Check brake system message

[Allegretto]

I have a 2007 Taurus and for some odd reason I get a message saying to check the brake system. Its accompanied by dimming dash lights and symptoms of a bad alternator. I'm suspecting the battery (its from 2009). Sometimes the issue goes away and when I drive and get the car above 1300 rpm it will go a way until the next stop light/sign. Any ideas suggestion and info are greatly appreciated thanks in advance guys!

[shorod]

I think you are on the right track, it does sound like an issue with the charging system. Your battery is likely due to be replaced, but confirm the alternator is also working since putting a new battery in with a bad alternator could damage the new battery in short order.

If you don't have a multimeter to test the charging system at home, many of the chain auto parts stores or dedicated battery stores can test your charging system if you drive to their store, and most offer the service at no cost. I have experienced more than once where their test claimed a battery was good even though it wasn't, but I haven't yet found the test to fail a system that was good.

-Rod

[Allegretto]

As it stands I do have a multimeter from my job. What places on the charging system should I check because I had AAA test the battery and it did test good. He said there may be a bad ground somewhere(?) I'll get right on that tomorrow morning though

[shorod]

You would test at the battery and near the battery. I'd suggest you start by checking the voltage when the starter motor is engaged with the multimeter probes on the battery cables directly. If the voltage drops to something below 10.5 volts DC (VDC) when the starter is engaged, then move the probes to the battery posts and see if you get the same readings or if the voltage is higher when the starter is engaged. If the voltage is noticeably higher, then you probably have a poor connection at the battery.

If the initial measurement above yields a reading higher than 10.5 V, then move the black probe to a clean, good ground and repeat the test. If now the voltage drops well below the measurement at the battery, then you have an issue with the ground connection.

If none of these measurements show anything significant, then repeat the measurements but with the engine running and make sure in all cases the voltages are pretty consistent with one another and the Engine Running voltage is between 13.8 VDC and 14.4 VDC.

And, keep in mind, the above applies pretty well to vehicles that are several years old, but starting around the mid-2000's for some manufacturers (not so much Ford) and rather common today, the charging systems are "smarter" and only charge to the minimum amount necessary given the State of Charge (SoC) on the battery and requested load to improve fuel economy. Therefore the Engine Running voltages at times may not exceed the battery voltage, even on a properly working charging system. In those systems you really need a higher end scan tool to determine what the state of the charging system is.

-Rod

[Allegretto]

Awesome I'm gonna test it soon as i get off work tomorrow

[Allegretto]

I checked it with a multimeter and it stayed at about 13.6-14.3 volts. I think its the battery because since the temps went up a bit the problem has went away.

[shorod]

Did you measure the minimum voltage while the starter was engaged? The 13.6-14.3V readings you mention were no doubt while the engine was running.

If your multimeter has a "Min" setting, that might help capture the lowest voltage while the starter is engaged.

-Rod

[Allegretto]

Yes I did check it while the vehicle was starting, it dropped to 9.8. I had to set my phone up to record it because I was solo but I have video. I had AAA come out and test it and it said "phase open" (?) I have no idea what that means

[aleekat]

Originally Posted by Allegretto

Yes I did check it while the vehicle was starting, it dropped to 9.8. I had to set my phone up to record it because I was solo but I have video. I had AAA come out and test it and it said "phase open" (?) I have no idea what that means

Phase open generally refers to alternator winding issues.

[Allegretto]

I took it to auto zone (yes I know, but time was of the essence) and sure enough the alternator was fried

[aleekat]

Thanks for the post back.

[shorod]

Hopefully a new alternator takes care of the issues. Thank you for following up on your thread. You have two independent sources/tests that point to a faulty alternator, so that's a pretty good sign it's an issue. The voltage measurements you posted in post #6 above don't necessarily support a bad alternator, but I didn't have you try measuring AC voltage which would help identify a bad set of diodes or a missing phase.

-Rod