Hello everyone,

About a month and a half ago I replaced the clutch and after I finished, the battery light came on while I was driving home. When I parked, I checked the alternator output with my voltmeter and got about 12.20v while the engine was running.

I replaced the alternator and I have the same problem. The battery is less than a year old. There's no check engine light on, only the battery light comes on after the engine runs for half an hour or so. I checked to make sure I reconnected all the grounds after I finished the clutch job and didn't find any problem there.

I checked the alternator harness connector voltage while the engine is running and got the following results with the alternator output at 12.20ish volts:

White/blue stripe .94v

White/red stripe 1.64v

Black/yellow stripe 0v

White/green stripe 0v

Other Info that may be helpful:

While I was replacing the clutch, there was a slight drizzle that got under the hood wet. I did have the battery disconnected during the entire job, but I wonder if when I turned the car on several hours later, even though everything looked dry, maybe there was an electrical spike in the alternator wire harness that may have shorted something out?

Also, if I turn the car on first time during the day, I will get 14.24ish volts from the alternator, but after the car warms up, the voltage unexpectedly drops to 12.20volts and then the battery light comes on. This seems to always happen.

Could the problem be with the ELD unit or a bad pin on the alternator output pin on the ECU, and if so, how would I test for these potentially problems?

Thanks in advance,

Ernesto

 

Other information might be helpful - what kind of car are we talking about?

 

Oops my bad. I have a 2005 Honda Accord 4 cylinder 2.4 5 speed manual.

 

Check under-dash Fuse No. 18 (15A). That fuse and the Blk/Yel (IG) wire supplies the ignition input that turns on the alternator/regulator assembly. If no power goes through the Blk/Yel wire to the alternator when the ignition switch is in the ON or START position, the alternator will not charge.

 

Update:

I replaced the ELD and also tried installing another used alternator but neither one of them fixed them problem; the charging light still comes on when the car warms up. I also checked the fuse that someone suggested and it tested good both while the engine was cold and warmed up as well. I also found out that power does go through the black/yellow wire only when the engine is cold, but once it warms up, the power drops to either 0v or 20-60 milli volts (0.02-0.06v).

I did a voltage drop test and got the following results:

Positive battery cable to positive alternator post
0.14v

Negative battery cable to alternator ground (body)
0.05v

These look like good results.

The problem is consistent. Whenever the car is cold, the alternator puts out 14v. Once the car warms up, it drops to 12 volts and it stays there as long as everything is warm. If I let it sit over night, it would put out 14v again when cold and then drop again to 12v once warmed up. Other than a bad ground wire which I may want to check one more time, I'm starting to think the problem may be a bad ECU. Any other thoughts?

 

There is an open (break) in the circuit. That would cause your issue.

 

Are you suggesting that there is an open circuit only when the car warms up but the circuit closes itself when the engine is cold?

 

Regardless of whether it is cold or warm, there should be power through the Blk/Yel wire to the alternator when the ignition switch is in the ON or START position. This indicates a break (open).

 

I replaced the alternator, the ELD, and I sent the PCM to a company to have it inspected, but nothing was wrong with it. The circuit that controls the alternator low/high output works.

At this point the problem is either a bad ground or a bad connection. I need to wait until I get my PCM back and I'll keep everyone posted. If anyone has any ideas feel free to share, I'd appreciate it.

 

This sounds very odd. I would suggest you check for continuity between PCM connector terminal C2 and alternator 4P connector terminal 2 (white/green) but you sent that out for inspection. If you had a wire grounding (a short) that shouldn't affect the altenator output at worst it would just kill the engine. Try the headlight test. Although normally I would test the regulator which seems like your culprit because you mentioned this happening after it warms up. If your ECU was bad you would have more problems than weird voltage issues. The ground for the ECU is usually found on the passenger side of the engine. Have you checked the battery with a hydrometer? Sounds like a bad cell. But that wouldn't explain the low output from the altenator. Easiest test for an open circut (or grounding wire) is to pull off the Positive battery cable and if it sparks when you put it back, you got something pulling power.