KC-2157

2/28/22, 8:47 AM
Article
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Aftertreatment Hydrocarbon Injector (AHI)
Troubleshooting Guide - US10+OBD13 And Newer
Emissions
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System Overview
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
(7th 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
UI
; Live
upstream systems. It is imperative that when replacing the AHI Module
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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
1. Follow PTT
Diagnostics for this
fault.
; Live UI
Suspected Failure:
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- AHI Pressure
Sensor
- Air Supply
- AHI Nozzle or
Air/Fuel Lines
Air System Evaluation
1. Replace the following components:
- Air Regulator
- Air Dryer Cartridge/Filter (A proper oil coalescing filter/cartridge
MUST be used)
2. Ensure the air tanks are properly drained
3. Clean the air supply line to the AHI module
Fuel System Evaluation
1. Replace the fuel filters with OEM or OEM approved parts
2. Visually check the fuel condition and ensure there is no debris or
contamination in the fuel tanks.
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.
Electrical Faults
DTC
Fault Description
P269A00
Exhaust Aftertreatment Fuel
Injector "A" Circuit High
P269900
Exhaust Aftertreatment Fuel
Injector "A" Circuit Low
; Live UI
P269713
Action
Exhaust Aftertreatment Fuel
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te t eat e t ue
Injector "A"
P20D713
Exhaust Aftertreatment Fuel
Supply Control
P20DA00
Exhaust Aftertreatment Fuel
Supply Control Circuit High
P20D900
Exhaust Aftertreatment Fuel
Supply Control Circuit Low
P24F813
Exhaust Aftertreatment Fuel
Air Purge Valve Control
Check the AHI Module
Electrical connection and
wiring harness
Circuit
P24FA00
Exhaust Aftertreatment Fuel
Air Purge Valve Control
Circuit Low
P24FB00
Exhaust Aftertreatment Fuel
Air Purge Valve Control
Circuit High
P20DD00
Exhaust Aftertreatment Fuel
Pressure Sensor
P20E000
Exhaust Aftertreatment Fuel
Pressure Sensor Circuit High
Check AHI Pressure
Sensor Electrical
Connector and wiring
harness
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.
; Live UI
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AHI Nozzle
Component Overview
The AHI Nozzle (also called the 7th injector) is mounted on the diffuser
located directly on the outlet of the turbocharger turbine housing. The 7th
injector atomizes fuel going into the exhaust stream. Some versions of
the nozzle also regulate the amount of fuel being injected.
The primary failure mode of the AHI Nozzle is a clogged/plugged nozzle
tip. A complaint of failed regens or constant request of regen is a
common associated complaint. If the AHI Nozzle is clogged, it will either
not inject a sufficient amount of fuel into the exhaust, or it will not properly
atomize the fuel to distribute it evenly throughout the DOC. Both of these
conditions will not produce the required temperatures for a successful
regen.
There have been a few different Types of AHI Nozzle over the past
several years. Use the table below as a guide along with Impact parts
information to ensure the proper Nozzle is installed on the vehicle.
OBD Level Description
Part
Number
2013-2016
Low Flow
Nozzle
21407621
2017-2018
High Flow
Type 1
21407772
Picture
; Live UI
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OBD Level Description
2019 and
newer
High Flow
Type 2
Part
Number
Picture
23937771
Diagnosis and Repair
• Check the Adaptive Factor for the AHI system by using operation 254508-03-02 Exhaust Aftertreatment Diagnostics, Options C in Premium
Tech Tool.
- If the Adaptive Factor is higher than 1.2:
○ Replace the AHI Nozzle
○ Reset the Adaptive Factor using the option in PTT
○ Run a Service Regeneration. Ensure that the temperature
graph looks similar to the one in the image below.
- If the Adaptive Factor is lower that 1.2:
○ The AHI nozzle is NOT the likely cause of the failed
regeneration. Symptom Based Diagnostics in PTT should be
followed from this point.
; Live UI
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Rules for Replacement
The AHI Nozzle is a maintenance item that requires replacement at 150K
Miles/4500 hrs in accordance with SAG documentation. The AHI Nozzle will
be denied on a warranty claim unless proof of proper maintenance is
provided.
Standard Diagnostic Time for the AHI Nozzle is 1.4 hours
Fuel and Air Lines
Component Overview
These lines run from the AHI Module to the Nozzle and are two-piece
metal lines. With start of production 2017 these lines have a limited
serviceability (3 times only) that are marked with plastic clips.
The primary failure mode of these lines is leaking (fuel/air) at the points of
connection. Because of the atomized fuel and air this leaking may not be easily
noticeable.
UI
; Live
2017 VGT Engine
2017 TC Engine
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Diagnosis and Repair
These lines are only to be tightened 3 times before
they require replacement. This applies to both connection points of the
lines (AHI Module and AHI Nozzle). When new, two plastic C-clips are
installed on each of the lines. Each time a line is removed and retightened, one of the plastic clips is to be removed. When there are no clips
left on the line it should be replaced with a new one.
Lines are to be torqued in accordance with the table below.
NOTE: It is extremely important to follow proper torque to reduce
premature line failure.
Torque Specifications
US17 and newer
Air/Fuel Line Fittings
25 ± 6 Nm (221 ± 53 in-lb)
Connection Joint
15 ± 2 Nm (135 ± 18 in-lb)
US13 through US16
Air/Fuel Line Fittings
Connection Joint
22 ± 2 Nm (195 ± 18 in-lb)
22 ± 2 Nm (195 ± 18 in-lb)
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Tags
mack
p20e000
; Live UI
p20cf7a
p24f700
p20d713
p20d000
p20dc00
p20de00
p24fb00
p24f600
p269a00
p269900
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p269713
p20dd00
p24f813
p24fa00
ahi nozzle
p20da00
volvo
unlocking uptime
Related links and attachments
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p20d900
ahi module
7th injector
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