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JimCal · 06-27-2008, 11:21 AM

Just a few comments on a recent experience with my motorhome. After making a short test run in my MH in preparation for an upcoming trip, I returned home and parked the unit on the street in front of my home. A half-hour later I went to move the unit. When I moved the ignition switch to the RUN position, the only thing displayed on the instrument cluster was the odometer. There was static coming from the speaker of my rear-view-camera. Moving the ignition switch to the start position resulted in the instrument cluster displaying ALL lighted icons with all gauges at zero. No reaction from the starter.

My first thought was the battery - it was five years old - but it read 12.6 volts at the battery. I even disconnected the negative lead to do a 'cold start' on the computers. No help! Out of curiosity more than anything else, I started the genset and let it run for 10 minutes or so and shut it off. This time when I switched the ignition to RUN, all displays on the instrument cluster were normal and the unit started.

I moved the unit off the street, turned off the ignition, then turned it back on again to find that my problem had returned. Still suspecting battery, this time I left the ignition in the RUN position and measured the battery voltage again: 9 volts. What a shock!

With a new battery, I am back to normal. I have been diagnosing automotive problems for 50 years but this one through me for a while. I guess I know too much about 'old' technology and not enough about 'new' technology but I still persevered.

If this happens to you, give the truck battery a hard look before you call the tow truck.

Jimcal

JimCal · 06-27-2008, 11:21 AM

Just a few comments on a recent experience with my motorhome. After making a short test run in my MH in preparation for an upcoming trip, I returned home and parked the unit on the street in front of my home. A half-hour later I went to move the unit. When I moved the ignition switch to the RUN position, the only thing displayed on the instrument cluster was the odometer. There was static coming from the speaker of my rear-view-camera. Moving the ignition switch to the start position resulted in the instrument cluster displaying ALL lighted icons with all gauges at zero. No reaction from the starter.

My first thought was the battery - it was five years old - but it read 12.6 volts at the battery. I even disconnected the negative lead to do a 'cold start' on the computers. No help! Out of curiosity more than anything else, I started the genset and let it run for 10 minutes or so and shut it off. This time when I switched the ignition to RUN, all displays on the instrument cluster were normal and the unit started.

I moved the unit off the street, turned off the ignition, then turned it back on again to find that my problem had returned. Still suspecting battery, this time I left the ignition in the RUN position and measured the battery voltage again: 9 volts. What a shock!

With a new battery, I am back to normal. I have been diagnosing automotive problems for 50 years but this one through me for a while. I guess I know too much about 'old' technology and not enough about 'new' technology but I still persevered.

If this happens to you, give the truck battery a hard look before you call the tow truck.

Jimcal

Oemtech · 06-27-2008, 01:19 PM

Jim,
Welcome to IRV2.... May I suggest that you add some info about your rig (make, model etc) in your profile.

12.6 with no load has caught most of us at one time or another. I have a Briggs&Stratton starter sitting on the shelf to prove it.

Mr. Proto · 06-27-2008, 07:47 PM

That under load battery thing has caught more than one person you can be sure of that. It is that old saying in the business "It can't be my battery, my radio still works"

oldusedbear · 06-30-2008, 06:04 PM

Here is an insidious byproduct of the low battery situation. Let's say your alternator has failed but you don't know it. You're bopping down the road and haven't noticed the battery voltage is getting progressively lower - - engine seems to still be running OK. Now, you do ANYTHING that dramatically increases the load - - headlites, AC, cigarette lighter, SOMETHING that draws quite a few amps. Not only will the voltage drop to where the engine quits (you're in the fast lane of course), but IF YOU HAVE AUTOPARK, IT WILL APPLY. Even if you shut off whatever the big load was, the AutoPark pump will now try to run to release the brake, and IT is a large load by itself. Definitely NOT a good situation.

It PAYS to watch the instruments - - better yet, get something like a ScanGauge that gives you even more accurate readings of voltage, temps, etc.

max49 · 06-30-2008, 07:23 PM

OK, Everybody seems to have a 'scan gauge' except me. Where do you get them, how much and how/ where do you hook it up?
I never thought about, if the battery quits charging and gets low, the autopark applies.

texans · 07-01-2008, 02:56 AM

I know this is hindsight, but one thing that can be done in a situation like this is to hold down the battery crossover switch and bring the house batterys on line. Richard

Uncle Sam · 07-01-2008, 05:21 AM

What you were reading is the surface charge of the battery. After you put a load on the battery it showed a low battery at 9 volts. When ever I was testing a battery I would load the batterd down ;by either cranking the engine or turning the lights on for a while. It would then show the true voltage.

oldusedbear · 07-01-2008, 11:48 AM

Max - - Google ScanGauge II for complete info. About 170 bucks. Gives you lots of good information like voltage, temps, error codes, mph, rpm etc. Data is coming from the onboard computer. Selling like hotcakes now with all the folks wanting to monitor their gas mileage.