2018 Freightliner Cascadia SPN 1487 FMI 2 Intermittent Dash Lights

Question

My dash lights and switch backlighting have started flickering lately while driving at night. Sometimes the intensity jumps to full bright or goes completely dark for a few seconds. This is throwing SPN 1487 FMI 2 on my diagnostic tool and it is driving me crazy during mountain passes.

Rachel Nguyen · Accepted Answer

I found the issue was a Chafed wire in the harness between the ICU (Instrument Cluster Unit) and the dash dimmer switch. Specifically, the wire identified as 467D was rubbing against a metal bracket behind the speedometer. I spliced in a new section of 18ga wire, heat-shrunk the connection, and rerouted the harness with more slack. No more flickering and the SPN 1487 code stayed inactive after a 4-hour night run. Total cost was just the price of wire and terminals.

turbo_tony · Answer

FMI 2 indicates erratic data, which often points to a grounding issue or a failing bulkhead module. Check your ground studs on the firewall; if they are corroded, the BHM wont be able to regulate the PWM signal for the dimming circuit correctly.

Jake Morrison · Answer

Check the wiring harness behind the dash near the steering column. These Cascadias are known for the steering tilt mechanism rubbing against the main harness, which can cause erratic data signals on the CAN line that controls the lighting loop.

Sarah Thompson · Answer

Since you swapped the switch and it didnt fix it, check the pins at the Bulkhead Module (BHM) Connector 3. Look for any signs of water intrusion or green crusties in the pins that handle the backlighting output.

2018 Freightliner Cascadia SPN 1487 FMI 2 Intermittent Dash Lights

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