What is an AHI Dosing Module on Volvo / Mack engines? (3-minute read)

Essential Takeaways

• The AHI module’s purpose is to regulate and control the amount of fuel that goes to the 7^th injector during the DPF regeneration process.
• The AHI module goes through various self-checks during the operation of the engine. If the system detects an issue, it will automatically cause an active fault code related to the AHI module or 7^th injector. 
• If you have a failed AHI module, passive, active, and forced DPF regens will all fail.
• You cannot bypass the AHI module to do a forced regen. The truck requires all of the emission components to be in proper working order for the truck to start a forced regen. You can use OTR Diagnostics to get you out of a derate situation by resetting the AFT system.

It is important to know where everything is located. Reference the picture below as you read through the blog post for a better visual.

AHI Dosing System Module = Aftertreatment injection shut off Valve

What does an AHI module do?
The AHI module’s purpose is to regulate and control the amount of fuel that goes to the 7th injector during the DPF regeneration process. The AHI module has a low-pressure fuel and high-pressure fuel that is controlled by the internals of the AHI module. The Engine Management Unit or EECU control the AHI module.

The AHI module has two electrical connections on this component. One of them controls the actual operation of the module, and the other connection is a fuel pressure sensor that measures the pressure going to the 7th injector.

What happens when the AHI module fails?
The AHI module goes through various self-checks during the operation of the engine. If the system detects an issue, it will automatically cause an active fault code related to the AHI module or 7th injector. The fault code will sometimes lead you to believe that the problem is with the 7th injector; however, in reality, there is an issue with the AHI module.

*Example Fault
MID 128 PPID 328 FMI 7
MID 128 PPID 329 FMI 7
SA 0 SPN 3471 FMI 7
SA 0 SPN 5443 FMI 7
SA 16 P113000
SA 0 SPN 3490 FMI 7 

*Overview
Aftertreatment injection shutoff valve, Aftertreatment 1 hydrocarbon dosing system.

*Troubleshooting
FMI 7: Module has detected an incorrect response from a mechanical system. This usually leads to a fault component.

*Description
Aftertreatment injector stuck closed.

*Fault Symptoms
Malfunction indicator lamp illuminated. Yellow Check lamp illuminated. Active, Passive, or Forced Regeneration not possible.

*Repair Procedure
Faulty fuel lines. Aftertreatment hydrocarbon Doser obstructed and or dirty. Faulty Aftertreatment hydrocarbon dosing module. Shut off valve stuck closed.
*Courtesy of truckfaults.com

What causes the AHI module to fail?
The regenerations system relies heavily on the AHI module to perform its function. The AHI module is always performing and always checking itself to make sure it can drive fuel to the 7th injector for the regeneration process to complete.

Will the truck start a DPF regen with a failed AHI module?
No! The regen system will fault out when the AHI module has an active fault code. This will cause a HIGH SOOT condition and passive, active, and forced regens will all fail.

Can you bypass this AHI module to do a forced regen?
No, you cannot bypass the AHI module to do a forced regen. The truck requires all of the emission components to be in proper working order for the truck to start a forced regen. You can read and clear the codes with OTR Diagnostics, but the fault codes will come active as soon as the truck performs a self-check on the AHI module and will cause the forced regen to fail. 

Where is the AHI located on a Volvo D11 D13 D16 Mack MP7 MP8 MP10?
The location of this module is on the driver's side of the engine. It is located underneath the starter on the rear side of the fuel filter housing. You can see it very faintly, but it’s attached to the block with a couple of electrical connections attached to it.

Do you have to take the truck into the shop to replace the AHI module?
We always recommend a certified diesel technician to perform repairs on the emission system because you are dealing directly with fuel and with higher pressures when it’s injecting into the 7th injector. However, if you are technically and mechanically inclined, you may be able to perform this yourself. A video will be coming soon from OTR on how to replace this yourself!

Is the AHI module a common part to fail?
The AHI module commonly fails if you have a truck between the years 2007-2016 US07 US10 US13 Emissions. Since there are various small ports inside the AHI module, the components and/or passages inside get worn out and cause problems with not performing per manufacturer specifications. This will cause fault codes that cause a severe derate.

*Warning* Some OEM modules come failed from the parts counter. These parts are called DOE (Dead on Arrival), so make sure you have a warranty when you purchase in case this happens to you.

Until next time! 👋
Stay safe, stay healthy & be blessed.