Diesel Truck Component Locations: Where to Find Everything by Model

Why Knowing Component Locations Matters

Every minute a tech spends searching for a component is a minute not spent diagnosing the problem. For new technicians — or shops working on an unfamiliar engine — knowing exactly where to find the ECM, ACM, NOx sensors, DEF doser, and DPF can save hours per job.

This is especially critical during remote diagnostic sessions, where our team needs the on-site tech to physically check specific components. "Go check the outlet NOx sensor" only works if the tech knows where it is.

Cummins ISX15 / X15 / ISB 6.7

ECM (Engine Control Module)

• ISX15 / X15: Driver side of the engine block, below the intake manifold, near the fuel filter housing. Look for a large aluminum module with two or three harness connectors.
• ISB 6.7: Passenger side of the engine, near the top. Mounted to the engine block with a bracket.
• ECM Platform: CM2350 (2013-2019) or CM2450 (2020+)

ACM (Aftertreatment Control Module)

• Mounted on the aftertreatment frame rail bracket, passenger side, near the DPF canister
• Gray or black plastic housing with weatherproof connectors
• Follow the aftertreatment harness from the DPF area to find it

Turbocharger (VGT)

• ISX15: Top center of engine, between the exhaust manifolds
• Variable Geometry Turbo with electronic actuator on top (black round motor)
• The actuator is the common failure point — look for the electrical connector on top of the turbo housing

EGR Valve & Cooler

• ISX15: Front of engine, passenger side
• EGR cooler is the large tube-like component running between the exhaust manifold and the intake
• EGR valve sits on top of or beside the cooler — look for the electrical connector

DPF / DOC / SCR System

• Frame rail mounted, passenger side
• Order (front to back): DOC (smaller canister) → DPF (larger canister) → Decomposition Tube → SCR
• 5th injector (HC doser): Mounted on the exhaust pipe at the DOC inlet — this is the fuel injector that creates heat for active regens
• The decomposition tube between DPF and SCR is where DEF is injected and mixes with exhaust

NOx Sensors

• Inlet NOx (SPN 4360): Mounted on the exhaust pipe between the turbo outlet and DOC inlet
• Outlet NOx (SPN 4094): After the SCR catalyst, near the tailpipe
• Both are 5-wire sensors with large connectors — look for the wiring harness running along the frame rail to each sensor

DEF Components

• DEF tank: Usually driver side frame rail, behind or below the fuel tank. Blue cap.
• DEF dosing unit (injector): Mounted on the decomposition tube between DPF and SCR
• DEF pump/supply module: Near the DEF tank, often inside or attached to the tank
• DEF level sensor (SPN 3226): Inside the DEF tank — requires tank access to replace

On Cummins, the 5th injector (HC doser) coking is the #1 cause of failed active regens. It's on the DOC inlet pipe — look for a small fuel injector with a supply line running to the fuel system.

Detroit DD13 / DD15 / DD16

MCM (Motor Control Module) — Detroit's ECM

• DD15: Driver side of the engine block, near the oil filter housing
• Large silver/gray aluminum box with two large harness connectors
• It's the primary engine computer — equivalent to the ECM on other brands

CPC (Common Powertrain Controller)

• Under the dash, inside the cab, behind the instrument panel
• This is unique to Detroit — no other brand has a second engine controller inside the cab
• The CPC handles: transmission communication, body control, ABS interface, parameter settings
• If you're diagnosing transmission shifting issues on a Detroit, check the CPC inside the cab, not just the MCM on the engine

ACM (Aftertreatment Control Module)

• Frame rail, passenger side, mounted near the one-box aftertreatment
• Controls DEF dosing, DPF regen, NOx monitoring

One-Box Aftertreatment (DPF/DOC/SCR)

• Detroit uses a "one-box" design — DOC, DPF, and SCR are all inside one large canister
• Passenger side frame rail, usually behind the cab
• The one-box is HEAVY (200+ lbs) — requires a support jack or hoist for removal
• Internally: DOC section (front) → DPF section (middle) → SCR section (rear)

Delta-P (Differential Pressure) Sensor

• Mounted on top of or near the one-box
• Two rubber tubes connect to ports before and after the DPF section
• These tubes are the #1 maintenance item on Detroit — they clog with soot constantly
• A clogged tube causes false high soot readings → unnecessary regen attempts → SPN 4334
• Before replacing the sensor ($400), clean the tubes first ($15 fix)

NOx Sensors

• Inlet: Mounted on the exhaust pipe before the one-box entrance
• Outlet: After the SCR section at the one-box exit, near the tailpipe connection

Turbocharger

• DD15: Top center-rear of the engine
• Asymmetric twin-scroll turbo with electronic wastegate actuator
• Turbo actuator failures are common — look for the electronic connector on the actuator arm

EGR System

• DD15: Front of engine, driver side
• EGR cooler is integrated into the cylinder head area
• EGR valve is accessible from the front of the engine

Detroit CPC is inside the cab. If you have transmission faults or parameter issues on a DD13/DD15, check under the dash — not just under the hood.

PACCAR MX-13 / MX-11

ECM

• MX-13: Driver side of the engine block, behind the coolant filter housing
• Look for the silver module with harness connectors on the lower-left area of the engine

ACM

• Frame rail, passenger side, near the aftertreatment canisters
• Similar location to other brands

Turbocharger (VGT)

• Top of engine, center-rear position
• Variable geometry with electronic actuator
• VGT actuator sticking is a known issue — the actuator motor is on top of the turbo

DPF / DOC / SCR (Two-Canister System)

• PACCAR uses two separate canisters on the passenger side frame rail (unlike Detroit's one-box)
• First canister (front): DOC + DPF combined
• Second canister (rear): SCR catalyst + ammonia slip catalyst
• Decomposition tube connects the two with the DEF doser mounted on it

HC Doser (Hydrocarbon Doser) — CRITICAL COMPONENT

• Mounted on the exhaust pipe before the first canister (DOC inlet)
• This is the #1 problem component on MX-13
• It injects fuel into the exhaust to raise temps for DPF regen
• Coking (carbon buildup) is extremely common — blocks the injector nozzle
• When coked, the truck can't achieve regen temperatures → soot builds up → derate
• Location tip: follow the small fuel supply line from the engine to the exhaust pipe — it connects to the HC doser

NOx Sensors

• Inlet: On the exhaust pipe between engine and first canister
• Outlet: After the second canister (SCR), near the tailpipe

DEF Components

• DEF tank: Driver side frame rail, blue cap
• DEF doser/injector: On the decomposition tube between canister 1 and canister 2
• DEF supply module: Near or on the DEF tank

On PACCAR MX-13, always inspect the HC doser at every DPF service. If it's coked, clean or replace it before the DPF. A new doser is $200-400 — much cheaper than a new DPF.

International MaxxForce / A26

ECM

• MaxxForce: Driver side of the engine block
• A26: Driver side, similar position to Cummins

EGR System (MaxxForce — CRITICAL)

• EGR cooler: Front of engine, very large component — can't miss it
• EGR valve: On top of the EGR cooler
• MaxxForce used an EGR-only emissions strategy (no SCR/DEF system)
• This puts extreme thermal stress on the EGR cooler → internal cracking is very common
• Signs of EGR cooler failure: coolant loss with no visible leak, white exhaust smoke, coolant staining around the EGR cooler
• If you see wetness or coolant residue around the EGR cooler area, it's likely cracked internally and mixing coolant with exhaust

DPF (MaxxForce)

• Frame rail, passenger side
• MaxxForce has NO SCR — no DEF tank, no DEF doser, no SCR catalyst
• All particulate reduction relies solely on the DPF
• This means higher soot loading rates and more frequent regen cycles than modern engines

A26 Aftertreatment (Modern System)

• The A26 does have full SCR/DEF like Cummins and PACCAR
• DOC → DPF → SCR on the passenger frame rail
• DEF tank on driver side
• Layout is similar to Cummins

Quick Reference Table

For engine-specific diagnostic support, visit our brand pages: Cummins | Detroit | PACCAR | International

To understand how all these components communicate, read our guide on how the ECM controls everything.