AHI Module Issues: Understanding DTC P24F700

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If you are an owner or mechanic working with a Volvo D13 truck, you may encounter issues with the AHI module. One of the most common issues is the DTC P24F700 code, which is related to the aftertreatment fuel system. This issue can cause the regeneration process to fail, leading to increased downtime and potential damage to the engine.

Fortunately, there are several troubleshooting steps that you can follow to diagnose and fix the issue. In this guide, we will outline some of the common causes of DTC P24F700 and provide tips on how to resolve the problem.

What is AHI System?

The Aftertreatment Hydrocarbon Injector (AHI) System is a component of the Emissions Aftertreatment System (EATS) that monitors and controls fuel injection into the Diesel Oxidation Catalyst (DOC) to regenerate the Diesel Particulate Filter (DPF). The system is made up of 3 primary components: The AHI Module, Fuel and Air Lines, and the AHI Nozzle (7 Injector).

AHI Module Component Overview

The AHI Module for model year 2017 and newer trucks is mounted to the fuel filter housing. In older vehicles, it was mounted to the side of the engine block. Despite the different configuration, the functionality is the same and the module’s primary job is to control the amount of fuel and air to the nozzle.

There are 3 primary failure modes of the AHI Module (Dosing Block):

  • Contaminated Air Supply
  • Contaminated Fuel Supply
  • Electrical Circuit Fault

Any AHI Module failure from air or fuel is primarily due to system contamination. The AHI module is susceptible to debris and oil from the upstream systems. It is imperative that when replacing the AHI Module that the fuel and air system are adequately evaluated.

Diagnosis and Repair

Perform a DTC Readout using Premium Tech Tool. Use the below fault tables to aid in diagnosing AHI system and the root cause of the failure.

  • ONLY Active codes or codes with DTC Status showing as “Confirmed” should be diagnosed.
  • If there are no Active or Status Confirmed DTCs and the vehicle will not successfully complete a regen, proceed to the AHI Nozzle Evaluation section.

Air And Fuel Supply Faults

DTC Fault Description System To Evaluate
P24F700 Exhaust Aftertreatment Fuel Air Purge Valve Stuck Closed 1. Air Supply
2. AHI Module
3. Fuel/Air Lines between AHI Module and Nozzle
P24F600 Exhaust Aftertreatment Fuel Air Purge Valve Stuck Open 1. Air Supply
2. AHI Module
3. Replace the AHI Nozzle and clean Fuel/Air Line
P20DC00 Exhaust Aftertreatment Fuel Supply Control Stuck Closed 1. Fuel Supply
2. If no problem with fuel supply, follow PTT Diagnostics
P20CF7A Exhaust Aftertreatment Fuel Injector “A” Stuck Open 1. Fuel Supply
2. AHI Module
P20D000 Exhaust Aftertreatment Fuel Injector “A” Stuck Closed 1. AHI Module
2. Replace the AHI Nozzle and clean Fuel/Air Line
P20DE00 Exhaust Aftertreatment Fuel Pressure Sensor Circuit Range/Performance Follow PTT Diagnostics for this fault.
Suspected Failure:
– AHI Pressure Sensor
– Air Supply
– AHI Nozzle or Air/Fuel Lines

What is DTC P24F700?

DTC P24F700 is a diagnostic trouble code that indicates a fault in the engine control module (ECM) of a diesel engine equipped with an aftertreatment system. This code is specific to General Motors (GM) diesel engines, and it is related to the selective catalytic reduction (SCR) system, which is designed to reduce harmful emissions from the engine.

When the ECM detects a fault in the SCR system, it will set the P24F700 code and illuminate the check engine light. This code indicates that the ECM has detected an issue with the system that is preventing it from properly reducing emissions.

Possible Causes of DTC P24F700

  1. Exhaust Aftertreatment Fuel Air Purge Valve Stuck Closed

One of the most common causes of DTC P24F700 is a stuck-closed exhaust aftertreatment fuel air purge valve. This valve is responsible for purging excess fuel from the aftertreatment system during the regeneration process. If it becomes stuck, it can prevent the fuel from being purged, leading to a failed regeneration process.

  1. Low Air Pressure

Low air pressure can also cause issues with the AHI module, leading to a failed regeneration process. If the air pressure is below the recommended level, the system may not be able to provide enough air to the AHI module, causing it to malfunction.

  1. Faulty Parts

Other faulty parts can also cause issues with the AHI module, including the hydrocarbon doser, temperature sensors, and exhaust ducts. If any of these parts are damaged or malfunctioning, they can prevent the regeneration process from completing successfully.

AHI Module Evaluation

  1. Perform PTT Operation 2545-08-03-02 Exhaust aftertreatment diagnostics option D. Follow the results of the operation.
  2. If the AHI Module or Nozzle is replaced it is imperative to follow guidance on use/reuse of the fuel/air supple line. See the Fuel & Air Line Section Below.

Rules for Replacement

Warranty will only cover replacement of the AHI Module if one of the fault codes in the Yellow sections above is active or confirmed. If the AHI Module is suspected to have failed with no codes present, an eService case is required for further evaluation.

In addition, if the AHI module is being replaced. Maintenance records will be required showing the fuel filters and air dryer/filter have been properly maintained and are not the root cause of the failure.

The Air dryer / filters and Fuel Filters are all consumables. These components will be denied on a warranty claim unless they have been properly maintained. Refer to Service At a Glance (SAG) found in the Trucks Dealer Portal under the Information tab – Service – Service literature for replacement guides.

Standard Diagnostic Time for AHI Module is 1.5 hours.

Read also: DD15 Coolant System: Diagram, Issues, and Maintenance Tips

Troubleshooting Steps

  1. Check Battery Cell and Air Dryer

The first step in troubleshooting DTC P24F700 is to check the battery cell and air dryer. Ensure that each cell in the battery is working correctly and that the air dryer is free from any issues that may prevent it from functioning correctly.

  1. Inspect Air Pressure and Regulator

Next, inspect the air pressure and regulator, ensuring that the system is providing enough air to the AHI module. If the regulator is malfunctioning, replace it with a new one to ensure that the system is working correctly.

  1. Verify Fuel Pressure

Check the fuel pressure on the AHI module at the sensor to ensure that it is at the correct level. If the pressure is low, the system may not be able to provide enough fuel to complete the regeneration process.

  1. Check for Leaks

Inspect the exhaust ducts and temperature sensors for any leaks or issues that may prevent the system from functioning correctly. Replace any damaged parts to ensure that the system is working correctly.

Conclusion

If you encounter issues with the AHI module on your Volvo D13 truck, DTC P24F700 is a common problem that you may encounter. Fortunately, by following the troubleshooting steps outlined in this guide, you can diagnose and resolve the issue quickly and efficiently, reducing downtime and preventing potential damage to the engine. Remember to perform regular maintenance on your truck to ensure that the AHI module and other components are working correctly, reducing the risk of future issues.

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