OBD2 Sensors >> Paccar MX11 / MX13 I6 Engine Sensor Locations

Which engine do you have? The photographs and the locations below are a 2012 PACCAR MX-13, which is an EPA10 build. Later MX-13s move a small number of sensors, and the MX-11 is closely related but has not been checked position by position, so confirm against your own engine before you start cutting zip ties.

1. Common Rail Fuel injectors (under valve cover center of cylinder head)
2. Unit Pumps (rear of engine fitted to engine block)
3. Fuel Rail Pressure Sensor (middle of fuel rail)
4. Supply Fuel Pressure Sensor (located on driver side rear of engine)
5. Fuel Temp Sensor (located on driver side rear of engine)
6. Camshaft position sensor (CMP) (located at the back of engine on the bellhousing)
7. Crankshaft position sensor (CKP) (located at the back of engine on the bellhousing)
8. Oil pressure sensor (driver’s side of engine block behind alternator)
9. Oil Temperature Sensor (behind oil filters)
10. Turbocharger Speed Sensor (center of turbocharger housing)
11. Turbocharger Compressor Intake Pressure/Temp Sensor (inlet of compressor side of turbo)
12. VGT Actuator Position Sensor (inside VGT actuator)
13. Exhaust Gas Temp Sensor (above Air Fuel ration Sensor in exhaust)
14. Coolant temperature sensor (located at right rear of engine)
15. Exhaust Gas Pressure Sensor (attached to exhaust manifold towards front of engine)
16. Exhaust Backpressure Sensor (attached to EGR Cooler inlet towards rear of engine)
17. Charge Air Cooler Temp Sensor (attached to air inlet at intake manifold)
18. EGR Mass Flow / Temp sensor (front of engine near lifting eye)
19. EGR Temp Sensor (attached to EGR crossover pipe in front of engine)
20. EGR Valve Position Sensor (attached behind EGR Valve)
21. Air Fuel Ratio Sensor (outlet of turbine side of turbocharger)
22. Barometric Pressure Sensor (attached to side of ECM)
23. Intake Manifold Temp and Pressure Sensors (driver side of intake manifold at front of engine)
24. Crankcase Pressure Sensor (arrowed in red on the driver side photo – low at the front of the block, behind the frame rail)

4. Supply Fuel Pressure Sensor

Monitors the fuel pressure entering the low-pressure supply circuit to ensure the fuel system remains fully charged before delivering fuel to the high-pressure injection pump. The ECM uses this data to adjust lift pump performance and calculate precise injection volume compensation based on the pressure in the low-pressure fuel system. Sensor faults or restricted fuel delivery typically cause severe engine power loss under heavy acceleration, low power codes under load, rough idling, or extended engine cranking times during startup due to drops in fuel system pressure.

Where it is. The supply fuel pressure sensor, number 4 in the list and the driver’s-side photograph above, is located on the driver’s side rear of the engine block. It is threaded horizontally directly into the integrated fuel module housing block, positioned just forward of the flywheel bell housing and vertically below the primary fuel rail assembly. Look for a brass-bodied sensor with a hexagonal base and a black, plastic 3-pin electrical connector pointing toward the rear firewall.

Getting at it. Replacement is a moderately simple 30-minute driveway job, though working space is limited against the cab firewall overhang. No major mounting brackets or primary high-pressure fuel lines need to be disconnected for removal, but the secondary engine wiring harness must be unclipped for tool clearance. The job requires a 24mm deep socket or open-ended wrench, and a small drain pan to catch the small amount of diesel fuel that will spill from the gallery when the sensor is removed.

Codes: SPN 94 with FMI 3 or 4 indicates an un-synchronized, excessively high, or missing low-pressure fuel system voltage return signal.

Fitting it. This sensor relies on a Viton rubber O-ring at the base of the threads to contain pressurized diesel fuel within the module housing. Never install the sensor completely dry or use generic RTV silicone or white PTFE tape, which can shred and clog the internal fuel orifices. Instead, apply a clean smear of fresh engine oil or clean diesel fuel to the rubber O-ring to prevent it from pinching or shearing when threaded in. When installing the sensor, tighten it to 30 Nm using a calibrated torque wrench, as over-torquing can easily strip out the aluminum threads inside the expensive fuel module casting.

How it typically fails. Sitting directly on the main fuel module exposes this sensor to continuous, high-frequency engine vibration and extreme heat radiating from the block. Over time, these conditions cause internal micro-cracks in the plastic connector housing, allowing fuel to short out the internal sensing element. Additionally, if fine metal debris or heavy asphaltene contamination accumulates inside the small sensor inlet port, the pressure readings will drift out of range, prompting the ECM to initiate a power derate.

8. Engine Oil Pressure Sensor

Monitors lubricating system pressure across all engine operating ranges, and feeds real-time voltage signals directly to the engine ECU. The control module processes these inputs to drive the instrument cluster pressure gauge, calculate variable engine lubrication demands, and activate warning lamps or engine protection derate modes if system pressure falls below a minimum allowable threshold. Sensor faults typically trigger low oil pressure warning alarms, inaccurate or erratic oil-pressure gauge readings, or unexpected engine power derates.

Where it is. The engine oil pressure sensor, number 8 in the list and the driver’s-side photograph above, is located on the driver’s side of the engine block near the front. It sits directly behind the alternator assembly and just above the accessory drive alignment area. Look for a compact, brass-threaded sensor with a round plastic housing and a 3-pin locking electrical connector.

Getting at it. Replacement is a 20-to-30-minute driveway job, though workspace access is tight due to the alternator housing and its mounting brackets. Use a specialized deep-well oil pressure sensor socket to prevent breaking the sensor off in the engine block while working in a tight space, paired with a medium extension and ratchet. You do not need to drain engine oil prior to swapping this component, as it sits above the static oil pan level.

Codes: SPN 100 with FMI 3 or 4 indicates an electrical circuit high or low condition, while FMI 1 or 18 signals severe oil pressure that has dropped below a pre-programmed minimum limit.

Fitting it. Clean away road dirt and grime around the sensor before removing the old unit to prevent engine grime or debris from entering the primary oil gallery. Apply an approved thread sealant other than RTV silicone, or a light wrap of PTFE tape around the male brass threads on the replacement sensor to prevent oil weeping past the threads in the engine block. Thread the sensor into the block by hand first to ensure threads engage smoothly, then tighten firmly; avoid over-torquing to prevent stripping the soft brass threads or damaging the engine block casting.

How it typically fails. Constant engine vibration and heat cycling cause the sensor’s internal pressure diaphragm and electrical potting material to fail over time, allowing pressurized engine oil to seep into the internal sensor connector housing. Check the female terminal harness for oil intrusion or pin push-outs, as oil-soaked connectors will skew voltage readings and cause phantom low-pressure codes even after installing a new sensor.

9. Oil Temperature Sensor

Monitors the temperature of the engine oil after it passes through the oil cooler to ensure the stability of the lubricating oil film under heavy load. The ECM relies on this thermal input to adjust variable oil pump displacement parameters, calculate oil degradation, and coordinate with the engine protection module to activate warning alerts if the oil temperature reaches a maximum allowable threshold. Sensor failures or inaccurate signals typically cause the dash gauge to read erratic, prompt constant false high-temperature visual alerts, cycle the main engine cooling fan clutch to full lockup, or trigger a protective power-derate mode.

Where it is. The oil temperature sensor, number 9 in the list and the opposite-side photograph above, is threaded horizontally into the rear flank of the integrated oil module assembly housing, positioned immediately behind the main oil filters and vertically above the oil pan rail junction. Look for a single-bolt style or threaded brass probe fitted with a black, two-pin weather-sealed electrical connector housing that plugs directly into the lower leg of the primary engine injector and sensor wiring harness loom.

Getting at it. Replacement is a simple 20-minute driveway job that can be completed during a standard routine oil change while the system is drained. If the engine is full of oil quickly swap the new sensor in or place a wide drain pan beneath the filter module to capture the oil that will rapidly spill out of the internal sensor galley channel when the sensor is removed. This job requires a 19mm deep socket or open-ended line wrench, and a lint-free shop rag to clean the surrounding sealing face.

Codes: SPN 175 with FMI 3 or 4 indicates a short-circuit to ground or an open-circuit failure within the engine oil temperature sensing voltage return loop.

Fitting it. This sensor relies on a dedicated crush washer or a specialized high-temperature rubber barrel O-ring situated at the base of the brass hex head to seal engine oil within the pressurized filter block. Never use standard white PTFE thread tape or liquid RTV silicone compounds on the body, as loose pieces can break off into the clean oil stream and lodge inside the engine bearings. Instead, lubricate the sealing ring with a clean film of fresh engine oil to ensure a distortion-free seal. Torque the sensor to 25 Nm using a calibrated torque wrench, as over-tightening can easily fracture the thin metal sensor body or strip the aluminum threads out of the oil module housing.

How it typically fails. Being mounted directly to the engine’s main oil filter module subjects this sensor to intense heat soaking and continuous low-frequency mechanical vibration. Over hundreds of thousands of miles, the constant thermal loading hardens the internal plastic insulation, causing it to crack and permit pressurized engine oil to wick directly past the pins into the external harness connector plug to cause a short circuit.

14. Engine Coolant Temperature Sensor

Monitors the precise temperature of the engine coolant. The ECM relies on this continuous voltage feedback to regulate fuel injection timing adjustments, calculate diesel exhaust fluid (DEF) injection rates, command the engine cooling fan clutch duty cycle, and protect the cylinder head from overheating. Sensor failures or out-of-range signals typically cause extended engine cranking times on cold starts, the cooling fan locking up at 100% engagement continuously, an abnormal reading on the temperature gauge, or a power derate.

Where it is. The engine coolant temperature sensor, number 14 in the list and the opposite-side photograph above, is located on the rear passenger side of the engine block assembly. It is threaded horizontally directly into the integrated coolant distribution manifold housing, situated forward of the flywheel bell housing flange and positioned vertically just beneath the cylinder head deck mating line. Look for a brass-bodied sensor with a hexagonal base and a black, two-pin weather-sealed electrical connector housing branching directly off the rear channel of the main engine wiring loom.

Getting at it. Replacement is a 30-45-minute driveway job that requires draining the radiator block before attempting to unthread the component to prevent a massive coolant spill. No heavy mounting brackets or fuel delivery modules need to be disassembled, although the upper exhaust heat shielding clips must be undone to establish a clear line of sight near the firewall. The job requires a 19mm deep socket or open-ended line wrench, a 3/8-inch drive ratchet with a 3-inch extension bar, and a clean drain pan to capture the coolant.

Codes: SPN 110 with FMI 3 or 4 indicates an out-of-range high voltage, open circuit, or an excessively low voltage short-to-ground fault within the primary cooling system’s signal circuit.

Fitting it. This sensor relies on brass threads interfacing with the cast-iron housing, and is sealed at its base with a specialized, single-use copper crush washer. Never use standard white Teflon thread tape or generic RTV silicone compounds on the body, as loose fragments can shear off into the cooling paths and block narrow passages inside the EGR cooler. Instead, install the sensor with a thin, uniform bead of high-temperature liquid thread sealant applied strictly to the male threads. Tighten the sensor to 22 Nm using a calibrated torque wrench, as over-tightening risks cracking the internal ceramic thermistor element or stripping the threads.

How it typically fails. Being tucked into the right rear corner of the block subjects this sensor to intense heat-soaking and concentrated exhaust heat every time the truck is shut down. Over extended periods, heat cycling hardens the internal potting material, allowing pressurized coolant to wick directly past the pins into the external harness connector plug to cause a short circuit.

15. Exhaust Gas Pressure Sensor

Monitors the exhaust backpressure generated by the engine upstream of the turbocharger turbine wheel to manage the variable geometry turbocharger (VGT) vane positioning. The ECM uses this pressure data to calculate precise exhaust gas recirculation (EGR) flow differentials and manage engine braking limits safely. Sensor faults or implausible readings typically cause sluggish throttle response, sudden drops in fuel economy, severe turbocharger surging, erratic engine brake operation, and automatic prevention of active DPF regeneration cycles.

Where it is. The exhaust gas pressure sensor, number 15 in the list and the opposite-side photograph above, is located on the passenger (turbo) side of the engine block. It is bolted vertically onto a dedicated support bracket positioned near the top-center quadrant of the block, situated horizontally above the main exhaust manifold assembly. Look for a compact plastic and metal body connected directly to a rigid, curved stainless steel sampling tube that runs straight down into the front section of the cast-iron exhaust manifold.

Getting at it. Replacement is a 30-minute driveway job, though you must wait for the entire exhaust system to cool completely to avoid severe burns and other personal injuries. No major brackets or coolant lines need to be removed, but the rigid metal pressure tube must be unbolted to inspect for carbon blockages. Replacing the sensor requires a 22mm open-ended wrench for the tube nut, a 10mm socket for the mounting bracket fasteners, a 3/8-inch drive ratchet, and a small pick or wire brush to clear soot out of the metal feed line port.

Codes: SPN 1209 with FMI 3 or 4 indicates an out-of-range high or low pre-turbine exhaust pressure signal to the controller.

Fitting it. This sensor relies on a specialized compression fitting on the metal line and an internal rubber seal inside its electrical connector plug to isolate the sensor element. Never use standard white Teflon tape or soft RTV silicone on the hot metal fittings, as the intense exhaust heat will incinerate the material and contaminate the sensing element. Instead, assemble the metal compression fittings completely dry or with a drop of specialized high-temperature anti-seize applied strictly to the male threads. When installing the sensor to its bracket, snug the fasteners down firmly with small hand tools to avoid cracking the molded composite mounting eyelets.

How it typically fails. Sitting directly above the exhaust manifold subjects this sensor to intense heat and extreme, high-frequency exhaust pulses. Over extended periods, repeated heat cycling bakes the internal silicone gel protection solid, destroying the delicate piezoresistive sensing bridge inside the sensor housing. Additionally, the narrow metal feed tube running from the exhaust manifold frequently plugs solid with heavy carbon soot deposits, which traps pressure inside the line and causes the sensor to get stuck on erratic or fixed pressure values.

23. Intake Manifold Pressure Sensor

Monitors the precise absolute pressure of the compressed air filling the intake runner plenum after it passes through the charge air cooler. The ECM continuously cross-references this boost data with engine speed and temperature inputs to calculate and manage precise fuel injection volumes, and regulate emission levels. Sensor failures or out-of-range pressure values typically cause an immediate lack of throttle response, excessive black smoke from the exhaust under load, hard starting, poor fuel efficiency, and a severe loss of total engine power due to the ECM reducing fuel delivery.

Where it is. The intake manifold pressure sensor, number 23 in the list and the driver’s-side photograph above, is located on the driver’s side of the intake manifold assembly near the front of the engine. It is mounted vertically into the upper cast aluminum intake runner tube casting, positioned horizontally forward of the electronic fuel module and vertically above the main alternator assembly mounting bracket. Look for a small, rectangular composite plastic component secured by a single hold-down bolt, featuring an integrated 4-pin wiring connector plug facing toward the side frame rail.

Getting at it. Replacement is a simple 20-minute driveway job, and no heavy structural brackets, fuel supply lines, or large air intake tubes need to be disassembled, although clearing the front section of the engine wiring loom from its retention clips makes tool access much easier. This job requires only a T30 Torx socket or an 8mm nut driver, a 1/4-inch drive ratchet extension handle, and a clean shop rag to wipe away oily residues from the manifold mounting surface.

Codes: SPN 102 with FMI 3 or 4 indicates an out-of-range high voltage open circuit or an excessively low voltage short-to-ground fault within the intake boost pressure signal loop.

Fitting it. This sensor relies on a specialized, high-temperature square-cut green or black rubber seal nested around its lower probe neck to retain high-pressure turbocharger boost air within the manifold runner. Never apply liquid RTV gasket maker, copper spray, or thread sealing tape to the plastic probe body, as these materials will clog the internal silicon pressure-sensing chip and ruin the sensor’s performance. Instead, coat the rubber seal in a very thin layer of clean engine oil to help it slide smoothly into the aluminum bore without pinching. Tighten the single mounting bolt to 9 Nm using hand tools, as over-tightening will easily strip the soft aluminum threads in the intake casting or crack the plastic mounting eyelet.

How it typically fails. Being situated directly on the main fresh-air intake tract exposes this sensor to continuous oil mist carrying over from the crankcase ventilation system along with abrasive carbon soot blown back from the EGR valve crossover pipe. Over time, this thick, sticky mixture forms a sludge layer that completely plugs the tiny sampling orifice on the tip of the sensor probe, which prevents the sensing element from detecting pressure changes. Additionally, the constant thermal expansion and contraction cycles of the intake runner cause the plastic housing to develop micro-fractures, allowing environmental moisture to enter the internal electronics and cause intermittent signal drops.

24. Crankcase Pressure Sensor

Monitors the internal gas pressure building within the engine crankcase to track the health of the pistons, rings, and cylinders. The ECM continuously reads this internal pressure value to detect excessive blow-by gases, verify the operation of the closed crankcase ventilation (CCV) system, and protect internal seals from blowing out under high load. Sensor faults or escalating crankcase pressure readings will prompt immediate dashboard warning lamps, cause severe oil leaks around structural oil seals, hurt fuel economy, or trigger an uncommanded engine shutdown to prevent engine failure.

Where it is. The crankcase pressure sensor is arrowed in red on the driver’s-side photograph above, because it is very hard to pick out otherwise. It sits on the lower driver’s side front quadrant of the engine block. It is tucked lower down behind the main vehicle chassis frame rail channel, positioned vertically directly below the fuel filter module assembly and sitting just behind the primary closed crankcase ventilation (CCV) module separator canister. Look for a small plastic sensor with an integrated 3-pin electrical harness plug, linked directly to a short, rigid plastic sampling pipe that branches straight out of the lower CCV main pressure line.

Getting at it. Replacement is a 45-minute, strictly shop floor maintenance job that is best performed by accessing the block from underneath the vehicle chassis. The sensor is deeply buried, meaning you must unbolt and set aside the primary ECM wiring harness brackets and clear the lower fuel supply line loops out of the way to squeeze tools into the gap. The job requires a T27 Torx driver socket to remove the small retention fastener, a 1/4-inch drive ratchet extension, a clean pick to unclip the harness safety tab, and a flashlight to illuminate the dark cavity behind the frame rail.

Codes: SPN 101 with FMI 2, 3, or 4 indicates implausible signal values, shorted high-voltage open circuits, or a complete loss of signal ground within the engine blow-by measurement loop.

Fitting it. This sensor features a dedicated internal rubber barrel O-ring surrounding its composite probe neck to seal back-pressure within the plastic CCV sampling tube interface. Never apply standard white Teflon thread tape or liquid silicone RTV compounds to the plastic body, as debris can block the delicate internal transducer plate and permanently destroy the component’s performance. Instead, coat the rubber barrel seal with a light drop of clean engine oil before installation to ensure it presses smoothly into the bore without binding. Snug the single Torx hold-down screw firmly using hand tools only, as over-torquing will easily snap the fragile composite mounting ear.

How it typically fails. Positioned lower down on the side of the engine block exposes this sensor to constant high-amplitude engine vibrations and harsh road grit splashing up from the front wheel wells. Over extended periods, this relentless vibration chafes the engine wiring harness pins against the frame rail edges, causing intermittent open circuits or false high-voltage returns. Additionally, heavy oil sludge mist and soot traveling through the crankcase breather system will pool directly inside the narrow sensor-sampling orifice, preventing the sensor from detecting crankcase pressure variations, thus locking the signal on a fixed value.

Engine Found in These Trucks (starting 2010-current):

• Kenworth
• Peterbilt
• Leyland Truck
• DAF