Symptom guide · Glass Box Diagnostics
A slipping belt means a weak tensioner, a glazed belt, or an accessory bearing starting to drag. When a belt finally quits you lose three systems at once: the alternator stops charging, the water pump stops circulating, the power steering goes stiff — and on most cars the overheating starts within minutes. The morning squeal was the invitation to fix it for the price of a belt and tensioner.
Belt dressing — the industry's duct tape, loud for a week, slippery forever. Or an alternator replacement, because a slipping belt also produces a low-charge voltage that reads like a dying alternator. Same symptom, opposite culprit, $700 apart.
Typical guess-and-swap cost: $600–$900 (alternator) when the actual fault was a $150 belt-and-tensioner set — or a $40 idler pulley
Belt off the tensioner: every pulley spun by hand for roughness and side-play; tensioner travel measured against spec; charging output at the battery watched on the scan tool while the noise is present to confirm or rule out slip. A belt that measures tight and still squeals means something is being held back.
Codes this symptom commonly sets
We come to you — Canyon Lake, San Antonio & Austin. Written report with root cause — see a sample.