@justwingingitgarage: Brand new cooling fan assembly and it STILL won't run?! Dissecting a 2022 Chevy Blazer with a check engine light and codes P0494 (Fan Underspeed), U0632 (Lost Comms with Cooling Fan), and U1345 (LIN Bus 1). Another shop had already replaced the entire fan assembly, but the problem remained. Commanding the fan on with the scan tool showed the blades barely twitch before cutting out. A standard test light lit up fine on power and ground, and the LIN bus communication line was clean. But when we hooked up the Micsig lab scope with an amp clamp, we saw voltage at the fan connector plummet to 6–7 volts the moment current tried to ramp up! Probing both sides of the battery-mounted fuse block with a math channel (Ch3 - Ch1) revealed a massive 1.88V voltage drop directly across the fuse terminal itself. Wiggling the cable caused the reading to jump right back up. When we unbolted the lug, the root cause was obvious: someone had over-torqued the nut in the past, fracturing the internal fuse element. It could pass a 4-amp test light, but the moment the high-draw fan motor demanded inrush current, the voltage crashed and the smart fan controller shut itself down on fail-safe. Popped in a replacement fuse, watched the current ramp smoothly on the scope, and the fan is back in business! Always load-test and check your voltage drops! #justwingingitgarage #carrepair #launchx431 #micsig #mechaniclife

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Friday 04 September 2026 18:27:31 GMT