Check engine light after chassis battery change

[Mablunk]

Our chassis battery doesn’t charge with shore, 12v or generator. It died so we changed it out. Now the check engine light stays on when we start it. Is there a reset button when the battery is disconnected?
Also, when the chassis battery is dead, the fridge won’t work even with shore power.
2018 Thor Ace 30.4.
Anybody got any ideas?

[10scDust]

At least our refrigerator's control power is 12V, not there, no working fridge.

Is your stow switch in the on/run position? Put it there, keep it there!

Is the converter running? Have you looked at your BIRD for its working?

Just a couple ideas, more coming soon!

[16ACE27]

Originally Posted by Mablunk

Our chassis battery doesn’t charge with shore, 12v or generator. It died so we changed it out. Now the check engine light stays on when we start it. Is there a reset button when the battery is disconnected?
Also, when the chassis battery is dead, the fridge won’t work even with shore power.
2018 Thor Ace 30.4.
Anybody got any ideas?

I disagree with the premise of your supposition.

The chassis battery is the one under the hood that starts the engine.

The house batteries are the ones that run house loads when not plugged into SP or running the generator.

Do you have a propane/120 VAC fridge?
Or a residential (only 120 VAC) fridge with an inverter?

You seem to have a lot of stuff going on. What has happened since it all worked correctly?

Without good information we can't provide good solutions. The chassis battery has absolutely nothing to do with running either type of fridge.

Did you ever find your USE/STORE switch?

[Mablunk]

The fridge is a 120/12 volt. It has an inverter under it to change
The fridge worked fine until the chassis battery failed. Then the inverter would start beeping and only the fridge wouldn’t work. When we disconnected the chassis battery that runs the engine, the generator started on its own, yes, the fridge was on. Shore power off.
We have a switch right by the door that is red when the power is going to the coach. When it’s off nothing works. I’m assuming that is the use/store switch.

When we changed out the dead battery after that is when the check engine light came on and stays on when the engine is running. Is there a reset button when the chassis battery is changed out?

[Mablunk]

Thanks everyone for your help. I really appreciate it. There’s so many switches and fuses everywhere. Sure glad my home isn’t this complicated.

[Mablunk]

Also, our 120 won’t work off the 12 v batteries. No microwave or plugs for coffee pot work on just house batteries even when fully charged.

[EA37TS]

Originally Posted by Mablunk

Also, our 120 won’t work off the 12 v batteries. No microwave or plugs for coffee pot work on just house batteries even when fully charged.

If you don’t have an inverter they are functioning as designed. If you do have an inverter, turn it on.

[The Gritz Carlton]

If you don't have a scan tool, you can run it by any auto parts store and they will scan the codes for you and find out what the check engine light is all about. You can also disconnect the battery, wait 10-20 seconds and reconnect to see if it will not come back on.

[EA37TS]

Originally Posted by Mablunk

Also, our 120 won’t work off the 12 v batteries. No microwave or plugs for coffee pot work on just house batteries even when fully charged.

If you don’t have an inverter they are functioning as designed.

[Mablunk]

Ok. We will disconnect the battery and wait. If it stays on after reconnecting we’ll take it to have it scanned.

Another question. Should shore power recharge coach and chassis battery and run all 12v and 120 equipment?

Thanks again everyone. [emoji1774]*[emoji3601]

[Mablunk]

Oh and the inverter under the fridge is on.

[Bob Nodine]

Originally Posted by Mablunk

Ok. We will disconnect the battery and wait. If it stays on after reconnecting we’ll take it to have it scanned.

Another question. Should shore power recharge coach and chassis battery and run all 12v and 120 equipment?

Thanks again everyone. [emoji1774]*[emoji3601]

On many coaches the engine battery is not charged by shore power and is only charged if the engine is running. On the opposite side the house battery is usually charged by the alternator when the engine is running.

So: engine running - both house and chassis (engine battery) are charged.
engine off and shore power connected - only house battery charged
engine off, no shore power but generator running - house battery charged
engine off, generator off, no shore power, but solar - house battery charged
engine off, gen off, no shore, no solar - nothing charged

[Bob Nodine]

Originally Posted by Mablunk

Our chassis battery doesn’t charge with shore, 12v or generator. It died so we changed it out. Now the check engine light stays on when we start it. Is there a reset button when the battery is disconnected?
Also, when the chassis battery is dead, the fridge won’t work even with shore power.
2018 Thor Ace 30.4.
Anybody got any ideas?

Confusing statements. The inverter and house system should only be connected to the chassis (engine battery) if the engine is running or the emergency start switch is held down.

If your frig is not running when the engine is off and no shower power and you hear a beeping sound most likely the house battery voltage is to low for the inverter to work. Start the generator or connect to shore power and charge up the house battery. You should be reading above 13.5 volts and most likely above 14 volts to charge the house battery.

If your engine light is on after you replaced the chassis battery while the engine is running you may have a bad alternator or you did not connect one of the cables that goes to the battery. Another possibility is that while changing the battery you blew out a diode in the alternator. Have the alternator checked or use a voltmeter across the battery while the engine is running. You should see a voltage above 13 volts if the alternator is working.

[10scDust]

Originally Posted by Bob Nodine

On many coaches the engine battery is not charged by shore power and is only charged if the engine is running. On the opposite side the house battery is usually charged by the alternator when the engine is running.

So: engine running - both house and chassis (engine battery) are charged.
engine off and shore power connected - only house battery charged
engine off, no shore power but generator running - house battery charged
engine off, generator off, no shore power, but solar - house battery charged
engine off, gen off, no shore, no solar - nothing charged

I agree here, however, I have noticed on our RV; it stays sitting idle hooked to shore power in its home in an RV carport. Sometimes when I open a cab door (class C & the parking lights come on for their minute), I hear the BIRD make a knocking sound.
I believe it is doing its job by sensing full on one side switching to the other side to maintain full charges.
If I am correct, that is an exception to your stated rules, of which I agree to for the most part. The BIRD monitors between coach and chassis battery systems for charging not going to waste.

edit: Battery Isolation Relay Device

[Mablunk]

Bob Nodine
Thanks so much for that list. Perfect. We’re new to mh and we have few manuals so this is all pretty complicated for us. We really appreciate any help we can get.
One thing we did is check the alternator before replacing the old battery. We disconnected the neg cable while running and it continued to run. Is that test still accurate?
If so we will do that again when we disconnect to see if the check engine light goes out.
As far as our inverter, I think they put it under the fridge because there was room. When it’s beeping nothing 120 works.

[Beau388]

Originally Posted by Mablunk

Bob Nodine
Thanks so much for that list. Perfect. We’re new to mh and we have few manuals so this is all pretty complicated for us. We really appreciate any help we can get.
One thing we did is check the alternator before replacing the old battery. We disconnected the neg cable while running and it continued to run. Is that test still accurate?
If so we will do that again when we disconnect to see if the check engine light goes out.
As far as our inverter, I think they put it under the fridge because there was room. When it’s beeping nothing 120 works.

Modern vehicles have a solid state internal voltage regulator. This regulator uses the chassis battery as a sink to prevent voltage spikes when turning off and on electrical devices. Disconnecting either lead from the battery while the engine is running can result in a voltage spike (unregulated alternators can produce 120 volts easily) and easily damage connected equipment.

If your engine starts easily the chassis battery is good. If the generator starts easily (if shore power and the engine are off). The house battery(s) are good. You can use the inverter panel to check on the state of the house battery(s). The inverter always displays house battery voltage and can indicate whether the house battery(s) are being used or charged.
You can only check house battery condition when there is no shore power, generator off and engine off. If the battery's resting voltage shown on the inverter when the inverter is on is 12.7 or 12.8 volts the battery is fully charged. If the battery voltage is under 12.1 volts, the battery is fully discharged (less the 50% max charge). Next plug into shore power or start the generator. After a couple minuter the inverter voltage should read somewhere between 13.1 and 14.2 volts depending on the state of the house battery.

[Bob Nodine]

Originally Posted by 10scDust

I agree here, however, I have noticed on our RV; it stays sitting idle hooked to shore power in its home in an RV carport. Sometimes when I open a cab door (class C & the parking lights come on for their minute), I hear the BIRD make a knocking sound.
I believe it is doing its job by sensing full on one side switching to the other side to maintain full charges.
If I am correct, that is an exception to your stated rules, of which I agree to for the most part. The BIRD monitors between coach and chassis battery systems for charging not going to waste.

edit: Battery Isolation Relay Device

Sounds like you have a BIRD so the chassis battery would be charged from shore power.

BIRD = Bidirectional Isolate Relay Delay

many Class-C motorhomes have an IRD = Isolate Relay Delay and the chassis battery is only charged if the engine is running.

[Mablunk]

Originally Posted by Bob Nodine

Sounds like you have a BIRD so the chassis battery would be charged from shore power.

BIRD = Bidirectional Isolate Relay Delay

many Class-C motorhomes have an IRD = Isolate Relay Delay and the chassis battery is only charged if the engine is running.

Shore power doesn’t charge the chassis battery.
Ours is a class A not c.
When we’re on Sp shouldn’t that alone run the refrigerator?
Another question. There is a sine wave inverter under the fridge. I assumed that was only for when there is no Sp.
Is there another inverter someplace else?
We got the last class a on the lot. So, we have very few manuals.Therefore very little written info. Except of course we were left with 3 Tv manuals, lol.

[16ACE27]

Originally Posted by Mablunk

Shore power doesn’t charge the chassis battery.
Ours is a class A not c.
When we’re on Sp shouldn’t that alone run the refrigerator?
Another question. There is a sine wave inverter under the fridge. I assumed that was only for when there is no Sp.
Is there another inverter someplace else?
We got the last class a on the lot. So, we have very few manuals.Therefore very little written info. Except of course we were left with 3 Tv manuals, lol.

All manuals for your RV are available on the Thor Owners Resource Website.

It sounds like you never got a thorough walk-through/instruction on your coach when it was delivered. Did you buy it new or used? How long have you owned it?

It may well be worth your money to hire a mobile RV tech to come help you sort out your apparent problems and teach you about the systems in your RV. You are really not providing enough accurate information here for anyone to really help you. I.E., I doubt your fridge is a 120/12 volt fridge. It is either a 120 VAC fridge (most likely since you have an inverter); or a 120 VAC/Propane fridge. Also not sure you know the difference between an inverter and a converter.

[Bill Johnson]

Originally Posted by Mablunk

Ok. We will disconnect the battery and wait. If it stays on after reconnecting we’ll take it to have it scanned.

Another question. Should shore power recharge coach and chassis battery and run all 12v and 120 equipment?

Thanks again everyone. [emoji1774]*[emoji3601]

Now he decides to "test" your alternator by disconnecting the battery. After all, the car's ignition should be able to run on just the alternator's power alone.

Wrong!

The moment he disconnects either lead from your battery, it's entirely possible he caused thousands of dollars in damage. Here's why...

Your battery does more than just provide electricity. It also shorts AC, spikes and transients to ground. Removing the battery from the circuit allows those spikes and transients to travel around, endangering every semiconductor circuit in your car. The ECU, the speed sensitive steering, the memory seat adjustments, the cruise control, and even the car's stereo.

Even if your computers and stereo remain intact, in a great many cases removing the battery burns out the diodes in the alternator, necessitating a new alternator. I found this on many battery maker sites. I really hope nothing went wrong when the battery was disconnected.