2002 Marquis chassis battery discharges

[Robert and Wanda Lindgren]

Every time I park the coach in storage I turn off the two main cut off switches in the battery bay. When I return 4-5 days later the chassis batteries have discharged and will not turn over the engine. The house batteries are just fine and with their help I can start the engine. I installed new chassis batteries and this did not solve the problem. Is there something else I need to turn off?

[Jim Murray]

2000 Marquis with the EXACT same problem, after new chasis batteries

[Gerald Farris]

I think that the problem that both of you are having is caused by the fact that the 12V positive wire to the ECM (engine control module) does not run through the cut off switch, but it runs directly from the positive battery cable on the starter to the ECM.

I think that the circuit to the ECM runs through a fuse box on the side wall of the battery compartment that is closest to the front of the coach. There is a fuse in that fuse box marked ECM, and removing it should stop your drain of slightly over 1 amp that is discharging your batteries.

Caterpillar designed the ECM to have power at all times to maintain the keep-alive memory and that is the reason that Beaver did not run it's power supply through the cut off switch. There is a possibility that cutting the power off to the ECM may cause problems, although I have not heard of any problems from owners cutting off power to the ECM. Most owners just remove the negative battery cable to the chassis batteries.

Gerald

[Keith Moffett]

I don't have the current name to hand. but I spoke with the Tech from the manufacturer of the solar panels on our '98.  He said that they charge the chassis batteries and if the connections are bad or the controler is shot or if they are just in the dark too long they will drain the batteries.
Was this changed on newer models?

Keith

[Gerald Farris]

Keith;
The solar panels on your coach should be wired to the house batteries and not the chassis batteries. As the house batteries are charged your Echo Charger will maintain the charge level in your chassis batteries with current from the house batteries.

As far as the solar panels discharging the batteries in the dark, there are diodes in the circuit between the panels and the batteries that prevent this.

Gerald

[Keith Oliver]

Robert and Jim:

Same problem, solved by putting a cutoff switch between the negative post and all wires that connect to it.  Now when leaving the coach for any extended time, the extra step is to have everything off as before, lock the lockers, close and lock the door (step retracted) then the last thing to do is open the cutoff switch.
I have also added a small smart charger to maintain the Chassis batteries, as the echo charger died and the Solar panels are only wired to the house batteries.  So if plugged in, the smart charger continues to maintain the Chassis batteries.  If no AC power is available, at least they won't be discharging.

[Edward Buker]

There can be a secondary reason for leaving the power on the ECM. That one amp of draw is equivalent to 12 watts and this energy is consumed producing heat. Many electronics in a hostile environment are left powered on at a low level to drive off condensation and reduce the thermal cycle affects by having some residual heating maintained by the circuitry. I do not know if that was Caterpillars intent and if the relaibility of the ECM is enhanced by this low level power being maintained. Most modern memory in these type applications gets "flashed" and maintains its state of programming without any power source. Obviously this has to be the case given vehicles have batteries go dead all the time. I will see what I can find out.....it may take awhile.

later Ed

[Jeremy Parrett]

 I would be very careful using the house batteries to start the engine. You will put a huge load on the alternator and probably cause it to fail,as mine did,when the fuse blew on my Echo charger and the start batteries went flat. Start the generator with the house batteries and charge them up.The echo charger will charge the start batteries.