Looking for a bit of help.
In the spring my 2011 Evo X GSR got a check charging system code. I checked the voltage of the battery and got a volt gage. My car is reading too much voltage. It is off and on. Ive seen it get as high as 16 volts. And it normally goes between 14.7-15.4.
9 year old car on original battery and alternator.
First I replaced the battery which helped for a month or so.
Then it started again so I replaced the alternator.
Battery voltages were great for a short while again. 14.2-14.7 steady.
Now it seems like every 2nd start up the battery light comes on and stays on. Sometimes voltages are reading good. 14.6. Sometimes reading high. 15.3.
Im hoping this isn’t an ECU issue now from over voltages for a while.
Possibly a bad relay?
Has anyone had a similar issue?
Ive visually gone through lots of the wiring looking for burnt or pinched wires. Everything seems good.

 

The voltage regulator is internal to the alternator. Are you running some large stereo / electrical loads that could be cooking them?

 

Nope.
Stock basic non touch screen stereo.
The only thing electrical I’ve added is Boost and AFR gauges. But those have been in for years now and I’ve only had this start to happen last spring ish.

 

Remanufactured alternator or OEM replacement? Also might want to check battery voltage after you shut off the car then again say the next day before you start it. Record the difference. Should stay 12.6V or above with everything off. Maybe you have some current drains.

 

I replaced the alternator with an new aftermarket.
I checked the voltage before I started it up just now. 12.6.
Cold start voltage once turned on was 14.7.
I watched for a bit and the check battery flickered only once but voltage stayed steady.

Im checking to see if it only happens while defrost or the compressor is running. It’s almost always on defrost as I live in Toronto and we’re on month 6 of cold weather.
Ill make sure it’s off and check for the next few days. It’s not my daily so I only drive it maybe a couple times a week during the cold months.

 

check your electrical connections, it sounds like your getting voltage drop across something.

 

So I found the issue. Just haven’t found a fix yet.
The battery is reading 14.6 on startup and the s terminal from
the battery going to the alternator is reading 10 volts. Less if I put on the a/c.
ECU is reading this and trying to put out more voltage thinking the battery is low.
In the wiring diagram it’s saying it’s supposed to be the same voltage. All the wires look ok and everything is wrapped tight in tape and conduit.
Easy fix is to run a wire straight from the battery to the S terminal at the alternator I guess.
but I really want to know what’s drawing or limiting the power.

 

Glad you traced down the culprit. Disconnect both ends of the straight piece of wire and check with an ohmmeter. My guess it has turned resistive. Remove and replace.

 

So the car drives fine now but I still get random check charging codes, abs, and 4 wheel drive. Flickers on and off. Also I see a battery light flicker when in full WOT.
My volt gauge is reading fine now tho since I ran a new wire straight from the battery terminal block.
I really think my ECU is the issue. I’m looking for a used one right now because I already replaced the battery and the alternator twice.

 

I’m going to update this despite being a 5 year old thread, incase somebody, somewhere, runs into a similar issue.

I purchased this Evo, very heavily modified, with a blown engine off the OP in the fall. When I picked it up, he let me know about the alternator issue and wire that he ran, as well as the draw the car has.

I finally got around to replacing the engine and returned the car back to 100% stock. The first hour that it ran (to burp the coolant) the battery almost exploded. Turns out the car alternator was charging at almost 16v the entire time with no warnings anywhere on the dash.

With the wire the OP ran to the battery terminal from pin 3 on the alternator plug (which bypassed pin 62 on the ECU), the car would charge 15.5-16v. With it disconnected it wouldn’t charge at all, but still no charging warnings on the dash either for too high or too low voltage.

I checked continuity across all 4 wires on the plugs and determined pin 2 on the alternator plug, which should go to a 7.5A fuse (number 5 in the fuse box under hood) had a break somewhere along the line from the fuse box to the alternator. I think this was the original problem, and the wire the OP ran which removed the ECU’s control of the alternator regulator, was just a bandaid so it would charge.

I repaired the break on the pin 2 to fuse box, and reverted pin 3 back to factory wiring so the ECU can control the regulator properly via pin 62. The car now charges at a healthy 14.3-14.5V, idling and under load with revs.

so if anybody in the future has something like this, check your wiring. I work on these for a living but it’s the first time I experience something like this. Here’s a rundown on a quick continuity check anybody with a multimeter and 15 min of time can do, to ensure the wiring is ok:

Alternator pin 1 > ECU pin 60
Alternator pin 2 > underhood fuse box, fuse #5 which is a 7.5A
Alternator pin 3 > ECU pin 62
Alternator pin 4 > ECU pin 61

 

I believe I have this same issue. I have 12v at connector b-111 pin 2 while connector a-39 is unplugged. When I plug in connector a-39 the voltage drops to 1-3v. Ohm checked between connector a-39 and b-111 on pin 5 at a-39 and pin 2 at b-111. I have nothing. I can run a wire from battery terminal to alternator and light goes out. Did you pinpoint exactly where the break is in the wire?

 

Sorry to hear you're dealing with something similar. The break on that car was somewhere in the lower harness, between the intake manifold heading down to the alternator. The upper portion was fine leading to the fuse box. I did not unravel the entire harness to chase it. Rather, kept what I knew was good and just ran the same color, same gauge wire to a new plug for the alternator. for the lower portion of the harness where the break would've been.

To this day the car has no charging issues, and no drainage issues after the repair.