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Discussion Starter · #1 · (Edited)
Hi guys,
I need help diagnosing my 2001 Odyssey with 140k miles on it. Here are the symptoms: with all loads off (A/C, lights, hazards, etc) the van idles pretty normally and dash displays normally. With the A/C on things start getting weird. The tach and fuel gauge will occasionally drop to zero. The fuel gauge will also zero. Revving the engine to 1,500rpm will eleviate these symptoms.

I have an OBD scan tool so I spent the past half hour capturing some data. Here are my findings.

Leaving the accelerator alone and with no load, the voltage hovers around 13.5 volts; engine rpms are between 700 and 820. With the a/c on, voltage drops down to about 12 volts and rpm is within the same range. With full load (a/c, headlights, hvac on high, etc) the voltage drops as low as 10 volts, hovering between 10 and 11. The gauges appear to go on the fritz when voltage drops below 12 volts.

If I set the idle at 1,500 with the accelerator and return to the "full load" condition, the voltage registers between 13.5 and 14.4 volts. The gauges act normally.

With the engine off and keys out of the ignition, the battery shows 12.75 volts but the van seems to crank slower than usual. The temps are between 95 and 100F.

Is the problem with my alternator, my battery or some other subsystem?

thanks in advance,
Dave

BTW, there are no DTC error codes. The SRS light has been on since this started last weekend.
 

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2011 Odyssey LX, 120k miles
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It does not sound like there is a problem with the battery.

You might want to check the ignition switch. Search on that and you'll find an easy way to check it without removing too much other stuff (<20 minutes).
 

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If you are measuring the voltage on the battery terminals then your alternator is probably on the way out but couldn't hurt to have the battery tested. Flaky alternators have been known to give erratic dash lights on these vans.
 

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Discussion Starter · #4 ·
The 12.75 reading was taken across the battery terminals. The other erratic readings were taken from the OBD scan tool.

I'm leaning towards diagnosing it as the alternator. I wish I had the time to rebuild it myself. We've had this van for 8 years and this is the second (reman'd) one I'll have bought.
 

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Well I would agree with you that it sounds like it is the alternator, but before I would dig in and replace it I would pull the battery out and have it load tested for free at your local auto parts store. It would solve the headache of buy and replacing an alternator to find out later it really was the battery.

The SRS light will turn on when the battery voltage gets too low. You can follow the steps in this post below to clear the light.

http://www.odyclub.com/forums/24-1999-2004-odyssey/149996-srs-reset.html#post684406
 

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Testing the battery is a good thing but how/where were you getting below 12volts? You had 12.75 at the battery but the ODB tool was telling you under 12volts elsewhere?? If so maybe your ignition switch is on the way out like mentioned earlier. You may want to check the voltages coming into the fuse box especially from the ignition switch. If the switch has a voltage drop because of bad connections then most of the system will get the lower voltage. The switch is an easy enough swap and the part is under $100.
 

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Discussion Starter · #7 ·
The reading below 12 volts is coming from the OBD scan tool, that plugs into my OBDII port. The OBD scan tool is reading the vehicles voltage. I've forgotten my EE theory but the vehicle voltage should be the voltage from the alternator buffered somewhat by the battery.
 

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You need to check the battery voltage at the battery terminals after the engine has been off for couple of hrs, it should be more than 12.67volts. If it is below that level change the battery with a new one that has been fully charged. After doing this then go on to diagnosing other issues.
 

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You are reading too much in the problem. Checking the voltage with the scan tool can be way off. Always measure it at the battery. As mentioned above have the battery load tested if you do not know how to do it yourself. You would be best off taking it in and having the battery and alternator checked.
 

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If I set the idle at 1,500 with the accelerator and return to the "full load" condition, the voltage registers between 13.5 and 14.4 volts. The gauges act normally.
The scan tool may be off but he mentions the values above when running a higher rpm. At this point all is well. I assume that is also using the scan tool. More voltage checks are needed.
 

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AdvanceAuto can run a free diagnostic and let you know if it is the battery or alternator (or both),
 

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forgive if im wrong here, but the systems onboard are powered by the battery, not buffered by the alternator. all the alternator does is charge the battery. if i were a betting man, i would say your alternator is failing,, take it to auto zone or whoever and have it tested.
 
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