The alternator charges the battery and powers everything electrical while the engine runs. When it fails, the car runs on battery alone and stops within twenty or thirty minutes. AutoTech Clinic tests charging output and replaces alternators at our shop on Michigan Ave in Dearborn, usually the same day.
We test output, ripple and the control circuit before replacing anything, because a charging fault can also come from a broken belt, a corroded ground or a computer controlled alternator being commanded off.
- How Long
- About 1.5 to 3 hours on most vehicles.
- Same Day
- Usually finished the same day.
- Vehicles
- Foreign and domestic, cars through trucks.
Signs You Need Alternator Repair
- The battery or charging warning light comes on while driving
- Headlights dim at idle and brighten when you rev
- The car dies shortly after a jump start
- A whine or growl from the alternator that follows engine speed
- Electrical accessories behaving oddly or resetting
- A burning rubber smell from a slipping serpentine belt
What We Do
- 01
Measure Output Under Load
We check charging voltage at idle and with the lights, blower and rear defrost on, which is where a weak alternator shows itself.
- 02
Check Ripple
A scope reading shows whether a diode inside the alternator has failed. That produces odd electrical faults long before the car stops charging completely.
- 03
Inspect Belt and Tensioner
A glazed belt or a weak tensioner lets the alternator slip under load, which looks exactly like a failing alternator and costs far less to fix.
- 04
Test Grounds and Control
On computer controlled charging systems we check the command signal, because the alternator may be working correctly and simply not being asked to charge.
- 05
Replace and Verify
After fitting we confirm output across the full load range, check the belt alignment and recheck battery condition, since a deeply discharged battery is often damaged.
Why a New Battery Often Comes With It
When an alternator fails, the battery runs the car until it is flat. Deeply discharging a lead acid battery damages the plates, and a battery that has been run completely flat once or twice rarely recovers full capacity.
We test the battery after fitting the alternator and tell you honestly what it reads. Sometimes it is fine. Often it is not, and fitting a new alternator to a damaged battery means the warning light comes back.
Smart Charging Systems Confuse Simple Tests
Many late model vehicles vary charging voltage deliberately to save fuel, dropping it to around 12.5 volts while cruising and raising it when braking. A quick voltmeter check at the battery can read low and look like a fault when the system is working exactly as designed.
We read the charging command from the control module alongside the measured output, so we know whether the alternator is failing or simply doing what it was told.
What Affects the Cost
We quote your vehicle specifically after inspecting it, because these are the things that move the number up or down:
- Alternator cost, which varies widely by vehicle
- New versus remanufactured units
- Access, since some alternators sit low and require removing other parts
- Serpentine belt and tensioner replaced at the same time
- Whether the battery was damaged by running flat and also needs replacing
Call (313) 277-7200 with your year, make and model and we will tell you what to expect before you come in.
Why AutoTech Clinic
AAA Approved
An inspected facility that has to meet AAA standards for equipment and training.
Photos First
You see what we found and approve the price before anything is taken apart.
Same-Day Service
Parts on hand for the vehicles we see most, so you are not waiting on a delivery.