Skip the auto shop - Our mechanics make house calls

Q: Battery light comes on after starting and stays on running the battery down

asked by on

I changed alternator and PCM and the problem still exists. I checked the wires and continuity from the PCM to the alternator and they are good. alternator will not charge even though it is new. I have been told there is a bad wire or a shorted wire. All fuses are good. ???????

My car has 216000 miles.
My car has an automatic transmission.

You need to have the alternator’s large red terminal from alternator to the starter tested for proper battery voltage. The orange wire coming out of the alternator should have battery voltage at all times. This is the volt sense wire and is fused by a 10amp fuse in the engine fuse box. The last alternator wire , a small red one, goes to the PCM and this is the wire that the PCM uses to control the alternator output. The PCM should be scanned as well as the data from the instrument cluster to see if the instrument cluster is causing the problem by not giving feedback voltage to the PCM.

You may have a defective cluster or you’ll need to disconnect the connections at cluster and PCM. Then add dielectric lube to connector pins and seals. This will help stop fretting corrosion in connectors. This can potentially cause high resistance in connections and cause the problem you’re having.

If you need some help with these checks, consider YourMechanic, as a certified technician can tests these components and diagnose the issue with your Battery Light.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  • Home
  • Questions
  • Battery light comes on after starting and stays on running the battery down

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: The ABS, Trac Off and Airbag light came on after a battery change. No lights before with engine running

You may have damaged the systems when you disconnected and connected the positive cable to the fuse block last and not using the battery ground. I would recommend disconnecting just the battery ground and then leave it off for ten...

Q: Replaced blower motor resistor on a 06 honda accord 4.2l. Only blows on high regardless of what speed I set it on

Hi there. Assuming the original problem was no blower motor speeds at all, leads me to believe that the replacement blower resistor may be your issue. High blower motor relay stuck closed would of given you high speed only, prior...

Q: Car will not stay on after starting it sometimes

Hello, I'm curious if there are any problem codes set (they may or may not cause the Check Engine light to illuminate). If so, these will be helpful. Most auto parts stores will read these for you for free. I...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...