Kenworth T680 SPN 1046 FMI 4 Engine EGR Mixer Temp Sensor Low Voltage

Question

My 2016 Kenworth with a Paccar MX-13 is throwing a derate warning and the 1046 code keeps popping up on my dash. The truck feels like it is losing pulling power on hills and the fan seems to stay engaged longer than usual. I need to get this fixed before my next haul because I can't risk a full 5-mph derate on the interstate.

hd_trucker_77 · Accepted Answer

The issue was a combination of a failed sensor and a frayed wire in the main engine harness about 4 inches back from the connector. I replaced the sensor with Paccar part #1904122 (approx $115) and spliced in a new pigtail kit. After repairing the wiring and heat-shrinking the connections, the SPN 1046 cleared immediately and the truck regained full boost pressure on the test drive.

dieselmike88 · Answer

Check the wiring harness where it runs over the top of the valve cover. Paccar engines are notorious for vibration rubbing through the loom and grounding out the signal wire to the block, which would trigger that FMI 4 low voltage code.

Jordan Lee · Answer

It's likely the sensor itself has internally failed. These mixer sensors take a beating from the heat cycles of the EGR gas and the moist air coming off the CAC. Verify you have 5V reference and a solid ground at the connector before buying parts.

backyard_bart · Answer

You should pull the sensor out and check for heavy soot buildup. If the sensor tip is completely bridged with carbon, it can't read correctly. While you have it out, measure the resistance across the pins to see if it's within the 200-300 ohm range at room temp.

Kenworth T680 SPN 1046 FMI 4 Engine EGR Mixer Temp Sensor Low Voltage

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