AutoCodes – GMC – P1056 GMC

P1056 GMC Code - Reductant Pump Low Speed

Quick Answer

The reductant pump motor is controlled by the reductant control module. Common causes include Faulty Reductant Pump and Sensor Assembly, Reductant Pump and Sensor Assembly harness is open or shorted, Reductant Pump and Sensor Assembly 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: P1056 GMC indicates Reductant Pump Low Speed.
Common causes: Common causes include Faulty Reductant Pump and Sensor Assembly, Reductant Pump and Sensor Assembly harness is open or shorted, Reductant Pump and Sensor Assembly 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 570

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 Jul 24, 2021

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P1056 GMC Description

The reductant pump motor is controlled by the reductant control module. The Engine Control Module (ECM) sends a command to the reductant control module via a direct wire connection. This command is converted by the reductant control module into the desired pump speed The ECM checks the state of the wire to the reductant control module for circuit continuity. The signal sent by the ECM to the reductant control module is diagnosed for open circuit, short circuit to ground, and short circuit to voltage. The Diagnostic Trouble Code (DTC) will be set when the reductant control module detects that the reductant pump rotor is stalled for greater than 5 s.

OBDII Code P1056 GMC - Reductant Pump Low Speed - AutoCodes.com — P1056 GMC Code - Reductant Pump Low Speed

What does this mean?

What are the Possible Causes of the DTC P1056 GMC?

Faulty Reductant Pump and Sensor Assembly
Reductant Pump and Sensor Assembly harness is open or shorted
Reductant Pump and Sensor Assembly circuit poor electrical connection
Faulty Reductant Control Module

How to Fix the DTC P1056 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 P1056 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.

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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 P1056 GMC Code

1. What does the OBDII code P1056 mean on a GMC?

P1056 indicates "Reductant Pump Low Speed," which means the reductant (DEF) pump is not operating at the expected speed, potentially affecting the SCR (Selective Catalytic Reduction) system.

2. What are the common symptoms of the P1056 code in a GMC vehicle?

Symptoms may include a check engine light, DEF system warning messages, reduced engine performance, or the vehicle entering a limited power mode.

3. What causes the P1056 code to appear on a GMC?

Common causes include a faulty reductant pump, electrical issues like damaged wiring or connectors, a clogged DEF filter, or a failed reductant control module.

4. Can I drive my GMC with a P1056 code?

While you may be able to drive the vehicle, prolonged use with this code can lead to reduced engine performance or emissions compliance issues. It's best to address it promptly.

5. How is the P1056 code diagnosed in a GMC?

A technician will use a scan tool to confirm the code, inspect the reductant pump, check wiring and connectors for damage, and test the system's operation.

6. How do I fix the P1056 code on my GMC?

Repairs may involve replacing the reductant pump, repairing damaged wiring or connectors, cleaning the DEF system, or reprogramming the reductant control module.

7. Can a clogged DEF filter cause the P1056 code?

Yes, a clogged DEF filter can restrict the flow of reductant, potentially causing the pump to operate at low speed and trigger the P1056 code.

8. What tools are needed to troubleshoot the P1056 code on a GMC?

A diagnostic scan tool, a multimeter for electrical testing, and tools to access and inspect the reductant pump and DEF system are typically required.

9. Is the P1056 code covered under warranty for my GMC?

This depends on your warranty coverage and vehicle age. Emissions-related components, such as the reductant system, may be covered under the emissions warranty.

10. Can low-quality DEF cause the P1056 code on a GMC?

Yes, using poor-quality or contaminated DEF can lead to system malfunctions, including reductant pump performance issues that may trigger the P1056 code.