Please help me diagnose a problem with my daughter's 2003 Honda Accord LX, 4 cylinder, auto tranny.

About a month ago, the car would lose electrical power intermittently at idle. Tach would go to zero, speedo to zero and radio would go off. CEL would trigger.The car would not, however, stall and require a restart. She said that, under light trottle, pulling away from a stop, the car would "stumble", like it wanted to stall, but then would run OK. Car would run fine at speed.

She took the car to the local Honda dealer, where they pulled Code P0685, power failure, but could not replicate the problem. Tech cleared the code and sent her on her way.

The car would intermittently have the same problem. She was home this weekend and we took the car to the local Honda dealer. Same code - ECM/PCM internal circuit malfunction. Tech updated software, cleared the code and said if it happened again and the CEL triggered, we would need to replace the ECM - about $900 w/labor. I asked them to check relays/fuses and was told that all electrical connections were OK. The car ran fine over the weekend and she took it back to her home.

On her way to work today, same symptoms. Tonight, same symptoms, plus headlights went out. The car never stalled, however, and the CEL was not triggered.

The only previous electrical problem we have had with the car was a corroded positive battery terminal. Replaced with a "spiced in" connector and battery replaced. The deal with the headlights going out, but the car not cutting off, makes me think that the problem is electrical, rather than in the ECU.

Any advice or suggestions would be greatly appreciated. Thanks!

 

I would inspect that battery cable that was repaired. Try wiggling the positive cable when the car is running to see if it stalls the car.

 

If the positive cable was corroded, putting in a splice may not have been enough. When you check out the cable, try wiggling BOTH ENDS of ALL the battery cables. Pay special attention where the end-connectors are swaged onto the actual cable.

In fact, wiggle all parts of the cables. It's possible for the wire to be corroded inside its insulation so it looks good from the outside.

 

Thanks for the responses! I wish daughter was in town so I could try troubleshooting this myself, but we are at the mercy of a non-local dealer. Sounds like the battery cable might be the likely culprit. Better than a $900 ECU!

 

i have to agree with PA and JIM,, to make sure that cables are clean of corrosion and tight, you might have to install new cable ends if they are corroded

 

I have the exact same symptoms on my 05 Honda 4 cyl Automatic.
Right now I have a quote from my mechanic who is looking to update my ECU tomorrow. If this doesnt work I'll be staring at a new ECU purchase and install, which of course I'd like to avoid.
Any help is greatly appreciated.

 

Well, try the stuff we suggested. Unfortunately it's pretty common to never hear back whether our suggestions helped solve the problem.

 

Guys:

Thanks for the help last year. I apologize for not circling back and updating this post with a final report. I tried to send a PM to Art but I am not certain that it went through.

In any event, the problem did turn out to be the aftermarket battery terminal that my local dealer spliced in when the original terminal became corroded. The splice was installed rather poorly and the corrosion continued into the battery cable. This faulty connection caused a problem with the ECU (IIRC - in any event, the electronic part that was affected was located under the carpet in the front passenger foot well). I've asked my daughter to look at the repair invoice and get the part number for me and I'll post it when I receive that information.

In any event, the dealer in the town where my daughter lives finally diagnosed the problem correctly. They removed the aftermarket terminal splice hack job, installed an OE battery terminal wiring harness and replaced the ECU. The car has run flawlessly since the repair was completed. The total cost was around $900, as I recall. To their credit, my local dealer covered the cost of the diagnosis and ECU repair and reimbursed me for the cost of the original splice hack job that created the problem in the first place. I covered the cost of the proper repair to the battery terminal wiring harness.

Hope this update helps. I'll post the part number for the replaced parts when I get that info from my daughter.

 

Oh, so the flaky voltage actually damaged the ECU? I hear people saying all kinds of flaky things happen when the voltage goes low, but it all gets better when the battery/cable/whatever is replaced. I'll have to keep that in mind.

Thanks for the update.

 

I've got a copy of the repair invoice from my daughter and provide the following update. My recollection that the problem was in the ECU was not correct. The ECU was "updated", however.

When the tech checked the car again, after it had exhibited the same problems as before, it threw Code P0685 - ECU Power Relay Open. The tech found the positive battery cable to be corroded and cracked. Replaced cable - part no. 32111-RAA-A50 (Cost: $97.73).

The tech also found the ELD Electric Load Detector faulty. Replaced under the hood fuse box - Box Assembly part no. 38250-SDA-A01 (Cost: $428.70). Cleared the codes and test drove the car.

Total invoice: $1,027.72, which included rental car charges of $90.13.

These repairs were completed 11/5/09. The car has had no subsequent problems. Hope this update is helpful.