Most propably the pickup is dead, meaning that adjacent pickups are picking the "low" sound. The pickup iron core gets rusted in humid environment (garage, outdoor, etc) and the very thin copper coil can be broken .. closest rounds to the core. Remove the pickup. Take 2 pencils, attach the pickup to one pencil with sticky tape. Unwire the copper coil to the other pencil (drill or screw twister is great help here). After almost done, you will see that the wire was broken. Fix the broken wire and re wire it back round the core. 15 min and you are done.
Good luck
If you have multimeter, measure the coil first to avoid possible unnessary work.