EGT Sensors (Exhaust Gas Temperature)
Location, connector pinout, test procedure, and related fault codes for DPF inlet, DPF outlet, DOC outlet, and SCR inlet/outlet temperature sensors on Class 8 diesel trucks.
Last updated: 2026-09-20
Overview
EGT (Exhaust Gas Temperature) sensors measure exhaust temperature at multiple points in the aftertreatment system. The ECM uses these readings to control active regeneration, monitor DPF soot loading, verify SCR catalyst efficiency, and protect aftertreatment components from overtemperature. A failed EGT sensor can cause false regeneration inhibits, derate, or DEF inducement.
Sensor Locations by Platform
Cummins X15
Multiple sensors on aftertreatment housing: DOC inlet (before DOC), DPF inlet (between DOC and DPF), DPF outlet (after DPF), SCR inlet (before SCR), SCR outlet (after SCR). All threaded into exhaust bung fittings on the aftertreatment canister.
X15 EGT sensors are accessible from the passenger side of the aftertreatment housing.
PACCAR MX-13
Aftertreatment housing — passenger side. DOC inlet, DPF inlet/outlet, SCR inlet/outlet sensors all threaded into bung fittings on the aftertreatment canister.
MX-13 EGT sensor connectors are exposed to road splash — inspect for corrosion.
Detroit DD15
Aftertreatment housing — passenger side. Multiple EGT sensors threaded into the aftertreatment canister at DOC inlet, DPF inlet, DPF outlet, and SCR positions.
DD15 EGT sensors require DDDL for live data monitoring during active regen.
Volvo/Mack MP8
Aftertreatment housing — passenger side. EGT sensors at DOC inlet, DPF inlet/outlet, and SCR inlet/outlet positions on the aftertreatment canister.
MP8 EGT sensor replacement requires PTT or JPRO for sensor reset after replacement.
DieselVision™ identifies sensor labels and connector pin numbers — upload a close-up photo and the system maps pins automatically.
Connector Pinout
| Pin | Function | Specification |
|---|---|---|
| A | 5V Reference or Thermocouple (+) | 4.75–5.25V (thermistor) or millivolt output (thermocouple) |
| B | Ground (Signal Return) or Thermocouple (-) | <0.1V to chassis ground |
Test Procedure
Read all EGT sensor temperatures in live data at idle (cold start)
Expected: All EGT sensors should read near ambient temperature when cold. Sensors reading -40°C or max value = circuit fault
Tool: OEM diagnostic software
After warm-up, compare EGT sensor readings across the aftertreatment system
Expected: DOC inlet: 200–400°C at idle. DPF inlet: slightly higher than DOC inlet. SCR inlet: 200–350°C. Downstream sensors should be lower than upstream
Tool: OEM diagnostic software
Measure sensor resistance across pins A and B (sensor disconnected, key off)
Expected: Thermistor type: resistance varies with temperature. Thermocouple type: very low resistance (<5 ohms). Infinite resistance = open circuit
Tool: Multimeter (ohms)
Check ground circuit resistance from pin B to chassis ground
Expected: <0.5 ohms
Tool: Multimeter
Inspect sensor bung and sensor tip for carbon buildup or physical damage
Expected: Sensor tip should be clean and undamaged. Carbon buildup can cause slow response or stuck readings
Tool: Visual inspection
During active regen, monitor EGT sensor response — all sensors should rise together
Expected: DOC inlet should reach 550–650°C during active regen. Sensors that do not rise = failed sensor or circuit fault
Tool: OEM diagnostic software
Common Failure Modes
- •Open circuit — sensor reads -40°C or minimum value
- •Short to ground — sensor reads maximum temperature
- •Internal thermocouple failure — stuck or erratic reading
- •Carbon buildup on sensor tip causing slow response
- •Sensor bung corrosion causing loose sensor
- •Connector corrosion from heat cycling
- •Sensor reading high due to active regen inhibit fault
Frequently Asked Questions
How many EGT sensors does a Class 8 diesel have?
Most Class 8 diesel aftertreatment systems have 4–5 EGT sensors: DOC inlet, DPF inlet, DPF outlet, SCR inlet, and SCR outlet. The exact number varies by OEM and model year.
What temperature should EGT sensors read at idle?
At warm idle, DOC inlet EGT is typically 200–400°C, DPF inlet is slightly higher, and SCR inlet is 200–350°C. Cold sensors reading near ambient is normal before warm-up.
What does an EGT sensor reading of -40°C mean?
A reading of -40°C (minimum value) indicates an open circuit in the sensor or signal wire. Check sensor resistance and wiring continuity.
What fault codes are caused by a failed EGT sensor?
Common fault codes include SPN 3031 (DOC inlet temp), SPN 3216 (DPF inlet temp), SPN 3226 (DPF outlet temp), and SPN 3246 (SCR outlet temp) with FMI 3 or FMI 4.
Snap a photo of your scan tool screen and let Diesel Vision interpret the fault instantly — no manual code lookup required.
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