Battery Light

15

Asked by Mar 07, 2017 at 08:36 PM about the 2008 Ford F-150 Lariat SuperCrew 4WD

Question type: Maintenance & Repair

I have a 2008 Ford F150 that will not start because of a bad ground on the starter relay. Needless to say, I still need to drive around so I've been starting the truck by applying voltage directly to the starter from the battery. The truck starts and runs fine but recently the battery light came on while I was driving. It stays on for about 30 seconds and then goes away. Why would the battery light come on? Bad battery/alternator?...

I tested the truck today and the battery seemed low with about 12.15V before starting but the truck started right up (battery is less than a year old). The voltage went up over 13V and stayed over 14V for the next 10-15 minutes. I had the hi-beam headlights on, the a/c and the radio. I could tell the alternator was charging the battery and just before 10 minutes in the battery light came on but there was no change in the voltage reading. It was still 14.2-14.4V but I DID hear a change in the noise. It sounded like the engine slowed down or got quieter momentarily before the light came on. My question is why would the battery light come on? If my battery and alternator are good what other possibilities could this be? Why would the light come on if the battery is reading 14.2-14.4V?

4 Answers

87,235

It may be that the battery is low. Try charging the battery back up to the full charge of 12.7 DCV, 12.5 DCV at least. Also look at the condition of the serpentine belt. It may need to be changed along with a new belt tensioner. Belt may be slipping due to the call of the amount of charge the battery needs.

7,485

the starter relay is the solenoid , thats what you're heating up when you jump it from the batt. The ground for that "starter switch" is the starter bolted to the motor block .there may be some kind of short down stream from the batt. because you had good voltage there but the batt light came on , thats what I'm thinking .12.5 volts is good for a batt. at ease , let us know what happens .

15

The PCM was bad.

7,485

Cool , if you took it to a garage they might have toyed around and still not found the problem , and of course they would have charged you , Thats why we work on our own .

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