Where does ECU get system voltage?
- Thread starter drallan
- Start date
You know what, I never considered that the alternator wasn't producing the correct current, just assumed that if the voltage was good the alternator was good. But checking the amps its putting out is a good idea. That could be the issue.
Thanks for the suggestion.
I don't have a designated ammeter, assuming a standard household multimeter should work? I've got a few so I could set it up like the FSM suggests (with a spare set of hands or 2) to measure voltage and amp output.
Depending on how long my cables are I might disconnect the big cable (cable B) off the alternator, I think it has a ring terminal, and use alligator clips on the multi-meter to clip onto the post of alternator w/ one and ring on the other to complete the circuit. Or I can run out and grab some fresh cable and make up a new one to run it to the battery.
AuSeeker
Elite Member
In the first reply in this topic, I suggested the alternator could be going bad, you either didn't read my reply or you decided not to check the alternator and or I couldn't possibly be correct. :noidea:
Runnin on E
Member
Also as Auseeker suggests there are other previous comments that could help you (free charge sys test from the auto parts store?). Why don't you reply back here after you have tried all the procedures offered, and let everyone know what caused your issue.
I don't disagree alternator could be going bad. My understanding of electronics is limited. My go to cliche is enough to be dangerous and not enough to be useful. As I stated in a few of my replies, I'm open to the idea that my assumptions have been wrong the whole time.
Initially I was trying to diagnose why I was seeing a difference in voltage on my OBDII scanner and my multi-meter. Now that I have identified my OBII as being bad and am getting consistent readings both inside and out, I've moved on to the next step of my diagnosis. Might not be the most efficient method, but I'm working with what I have with the time available to me.
Other assumption I've had, and again could be wrong, is that mid 13+v (while less than ideal) should be sufficient to not have a persistent battery light. Or at least have an intermittent light or go off every now and then when I get a spike higher in the 13s.
I thought by testing the voltage with a multimeter at the cables was "testing" the alternator. If there is a better way or alternative way to test it I am open to the idea.
In my past experience when an alternator goes, it usually goes pretty quickly, again could be wrong. Mine has been this way for 6months now, keeps battery charged fine, car starts without issue (even in current string of below freezing temps). All the cables and grounds I can see look good, so I was trying to see if there was another wire or fuse somewhere I wasn't aware of that I should check.
I wasn't trying to dismiss your idea, just needed a little more than the alternator is going bad. Again, not saying it isn't, just trying to diagnose before replacing.
Appreciate the help.
Honest question.
Is it preferred on this forum to only post back after finding a solution, or throughout the diagnosis? I don't post often as I've had minimal issues that require a post, but personally get frustrated by the questions with no resolution. So I thought walking through my process might spark something in someone in the future. I'm just a regular DIY guy on a budget trying to keep his car alive as long as possible. I've seen both, long threads that are hard to follow (maybe this is one of them), and short threads with no outcome.
Initially I was trying to diagnose why I was seeing a difference in voltage on my OBDII scanner and my multi-meter in the engine bay. Now that I have identified my OBII as being bad and am getting consistent readings both inside and out, I've moved on to the next step of my diagnosis. Might not be the most efficient method, but I'm working with what I have with the time available to me.
I will / can take it to an auto store and have them test the alternator. Part of it was that I want to try and learn more about the electrical / charging system and diagnose the problem myself. Understand what the thresholds are that set off the "battery light", where the ECU gets those values, read those values myself, then determine whether or not the alternator is the problem or something else.
Especially as it isn't currently effecting my daily driving or left me stranded (at least not yet).
Appreciate the help.
I will report back once I have more information or something new.
There are a couple of other alternator plug threads so I'll continue over there, but my plug only has 3 wires, not the 4th lower right ECU wire. So when I get a chance I'll try to figure out which one feeds the ECU. Hardest part is access to the alternator side of the plug while the engine is running, especially without a lift / garage, not to mention it has been stupid cold.
Might try to find a matching plug online and make up a test harness so I can have better access to the wires. Other than check engine light and maybe a few other codes, shouldn't be any problems running unplugged?
