Electrical issue driving me nuts

[ChipG]

I'm at my wit's end on this issue. I've been chasing it for awhile and posting on M6G, but thought I'd see if this is something more common in tracked vehicles via heat-fried or vibration-affected components. Recap:

Behavior: "Charging System Service Now" light pops on within about 5 seconds of startup, stays on steady for the remainder of the time the vehicle is running. On one drive (unclear what made this drive different), the center stack, HVAC, and other power shut down, and AdvancTrac disabled.

Checks and attempted fixes:

• Voltage meter on dash typically jumps up to ~15.2V after startup, settles into mid-14V range steady. On the one drive, voltage meter went completely crazy.
• No voltage drops anywhere in the fuse box.
• Forscan shows slight difference between battery voltage requested and system voltage (14.56V vs ~14.8V - 14.9V respectively). This is after pigtail and battery replacement, before alternator replacement.
• Visual and manual inspection of wiring harnesses, grounds, and connections that I can find shows no obvious issues. Connections are tight, non-corroded.
• Replaced the alternator voltage regulator pigtail. No change in behavior. This was the cause of my problem last year (much more sporadic on/off/on error message) and I replaced it then, fixing the issue.
• OEM battery read low after sitting. Replaced the battery with a fully charged AG ATX20-HD, performed the BMS reset several times (both non-Forscan and Forscan versions). No change in behavior. (To be clear, the one time the system went crazy was after battery replacement).
• Replaced alternator. No change in behavior, though I haven't driven the car around since this, just driveway start and idle testing.

At this point, the starter is relatively new. Battery is new. Alternator is new. All seem to function well (starts easily, battery holds voltage, alternator puts out proper voltage). Alternator pigtail is new. I'm not sure what else to do. The only other info I've found is a post here indicating that there is a main wiring harness that tends to fry the alternator. I have no other ideas than trying to replace that as well.

Any ideas? Specific connectors grounds to check? Specific Forscan checks? Specific voltmeter checks? Otherwise, I will indeed throw another part at it and put the harness in. If I have to go to a dealer, I can try that, but my confidence is low in that path. They refuse to diagnose without all OEM parts (so I'll have to reinstall the alternator and the possibly-failing OEM battery), and last time this happened they failed completely to figure out the issue (though different dealer). If they just go fishing, the labor and parts are on my dime with no guarantee of a fix. My suspicion is they will likely want to replace everything I've already tried with new OEM parts and labor, which is a waste of time and money.

This issue is driving me nuts, and I have a race this weekend.

 

[ChipG]

Additional updates:

• Every time I try to drive the car now, within 5 minutes the voltage goes crazy, spikes as high as 17V, the center stack powers down, and AdvancTrac disables.
• I disconnected the current sensors to disable BMS and it made no difference in behavior.
• DTC code is P0625: Generator Field/F Terminal Circuit Low

I have the OEM battery charging now to make sure it's fully charged and will try putting it back in tomorrow to see if anything changes, but the behavior still feels like a voltage regulator issue. I'll take yet another look at the pigtail again tomorrow as well. I don't know what else to do other than replace the whole engine harness.

 

[blacksheep-1]

See if you can barrow another alternator and see if that is the issue before going through the harness, also check every ground on the planet. These cars are moron reliant on electronics and we've been down this road with the Gt4 car. I'm far from an expert on this because at the races we're whipping crap apart and changing it out as fast a spossible. But the funky voltage seems to me to be the red flag and I'm saying alternator.

 

[ChipG]

See if you can barrow another alternator and see if that is the issue before going through the harness, also check every ground on the planet. These cars are moron reliant on electronics and we've been down this road with the Gt4 car. I'm far from an expert on this because at the races we're whipping crap apart and changing it out as fast a spossible. But the funky voltage seems to me to be the red flag and I'm saying alternator.

I did change the alternator to no avail, which is what has me looking at the harness.

 

[JP X]

Based on my experience, your problem might go away once you put a standard battery in. My AG lithium battery made everything go haywire after 14 months. Stuck a Wal-Mart battery in…all the problems disappeared.

 

[ChipG]

Based on my experience, your problem might go away once you put a standard battery in. My AG lithium battery made everything go haywire after 14 months. Stuck a Wal-Mart battery in…all the problems disappeared.

I'm going to try and see, but the problems started before the AG battery with an OEM battery in place. The AG was because I thought the OEM battery might be on its way out.

 

[JP X]

I'm going to try and see, but the problems started before the AG battery with an OEM battery in place. The AG was because I thought the OEM battery might be on its way out.

Ah. Then my theory doesn’t look like it will hold water. Good luck. As we say at work: “the problem‘s in them there wires”

 

[ChipG]

So, some progress. I swapped the fully charged OEM battery back in. The "Charging System Service Now" notice still pops up within 5 seconds, but in ~5 minute test drives with and without the current sensors in place the system didn't go nuts and shut down as it had very quickly on the same drives with the AG battery. So, perhaps I'll at least be able to run this weekend while I chase the wiring issues. It remains to be seen whether the AG will cause any problems with the rest of the system healthy.

Later today - fully checking (removing/cleaning) all the grounds, and re-checking the alternator pigtail.

 

[ChipG]

Still no more progress.

• I reinstalled the OEM alternator, cleaning all the contacts and continuity checking all 3 wires on the pigtail.
• I cleaned and reattached both grounds on the passenger side strut tower and both grounds underneath the air filter box.
• I tested with my truck battery, which is significantly larger than the GT350 OEM battery and which is less than a year old.
• I was unable to locate a ground to the engine block on the passenger side anywhere near the engine mount or starter. If there is one there, I'd love assistance finding it.

Behavior is unchanged after any of those tests - the error message pops up within 5 seconds of starting the engine. I now have the OEM battery, alternator, and starter back in the car, all less than a year old. I've checked every ground, wire, and connector I can find with multiple checks and a replacement on the alternator pigtail. I welcome suggestions on other ground locations to check.

At this point it HAS to be a wiring issue somewhere in the harness I would think. Something cooked or vibrated to oblivion. I can't think of anything else I can do besides:

1 - replace the whole engine harness (myself or pay to have it done)
2 - take it to a dealer and watch $$$ fly making them chase it.

 

[Stan Whitney]

Did you get to do the bms reset with forscan after the oem style battery and alternator re-install? I may have missed it in the updates.

 

[ChipG]

Did you get to do the bms reset with forscan after the oem style battery and alternator re-install? I may have missed it in the updates.

I did not, but the BMS only thinks the battery is 1 day old anyway after the previous resets.

 

[TMSBOSS]

Is the car still under warranty?

 

[ChipG]

Not bumper to bumper, just powertrain, so electrical is not included. Not that it even matters much - last time I had this issue it was the alternator pigtail. The dealer couldn't figure that out. They replaced PCM, battery, and alternator, tried blaming my starter, OBD dongle, and eventually "fired" me saying they couldn't figure it out and suggesting I try someplace else. I diagnosed it, bought a $17 pigtail, and fixed it in half an hour in my driveway. I'll just say my confidence in a dealer figuring it out isn't high...

 

[TMSBOSS]

I hear ya. Going to Some dealership shops is like opening a box of chocolates. You never know what you will get until you take a bite.
I wish you were a bit closer to me. I have a connection which has access to the factory service software. I grab his laptop and work with it in my shop. Happy to help if I can.
good luck.

 

[Egparson202]

@ChipG - Did you solve the mystery? Whodunnit?

 

[ArizonaBOSS]

Yes, any further updates?

 

[ChipG]

I have bought a new engine wiring harness but haven't yet installed it - will keep y'all posted if that works.

 

[Egparson202]

I have bought a new engine wiring harness but haven't yet installed it - will keep y'all posted if that works.

This triggered a memory. I feel like there were some posts a few years back about a company that modified wiring harnesses. I think the term was “hardening “. Anyone recall that?

 

[ArizonaBOSS]

This triggered a memory. I feel like there were some posts a few years back about a company that modified wiring harnesses. I think the term was “hardening “. Anyone recall that?

Home

Precision Race Services, Inc.

www.p-r-s.com

These guys would make the motorsports harnesses for the race cars and/or convert an OEM harness to Deutsch-style connectors and potted (epoxy filled for vibration resistance) sensor connections.