My car recently developed an issue with my alternator not charging while the car is rolling. Sitting still, the alternator output is 13.5-14v; but while rolling down the road (coasting in neutral, in gear giving it gas, or whatever), the alternator will not engage. The system voltage will gradually drain until below 10v and things start getting wacky. I can pull over and completely stop, and the alternator will begin charging again. What’s going on?

My car car is a 2000 Civic with this ‘03 Accord engine swapped into it. I have had this setup for a couple of years, and this is the first time I’ve had this particular issue.

 

Here are my readings at ECU connector E:

In gear 20mph
Pin 10 - 10.97v
Pin 11 - 1.12 v
Pin 12 - 5v
Pin 24 - 0.31v

Stopped
Pin 10 - 12.82v
Pin 11 - 10.51v
Pin 12 - 0.65v
Pin 24 - 12.71v

 

I have checked continuity of the WHT/BLU, WHT/RED, and WHT/GRN (as per a guy who builds harnesses for these swaps mentioned that he has seen them break); and they were good.

On to the next test. I will look at my ELD data on a scan tool.

 

1. Check the under-dash fuse (No. 18 (7.5A) on 2003 Accord or No. 15 (7.5A) on 2000 Civic) that feeds the Blk/Yel wire that goes to the alternator. Make sure the fuse is firmly in the slot in the under-dash fuse box. Also check the Blk/Yel wire and connections.

The Blk/Yel wire is the ignition input that turns on the alternator/regulator assembly. If no power goes through the Blk/Yel wire to energize the voltage regulator when the ignition switch is in the ON or START position, the alternator will not charge.

2. Also check the connections on the Blk cable that goes from the alternator to the under-hood fuse box.

3. Honda's utilizes a dual mode charging system to increase fuel efficiency and reduce drag on the engine on start-up. The ECM/PCM determines charging based on info. from the ELD. During heavy load, the ECM/PCM can set charging voltage for high output (~14V - 15V). During light load and start-up, the ECM/PCM sets charging voltage for low output (~12 - 13V).

The ECM/PCM will not shut off the alternator. The no charging issue will generally not be due to the ECM/PCM or ELD.

 

thanks. As an update, as soon as I hit 10 mph, the alternator stops charging. Ease back to 9mph, it starts charging again.

 

It's your altonator brushes and slip ring "take altonator out removed brush holder from back of altonator and sand slip rings with 400 sandpaper by spinning to rotar and hiding sandpaper against the area were bushes contacted them sand the remaining brushes with 320 sandpaper wrapped around a 12 deepwell socket ect blow dust out and reasemble parts and try it