PACCAR MX-13 Load Disconnect Switch Mismatch SPN 520202 FMI 14

Question

I have a 2019 Peterbilt 579 that keeps throwing a yellow check engine light and an electrical system fault on the dash. Using Davie 4, I am seeing a persistent SPN 520202 FMI 14 code related to the battery disconnect switch state mismatch. The truck starts fine, but some of the sleeper accessories lose power intermittently while driving.

Brian O'Connor · Accepted Answer

The issue was the Load Disconnect Solenoid located behind the battery box. The internal contacts were burnt, causing a high resistance that the CECU flagged as a state mismatch. I replaced the solenoid (Part # P27-6100-111) and cleaned the terminal rings for the 4AWG cables. I also found a corroded pin in the 2-pin connector at the solenoid. After clearing the codes with Davie 4 and cycling the key, the fault stayed inactive and accessory power was restored. The part was about $140 and took 2 hours to install.

Sarah Thompson · Answer

Check the feedback circuit going back to the CECU. This code usually triggers when the V-CAN signals don't match the hardwired state of the switch sensing line.

backyard_bart · Answer

Inspect the wiring harness near the battery box hinge. Those wires tend to rub and chafe right where they exit the box, which can cause a short to ground and confuse the controller about the switch position.

hd_trucker_77 · Answer

Make sure your batteries are actually holding a load. Sometimes if the voltage drops too low during the initial self-test of the CECU, it interprets the voltage drop as a switch mismatch error.

PACCAR MX-13 Load Disconnect Switch Mismatch SPN 520202 FMI 14

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