Driver-side Amp Research power step stopped deploying last Tuesday. Motor whirred but nothing happened. Dealer said $600 for a new motor assembly.
I grabbed a $12 multimeter from Harbor Freight instead. Popped the motor connector — 12.4V at the harness, good. Motor itself: 0.8 ohms, within spec. But the gearbox output shaft had zero resistance when I turned it by hand. Stripped planetary gear inside.
Found a replacement gear kit on Amazon for $34. Took 45 minutes to disassemble, clean, and rebuild. Works perfectly now. Been 3 months and zero issues.
Lesson: don't throw parts at power steps. The motor is almost never the problem. It's the gearbox or the linkage. Multimeter first, then parts.