Volt meter snaps to -8

[tuffs93]

Hi, I don't chime in very often but I'm at my wits end and maybe some one else has run across this problem. When driving my 04 2500, the volt meter snaps to zero ( -8 ). The truck continues to run but slowly drains the battery. Have replaced the alt. and the integrated power module and still have the same problem . The dealership mechanics that I know are stumped as well. The batteries load check good and all of the connections are clean. Here in Az. we don't have as much corrosion problems as wet areas do. One other thing, you can let it cool off and restart, the alt. charges and keeps the batteries going for about 2 miles then something snaps under the hood and here we go again, almost like a relay. Any help would be appreciated . Thanks, Mike

 

[Bob4x4]

It is ECM controlled, there should be some Dtc to give you a starting point

 

[tuffs93]

Bob,
Shouldn't there be a ck.engine light on ? Going to go after work tonight to see if there is any dtc codes.
Mike

 

[tuffs93]

Bob,
Got three codes ; p0622 Generator field not switching P2503 Charging system output low P2502 Charging system error. Could these have occurred before changing the TIPM and the alt. ? Could it be the ecm causing the volt meter to peg ?
Thanks, Mike

 

[JHumphries]

What happens if the temperature sensor fails and the ECM thinks the battery is extremely hot?

 

[sag2]

Check the engine ground first near the fuel filter. If OK, here is the diagnostic.

Symptom:
P0622-GENERATOR FIELD NOT SWITCHING PROPERLY
When Monitored and Set Condition:
P0622-GENERATOR FIELD NOT SWITCHING PROPERLY
When Monitored: When the ignition is on.
Set Condition: The feedback signal does not match the commanded signal for the voltage
regulator.
POSSIBLE CAUSES
GENERATOR
OPEN DRIVER CIRCUIT
GEN SOURCE SHORTED TO BATTERY NEGATIVE
(K20) FIELD DRIVER CIRCUIT SHORTED TO VOLTAGE
GEN SOURCE OPEN
ECM
TEST ACTION APPLICABILITY
1 Turn the ignition off.
Disconnect the Generator field harness connector.
Check connectors - Clean/repair as necessary.
Measure the resistance between the generator field terminals.
Is the resistance between .5 and 15 Ohms?
All
Yes → Go To 2
No → Replace the Generator.
2 Disconnect the ECM harness connectors.
Check connectors - Clean/repair as necessary.
Measure the resistance of the generator driver wire between the generator harness
connector and the ECM harness connector.
Is the resistance less than 10 ohms.
All
Yes → Go To 3
No → Repair the open driver circuit.
3 Measure the resistance of the generator source circuit between the generator harness
connector and battery negative.
Is the resistance less than 10 ohms.
All
Yes → Repair the Gen source shorted to Battery negative.
No → Go To 4
190
DRIVEABILITY - DIESEL
TEST ACTION APPLICABILITY
4 Measure the voltage between the (K20) generator field driver circuit in the generator
harness connector and battery negative.
Is the voltage greater than 1 volt?
All
Yes → Repair the (K20) Generator field driver circuit shorted to voltage.
No → Go To 5
5 Measure voltage of the Gen source circuit at the generator harness connector.
Is voltage within one volt of battery voltage?
All
Yes → Replace the ECM.
No → Repair the open or high resistance of Gen source circuit.
191
DR

 

[tuffs93]

Thanks Guys, the next day off is Thrus. so will be digging into this, Hopefully it will be something simple,will let you know
Mike

 

[PWong]

What happens if the temperature sensor fails and the ECM thinks the battery is extremely hot?

I think ECM would stop charging the passenger side battery and give you a DTC.
The two batteries would be driven to dead finally.

 

[JHumphries]

I think ECM would stop charging the passenger side battery and give you a DTC.
The two batteries would be driven to dead finally.

You can't charge or not charge one battery, they're connected in parallel. I was curious if the computer would stop all charging if it thought the batteries were too hot, or cold for that matter. I'd like to see what happens when you charge a frozen battery, from behind a blast wall of course!

 

[PWong]

You can't charge or not charge one battery, they're connected in parallel. I was curious if the computer would stop all charging if it thought the batteries were too hot, or cold for that matter. I'd like to see what happens when you charge a frozen battery, from behind a blast wall of course!

Yes the passenger side battery can be overcharged until it explodes and at the same time the driver side battery is not getting any charge and runs to dead.
This would happen when the crossover cable is defective and the connection between the two battery positive posts is BAD.
The temp sensor was underneath the driver side battery. The charging cable was hooked up to the passenger side battery positive post.
Depending on the temp sensor signal from the driver side battery, ECM would have a target charging voltage.

Never heard about a frozen battery but a lot of exploded batteries.

 

[tuffs93]

Hey guys, thanks for all the great comments and suggestions. Bob, went thru all the checks listed and no problems.... Took it out for a test run and it had a failure almost within a 1/2 mile. Got it back home and the new alt. I had just installed a couple weeks ago had failed, back to the dealership and naturally the had to order one. New alt installed and its been running since. My own screw up, I assumed the new alt was good. Thanks for all the comments. Mike

 

[sag2]

Thanks for posting the fix. It does seem a bit unusual that both alternators had the same failure mode. When that happens it is natural to start looking other places for the problem.

 

[rashwor]

Earlier this year my volt gauge dropped to 8 and the check engine light came on. Replaced alternator and all has been fine since. I agree it is pretty rare to get a new alternator bad out of the box.

 

[tuffs93]

The reason I said it was my screw up is because the first alt. was a reman. Usually I don't have problems with these but here lately it being more and more common. A friend of mine that owns his own shop and almost always uses reman stuff because of cost has been having a lot of trouble with them too. I've used them for years with no problem, but have learned my lesson this time. Thanks for all the great suggestions....