I have a 2001 Dodge 3/4 ton 24v truck. It has a little over 149k miles on it.

Here's the issue:
I started the truck this morning and it didn't want to start all the way. So I let it sit for a minute then it fired right up. Dropped my daughter off at school and headed off to work. Got about a mile from home and the check gauges light came on and the battery gauge was pegged all the way over to 18 with the dash lights flickering some. Pulled over as soon as possible & checked the codes by turning the key. Pulled code P1594. Turned around came home, checked it w/ my OBD2 reader and it didn't pull any codes. I can't seem to find the code anywhere. Talked to another friend and he seems to think that regulator went out.

Any ideas. Usually hubby would check it, but he's at a field exercise training right now with no cell phone service.

 

P1594 is charging system to high...battery voltage sense input above target charging voltage during engine operation


no big surprise there eh


I aint much on electrical but I do know that there is a heat sensor under yer drivers side battery that regulate voltage charge .....its basicaslly a cascade system reading the battery temp and adjusting voltage input..........for whatever thats worth

 

Yeah that's a "Voltage too high" code basically. I'd say it's an alternator. Did you get a red "Battery" light or something similar on while the engine was running? That typically means the voltage regulator has shorted itself to ground.

With the engine running drop a volt meter across the battery terminals. If you get substantially more than 14 volts you're over charging.

 

Next question. Is there an easy fix, or does it look like the truck may be down for a while. I drive approx 40 miles to work round trip each day so this really is not a good thing to have happen right now.

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I got a red Check Gauges light, that's what got me to look at everything. Why do these things happen when hubby (who is a diesel mechanic) is gone for 2 weeks.

 

Here's what all data says to do:


SYMPTOM
P1594-CHARGING SYSTEM VOLTAGE TOO HIGH

WHEN MONITORED
With the ignition key ON and the engine speed greater than 0 RPM .

SET CONDITION
When the PCM regulates the generator field and there are no detected field problems, but the voltage output does not decrease.

POSSIBLE CAUSES

* Target voltage differs from battery voltage
* Intermittent condition
* Ambient/batt temperature sensor
* Generator field coil short to ground
* Generator field short to ground
* Powertrain control module

 

 

The Battery Temperature Sensor (BTS) is attached to the battery tray located under the battery.

The BTS is used to determine the battery temperature and control battery charging rate. This temperature data, along with data from monitored line voltage, is used by the PCM to vary the battery charging rate. System voltage will be higher at colder temperatures and is gradually reduced at warmer temperatures.

The PCM sends 5 volts to the sensor and is grounded through the sensor return line. As temperature increases, resistance in the sensor decreases and the detection voltage at the PCM increases.

The BTS is also used for OBD II diagnostics. Certain faults and OBD II monitors are either enabled or disabled, depending upon BTS input (for example, disable purge and enable Leak Detection Pump (LDP) and O(2) sensor heater tests). Most OBD II monitors are disabled below 20 °F

 

Basically what all that is saying is that you could have a PCM keeping the charge signal on, you could have a failing alternator or the battery temp sensor could be causing the problem. You should be able to test out the battery temp sensor with what I gave you above. From what I gather if the resistance across the battery temp sensor connector is high (i.e. reading cold temps) then it will keep the charge signal on (via PCM signal) to the generator/alternator. I'd like someone else to varify this last bit though.

It might be hard to test out the generator/alternator connector without the scan tool because enables you to turn the signal on and off. The purpose of the test is to see if you have a stuck PCM driver keeping the generator/alternator charge signal on even when it's supposed to be off by command.

 

That's not what I wanted to hear. Luckily there is a parts store right outside base where the owner has a cummins. I think I'll head over there in a bit to see if he's got a way to help me out.

thanks

 

All you do is head to the local parts store and tell them your light came on and have them check the alternator. Most any of them do it now for free and you won't have to touch a thing.

If I took the truck in they would tell me to pull the alternator and bring it in so they could test it. If I send the wife over with the truck, she doesn't have to do anything. They pull it, test it and re-install it or the new one and send her on her way.