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?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. Overcharging 18volts +

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: What is The Cost of Parts to Replace a Bad Exhaust Intake Valve on a 1995 GMC Sierra? How Long does it take to complete job?

Hi M.H. Thanks for contacting us tonight. Unfortunately, this is a service that our mobile mechanics are unable to offer. This type of job should be completed at a local engine shop, as removing valves will require special tools in...

Q: Where is the ignition switch harness located? Also, what color wire and gauge are the ignition accessory wires for this vehicle?

Hi and thank you for contacting YourMechanic about your backup camera installation. The ignition switch harness is located inside the steering wheel column on the left side. If I'm not mistaken, the ACC wire will be an 18 gauge pink/yellow...

Q: Van overheats

Hello. Yes there are two key things that I recommend you or your technician check. Check the hoses, radiator, and engine block for clogging. A clog in those components will restrict the coolant system from being able to circulate. Also,...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
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.