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2009 GMC Acadia - TPMS Always Target Same Tire

2009 GMC Acadia, left front tire always low even with regular rotation at oil change. When I fill it or they fill it after rotation, it loses several pounds relatively quickly; the other three tires maintain correct pressure, lose a pound or 2 over time but certainly normal.

I purchased used in october (76k mi). Car has had 3 rotations. It does have tire pressure monitoring. Tires in good shape, so far as I can tell the rims are in good shape. Even if something was up with rim or valve stem, I’d think the issue would have stayed with that tire as it was rotated around the car. Any advice?

Unrelated but just for full info, in solving a surging / stammering loss of power at highway speed on incline (turned out to be 2 coils), my warranty covered replacement of 2 valves, 2 coils, full transmission replace (with fluids, alignment etc – the coils code wasnt popping up yet so lucky me), cv joint (spotted slung grease when looking for other issues). The larger Replacements and fixes have been much more recent, this pressure problem predates them and has persisted despite all rotations and alignment.

I can’t explain this weird behavior, but it wouldn’t hurt to spray soapy water on all the tires and valve stems and look closely for bubbles. If you hit the spot where several pounds is being lost quickly, you’ll definitely see bubbles, although it’s harder to cover the whole tire when it’s still on the car.

it’s possible that whomever is doing the rotations isn’t resetting the TPMS, and you are inspecting the wrong tire.

do as @lion9car suggests and check all the tires.

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^^This. OP, have you manually inspect the pressure of that front tire? I’m guessing the vehicle is still seeing that (one) defective tire as the front left one, even though it keeps moving around the vehicle.

What would be weird is if you physically measured the front left tire pressure after each rotation, and it was always a few pounds low (regardless of which tire was on the front left wheel). But I’d bet money that that’s not the case here.