I recently purchased a low mileage 2003 Accord LX 2.4L with 120k miles. Car is in nice shape but having electrical issues that I cannot find answer, I did the alternator test with multimeter and ground tests at alternator, body and enging and all were good.

Here are the symptoms:

When I bought the car, the starter was cranking slow. I checked the battery after the car had run a few minutes and the voltage was 15.2 volts (high). I left the headlights on for an hour an the voltage was 13.2v, I started the car and the alternator kicked in and measured 14.2v at the battery. Ran checks with multimeter running to check ground to body, ground to engine and ground to alternator, All ground readings below .03v, When I shut the car off, I checked the battery voltage and it was fluctuating from 14v all the way up to 15.6v. After sitting for 30 minutes, the battery voltage was still moving all over the place. Thought I might have a short in the battery and picked up a new battery upgrade Group 35 from 51R in the car. Car cranked a little better but was still slower than it should be, Battery was at 11,92v went I put it in. Went out and checked voltages and with alternator charging it was 14.2v at the battery, rechecked grounds for leakage and all readings were good. Checked ground straps and they were good shape and replaced battery ground with upgrade, after running the car for a few minutes, the new battery is now doing the same thing as the old battery, The voltages are going up and down and cannot get a steady reading, I only had the car running about 2 minutes and battery is going from 13.2v to 15.1v and keeps moving around. I cannot get a steady reading,

I disconnected the battery terminals and checked the readings on battery after setting for 20 minutes the battery is 11.98v so it was charging for those 2 minutes the car was running, I then checked the old battery and it was reading 12.1v after sitting for an hour, I put the terminals back on and the battery voltage started to rise and fluctuates with the ignition off. The battery voltage went up to 14.52v with the car off and sitting and then dropped to 14v and started rising again to 14.4v.

Would a bad starter with a short cause this? The starter is cranking slow and I do not have an amp meter to check how many amps it is pulling, I replaced the 51r battery with a 700CCA Group 35 so the starter should not be dragging or cranking slow, I have been working on my own car for over 40 years and never encountered anything like this, This is the first Honda I have owned--might be my last,

I have an XTool D7 Bi-directional Diagnostic tablet and the only codes I get are under ABS system. I got two 13 codes under ABS for left front wheel sensor. Live data from scanner shows 12.1volts and no other fault codes.

 

Your voltage readings are strange. IMO, I don't think a short would cause the readings you are getting. Just to be thorough, maybe try your volt meter on a different car to make sure it is functioning properly.

I'd suggest doing some more voltage drop tests. I think those were voltage drop tests where you got <0.03V. With the engine running, measure the voltage from the + alternator post to battery + post. Also + battery post to the + post on the engine bay fuse box. Also try on the - battery post to fuse box and also - battery post to the bolt on the subframe. This will help verify the large wires starting at the battery can carry enough current.

 

When I was getting the crazy readings on the Honda, I tested my multimeter on my Toyota to ensure it was working. I didn't do the + test to the alternator and fuse box. I will give that a try. What should the max readings be on + alternator and fuse box test? I

was thinking the voltage fluctuation would be caused by the ground but I also checked the resistance between body, engine, transmission and alternator everything was good. I was thinking of taking the battery back out and running resistance test between all the main positive and negative connections. Another think I did not mention is there is no spark when I hook up the battery and I would think there would be a little spark if there was a short somewhere in the system. When I pull live data, all the voltage readings look to be in spec for all the components. Also, when the battery was showing fluctuating readings, the reading at the OBD port was constant 12.1v.

I checked the grounding strap near the ABS and the one from body to transmission and they are in good condition. All the electrical components seem to be working except the radio has not sound and the dash has a few lights ABS, SRS, Warning Triangle and TCS do not illuminate when the key is turned on. The maintenance light is on.

I was trying to avoid having to change out the starter until I checked everything else but at this point I am considering replacing both the alternator and starter. The starter is quite a job on the 2.4L. I have never seen a car with voltage fluctuations when the key if off. I have never had any kind of electrical issues with my Toyotas and the starter and alternators always lasted over 200k,

 

You have to be careful with the resistance reading from a volt meter. The volt meter puts a very low current through the wire you are testing. If one of your large battery cable wires had a crack in the insulation and corroded down with only a few good copper strands in the center, your volt meter would still show low resistance. That large diameter corroded wire would not be able to carry the amps necessary, yet pass the resistance test. The resistance test with a corroded large cable would be the same ~ zero resistance as you would measure on a thin wire. That is why testing the wires with a load on the wires is more useful. I'd say the resistance check is only definitive if you get an open circuit on any wire as the wire is completely broken. ~Zero resistance on a wire has no meaning. Hope this makes sense.

With the engine running, I'd say a voltage of <0.5V across a wire is good. You should get an idea of a known good because some of your large wires should not be corroded. The lowest value you get would be ideal. Hopefully one voltage drop tests sticks out as the culprit. Just based on the issues you are having with voltage, I'd suspect you have a connection issue with the connector at the + battery post as that feeds the alternator and starter. Those voltage drop tests will give you a better picture.

I replaced the starter on my TSX 2.4L engine that is essentially the same as your 2.4L Accord engine. I only had to remove the upper portion of the intake manifold to get enough access to change out the starter. I think is 5-6 bolts on top and I reused the metal gasket. It wasn't too bad of job vs removing the entire intake manifold.

 

I checked the positive on the alternator. Stopping for tonight. I understand the positive battery cable runs to the alternator. Where is the source located for the starter cable. I could not find any information on checking the starter cable. On another forum on alternators and starters, the mechanic said to check the cable to alternator and cable to starter and also check for excess ripple. Going to do ripple test tomorrow but I cannot see behind the intake where the starter cable runs.

Thanks for the info on replacing starter. This car is in really nice shape for a 2003. Engine bay is clean and no oil anywhere. Paint is in good condition and interior is clean. I picked this car up thousands below the market value so I am willing to put some money into it. This if my first Honda and 2003 was supposed to be one of the best years.

 

The starter gets the main power on a large cable directly from the + battery post without fuses etc. The + battery post cables will end up in 3 places. The engine bay fuse box, the alternator, and the starter.

I don't know the exact routing of the + cable to the starter off hand, but you can put one lead of the volt meter on the battery + lead post and the other volt meter lead on the large post on the starter. Then you will have the voltage drop reading on that wire when you attempt to start the car.

 

I checked for voltage leak with engine running and the + side all connections are good. The cable is in good shape. I could not reach the + connection to the starter. I decided to test multiple grounds with the key off since that is when the voltage is fluctuating. All the ground straps good and I got the same reading. When I checked the alternator ground--red on battery plus and black on alternator bracket--the multimeter goes crazy. The voltage reading bounces up all around from 3v to 11v. That would explain the fluctuations at the battery. If I remove the + cable from batter and check the battery, the voltage stabilizes,

I will also mention that I went out and bought a new multimeter just to double check everything with two multimeters, My old Craftsman multimeter is over 20 years old so I went out and picked up a new one.

 

That test from battery + to the alternator bracket should give you ~12.6V. You can try repeating and unplug the multi-pin connector with the smaller wires from the alternator just to be sure there isn't an issue on the alternator control wires.

I'd say the most likely fix is replacing the alternator. I'm not a fan of remanufactured alternators from the parts stores. I typically get a Denso-brand alternator or find a place that rebuilds alternators if you have any in your area.

 

Thanks for all the help. I did pull the multi-pin connector and the voltage continued to jump all over the place. All the other checks with + on battery and checking ground gave solid 12.2v. The bracket on the alternator gives the wild fluctuations. I once bought one of those local box store remanufactured alternators that had a short in the alternator and caused the starter to drag. I agree with you on alternators but I was looking at an DESNO OEM remanufactured. The DENSO site shows you are basically getting new components in an old case. The other choice was a new REMY that have good reviews.

 

I used the Denso remanufactured alternators and starters on my Hondas with no issues. I haven't run into a quality problem with them so far.