EGR Sensors (Mass Flow & Temperature)
Location, connector pinout, and test procedures for EGR mass flow and EGR temperature sensors on Class 8 diesel trucks.
Last updated: 2026-09-20
Overview
EGR sensors monitor the exhaust gas recirculation system. The EGR mass flow sensor (differential pressure type) measures EGR flow rate, while the EGR temperature sensor monitors the temperature of recirculated exhaust gas. The ECM uses these readings to control EGR valve position and maintain target EGR flow. Failed EGR sensors cause derate, excessive NOx emissions, and active regen inhibits.
Sensor Locations by Platform
Cummins X15
EGR mass flow sensor: mounted on EGR cooler outlet or EGR mixer, driver side. EGR temperature sensor: threaded into EGR cooler outlet pipe.
X15 EGR mass flow sensor is a differential pressure type — check both pressure ports for plugging.
PACCAR MX-13
EGR mass flow sensor: driver side, on EGR cooler outlet. EGR temperature sensor: threaded into EGR pipe near cooler outlet.
MX-13 EGR sensors are accessible from the driver side with air cleaner removed.
Detroit DD15
EGR mass flow sensor: driver side, mounted on EGR mixer or cooler outlet. EGR temperature sensor: threaded into EGR cooler outlet.
DD15 EGR cooler is a common failure point — inspect cooler before replacing sensor.
Volvo/Mack MP8
EGR mass flow sensor: driver side, on EGR cooler outlet pipe. EGR temperature sensor: threaded into EGR cooler outlet.
MP8 EGR system uses a variable geometry EGR valve — verify valve operation before condemning sensor.
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 | 4.75–5.25V |
| B | Ground (Signal Return) | <0.1V to chassis ground |
| C | Signal Output (Mass Flow or Temp) | 0.5–4.5V range |
Test Procedure
Read EGR mass flow and EGR temperature in live data at idle
Expected: EGR mass flow: 5–20 kg/h at warm idle. EGR temp: 150–300°C at warm idle. Zero flow with EGR commanded open = sensor or valve fault
Tool: OEM diagnostic software
Measure 5V reference voltage at EGR sensor harness connector
Expected: 4.75–5.25V between reference pin and ground pin
Tool: Multimeter
Check ground circuit resistance from ground pin to chassis ground
Expected: <0.5 ohms
Tool: Multimeter
Check signal wire for short to ground (sensor disconnected, key off)
Expected: >1 MΩ between signal pin and chassis ground
Tool: Multimeter
Inspect EGR cooler and EGR valve for soot plugging — plugged EGR cooler causes low flow reading
Expected: EGR passages should be clear. Heavy soot = EGR cooler cleaning or replacement needed
Tool: Visual inspection
Command EGR valve open and closed in actuator test — monitor mass flow response
Expected: Mass flow should increase when EGR valve opens and decrease when it closes
Tool: OEM diagnostic software (actuator test)
Common Failure Modes
- •EGR mass flow sensor internal failure — stuck reading
- •EGR cooler plugging causing low mass flow reading
- •EGR temperature sensor open circuit — reads -40°C
- •Connector corrosion from heat cycling
- •Signal wire short to ground
- •EGR valve stuck closed — zero flow despite sensor working correctly
Frequently Asked Questions
Where is the EGR mass flow sensor located?
The EGR mass flow sensor is mounted on the EGR cooler outlet or EGR mixer on the driver side of the engine on most Class 8 platforms.
What causes low EGR mass flow?
Common causes include a plugged EGR cooler, stuck EGR valve, failed EGR mass flow sensor, or plugged sensor pressure ports.
What fault codes are caused by a failed EGR sensor?
Common fault codes include SPN 412 FMI 2 (EGR mass flow data erratic), SPN 2659 FMI 4 (EGR temperature below normal), and SPN 1636 FMI 2 (intake manifold pressure erratic).
How do I test the EGR mass flow sensor?
Command the EGR valve open in an actuator test and monitor mass flow in live data. Flow should increase when the valve opens. If flow stays at zero with the valve open, check the sensor, cooler, and valve.
Snap a photo of your scan tool screen and let Diesel Vision interpret the fault instantly — no manual code lookup required.
Try It