Skip the auto shop - Our mechanics make house calls

Q: Overcharging 18volts +

asked by on

My truck overcharges the batteries. I changed out my alternator,I even took it to a shop that deals with electrical issues.I was told the ECU in my truck has a internal voltage regulator they tried bypassing it with a external one still no dice! Please help

My car has 350000 miles.
My car has a manual transmission.

The shop was correct about how the ECU controls the field current of the alternator which will cause the alternator to charge the batteries. If the wire on pin 57, the dark green with orange stripe wire at the ECU, is getting battery voltage then it is normal. If not, then it is broken and needs to be repaired.

You should then be able to disconnect ECU pin 20, the dark green wire, and the alternator should stop charging. If the alternator does not stop charging, this wire should be checked between the ECU and the alternator field for grounding in between. If the alternator charges when you ground the dark green wire, and doesn’t charge when you don’t connect it to anything, then the wire is not grounded. Check to make sure the alternator is grounded. The ground is near or below the a/c compressor.

If the wires listed all check out to be okay, and the alternator will turn the charge with the dark green wire on and off, you will need to have the ECU replaced. If the shop put in an external voltage regulator then it should of worked if it was installed correctly. If the alternator overcharges the batteries even after the field circuit is disconnected, then the alternator is shorted and needs replaced.

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

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: wont start and we byassed the clutch saftey switch and it still wont start what next

Hey there. You have a starter relay on the left of the engine compartment that sends power to the starter solenoid when you go to crank it. This is the only part you have not changed. If you would like...

Q: Joe I am having an issue with my 1997 Dodge Ram 2500 5.9L Cummings motor, motor would not start I changed fuel filter it started r

Hi there. It is possible that the fuel filter change may be the cause of your hard to start issue. If the fuel filter is either the wrong size or was installed backwards, it would cause a restriction of diesel...

Q: Power steering not working.

An engine that has a large oil leak runs the risk of internal failure and a very expensive bill, I would not drive the car any further until the leak has been addressed. Sometimes and oil filter can come loose...

Related articles

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...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.