AutoCodes – GMC – P021B GMC

P021B GMC Code - Cylinder 8 Injection Timing

Quick Answer

The Engine Control Module (ECM) has the ability to learn injector timing performance. Common causes include Faulty Fuel Injector 8, Fuel Injector 8 harness is open or shorted, Fuel Injector 8 circuit poor electrical connection. 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: P021B GMC indicates Cylinder 8 Injection Timing.
Common causes: Common causes include Faulty Fuel Injector 8, Fuel Injector 8 harness is open or shorted, Fuel Injector 8 circuit poor electrical connection.
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 341

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 Mar 22, 2024

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P021B GMC Description

The Engine Control Module (ECM) has the ability to learn injector timing performance. When the engine is at operating temperature, throttle closed and in deceleration fuel cut-off mode, the ECM will pulse each injector individually and measure the changes in rotational speed of the crankshaft using the input from the crankshaft position sensor. The ECM will run this diagnostic at one fuel rail pressure operating point for each injector. The ECM stores the injector timing value. The Diagnostic Trouble Code (DTC) will be set when the time to build up sufficient current to open the injector is below or above a predetermined threshold.

OBDII Code P021B GMC - Cylinder 8 Injection Timing - AutoCodes.com — P021B GMC Code - Cylinder 8 Injection Timing

What does this mean?

What are the Possible Causes of the DTC P021B GMC?

Faulty Fuel Injector 8
Fuel Injector 8 harness is open or shorted
Fuel Injector 8 circuit poor electrical connection
Faulty Engine Control Module (ECM)

How to Fix the DTC P021B GMC?

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 P021B GMC 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 P021B GMC code?

Need more information on how to fix the P021B GMC code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P021B GMC code diagnosed by a professional: Find a repair shop in your area

Information for Specific GMC Models

P021B 2014 GMC Sierra — Cylinder 8 Injection Timing
P021B 2015 GMC Sierra — Cylinder 8 Injection Timing
P021B 2016 GMC Sierra — Cylinder 8 Injection Timing
P021B 2017 GMC Sierra — Cylinder 8 Injection Timing
P021B 2018 GMC Sierra — Cylinder 8 Injection Timing

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 P021B GMC Code

1. What does the OBDII code P021B mean on a GMC?

The P021B code indicates an issue with the injection timing for cylinder 8, meaning the fuel injection is not occurring at the correct time.

2. What are common symptoms of the P021B code on a GMC?

Symptoms may include rough idling, engine misfire, reduced fuel efficiency, poor acceleration, and, in some cases, the Check Engine Light turning on.

3. What causes the P021B code to appear on a GMC?

Common causes include a faulty fuel injector, wiring issues in the injector circuit, a malfunctioning Engine Control Module (ECM), or debris clogging the fuel injector.

4. Can I drive my GMC with a P021B code?

Driving with this code is not recommended, as it can lead to further engine damage, reduced performance, and increased emissions.

5. How is the P021B code diagnosed on a GMC?

A mechanic will use a scan tool to confirm the code, inspect the injector wiring and connections, test the fuel injector, and possibly check the ECM for faults.

6. What repairs can fix the P021B code on a GMC?

Repairs may include replacing the faulty fuel injector, repairing or replacing damaged wiring, cleaning the injector, or reprogramming or replacing the ECM.

7. How much does it cost to fix the P021B code on a GMC?

Repair costs vary but typically range from $200 to $600, depending on whether the issue is with the injector, wiring, or ECM.

8. Can a dirty fuel injector cause the P021B code on a GMC?

Yes, a clogged or dirty fuel injector can disrupt injection timing and trigger the P021B code.

9. Will resetting the ECM clear the P021B code on a GMC?

Resetting the ECM may temporarily clear the code, but the underlying issue must be repaired to prevent the code from returning.

10. How can I prevent the P021B code from occurring on my GMC?

Regular maintenance, such as using high-quality fuel, cleaning injectors, and inspecting wiring, can help prevent injection timing issues.

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