# Charging System Test in Upland > Battery light on or headlights dimming at idle? Route 66 Auto Repair in Upland tests alternator output, belt grip and charge wiring under real load. Source: https://route66autorepairshop.com/electrical-services/charging-system-test Updated: 2026-09-17 Business: Route 66 Auto Repair, 1775 W Foothill Blvd, Upland, CA 91786, (909) 608-7699 Hours: Monday to Friday 8 AM–5 PM, Saturday 8 AM–2 PM, Sunday closed **TLDR:** The battery light points at a **system**, not a part. We test **belt, output and wiring** under load to find which link failed. When the battery light comes on, Route 66 Auto Repair in Upland runs a charging system test before anyone buys an alternator. The test checks the whole path that refills your battery: the belt that spins the alternator, the alternator's output, the charge wire and the grounds. A fault in any of them can light the same warning. Knowing which one saves you from paying for a part you did not need. ## When should you get the charging system tested? - The battery or charging warning light comes on while driving - Headlights dim at idle and brighten when you rev - A new battery keeps going flat - A squeal from the belt on cold starts or with the AC on - Gauges or the radio act oddly when many accessories run ## What does a charging system test measure? First, charging voltage at idle and at a higher engine speed, with lights, blower and rear defrost all on. That full load is where a tired alternator gives up. Next, the belt: its grip, wear and tension, since a slipping belt cannot turn the alternator fast enough. Then voltage drop on the charge wire and the alternator ground, because a corroded connection can waste output before it reaches the battery. On many cars we also look at ripple, a small AC pulse on top of the DC charging voltage. Too much ripple can point to a failing diode inside the alternator. Charging voltage has a well-established window. Most 12-volt systems are expected to sit somewhere between roughly 13.5 and 14.7 volts at the battery with the engine running, higher on a cold morning and lower once everything is warm, and a reading outside that window in either direction is worth chasing. Some newer vehicles vary output deliberately to save fuel, so the range in your vehicle's service data, not the general figure, is what a result is judged against. ## Our charging system test process 1. **Battery first:** A charged, healthy battery is needed for a fair test, so we check it first. 2. **Belt check:** The belt is inspected for glazing, cracks and tension, and the tensioner is checked. 3. **Load and measure:** Output voltage and current are measured at idle and higher speed with accessories on. 4. **Wiring check:** Voltage drop is measured on the charge and ground paths. 5. **Report:** We tell you which link failed and give you a written estimate for the fix. ## What's included - Battery state of charge check - Drive belt and tensioner inspection - Output under full electrical load - Charge wire and ground voltage drop - Code scan for charging-related faults - Results on the repair order ## What happens if the test fails? If the alternator is the cause, [alternator testing](https://route66autorepairshop.com/electrical-services/alternator-testing) confirms it on its own before we quote [alternator repair](https://route66autorepairshop.com/electrical-services/alternator-repair). A worn belt leads to [alternator belt replacement](https://route66autorepairshop.com/electrical-services/alternator-belt-replacement). On newer cars where the computer controls charging, we may also run a [battery charger system test](https://route66autorepairshop.com/electrical-services/battery-charger-system-test). ## Need it now or later? **Need now:** - Battery light on while driving - Dimming lights at night - A burning rubber smell from the belt **Need later:** - A light belt chirp on cold mornings with normal output ## How pricing and timing work The diagnostic fee is stated at the counter before testing and applies to the approved repair. Many charging tests fit the same day when the board allows. Call [(909) 608-7699](tel:+19096087699) before driving over, and keep accessories off on the way if the light is on. AAA members get 10% off parts and labor, up to $75. ## Aftercare If the battery light returns after a repair, pull over when safe and call us. Comebacks go to the front of the line. ## Frequently asked questions ### Can I keep driving with the battery light on? Only a short distance. The car is running on battery power alone and will stall when it runs out, often along with power steering on some models. Head straight to us or a safe spot. ### Why test the battery for a charging problem? A dead or shorted battery can make a good alternator look weak. Testing both keeps the result honest. ### Can heat affect charging output? Yes. Alternators produce less as they get hot, which is why a marginal unit often fails in summer traffic on the 210. --- Call (909) 608-7699 or visit https://route66autorepairshop.com/contact for a written estimate.