NOx absorber, repairing exhaust leaks, or updating the ECM software if necessary.

8. Can a software update resolve the P21B2 code?

In some cases, a software update for the ECM may address incorrect parameters or delays in NOx absorber control, resolving the code.

9. How much does it cost to fix code P21B2?

The cost varies depending on the issue but can range from $100 for sensor replacement to $1,000 or more for NOx absorber replacement or extensive repairs.

10. Can regular maintenance help prevent code P21B2?

Yes, regular maintenance such as timely oil changes, monitoring emissions components, and addressing exhaust leaks promptly can help prevent this code.