Hey Guys, Hoping someone can shed some light on this problem. My 98 Durango 5.9 with the 136 amp alternator only shows 8 volts on start up. I had the alternator checked and it putting out 15 volts. The dashboard lights are dim, and the blower runs slow, but after driving a couple of blocks the gauge jumps to 14 volts and everything "perks" up. Do you think its possible the PCM is acting up in the cold?

Thanks

 

i would lean towards it being a bad battery before i would jump to the PCM, a weak (dying) battery will put a heavy load on the charging system, and immediately after startup the battery is considerably discharged

 

Yep, I agree on the battery being the issue.

 

Thanks, The batteries fairly new(2 Years) But it wouldnt be the first time a new battery crapped out on me.

 

Well its -19 C here this morning, and ended up driving the 10 km's to work on the battery, which got me here, but is now deader than a door nail. I had the battery tested on the weekend and it testted out ok ( 780 CCA @ 13V) . And since the alternator bench tested @ 15V, I am at a loss here. Any more ideas would be greatly appreciated.

 

If it went dead while driving then I would say your alternator is not charging. Even a bad battery would pick up some charge over a 10km drive.

 

True, but with the alternator putting out 15volts on the tester, and the voltage regulator being in the PCM, would it be safe to lean towards the PCM?

 

The voltage regulator is in the alternator.

 

You used to be able to buy just the regulator kits to install on the alternator, but the last time I tried they told me at the autoparts store that they couldn't get most of the kits anymore.

 

How are you checking the alternator for voltage output? DVOM? Here some information on the charging system.

CHARGING SYSTEM OPERATION

The charging system consists of:
•Generator
•Electronic Voltage Regulator (EVR) circuitry within the Powertrain Control Module (PCM)
•Ignition switch (Refer to Ignition System for information)
•Battery (Refer to Battery for information)
•Battery temperature sensor
•Generator Lamp (if equipped)
•Check Gauges Lamp (if equipped)
•Voltmeter (Refer to Instrument Panel and Gauges for information)
•Wiring harness and connections (Refer to Wiring for information)

The charging system is turned on and off with the ignition switch. When the ignition switch is turned to the ON position, battery voltage from the powertrain control module (PCM) is supplied to the generator rotor to produce a magnetic field. This is done through one of the two field terminals at the rear of generator.

The amount of DC current produced by the generator is controlled by the EVR (field control) circuitry contained within the PCM. This circuitry is connected in series with the second rotor field terminal and ground.

A battery temperature sensor, located in the battery tray housing, is used to sense battery temperature. This temperature data, along with data from monitored line voltage, is used by the PCM to vary the battery charging rate. This is done by cycling the ground path to control the strength of the rotor magnetic field. The PCM then compensates and regulates generator current output accordingly.

All vehicles are equipped with On-Board Diagnostics (OBD) All OBD-sensed systems, including EVR (field control) circuitry, are monitored by the PCM. Each monitored circuit is assigned a Diagnostic Trouble Code (DTC) The PCM will store a DTC in electronic memory for certain failures it detects. Refer to On-Board Diagnostics in Group 25, Emission Control System for more DTC information.

The Check Gauges Lamp (if equipped) monitors: charging system voltage, engine coolant temperature and engine oil pressure. If an extreme condition is indicated, the lamp will be illuminated. This is done as reminder to check the three gauges. The signal to activate the lamp is sent via the CCD bus circuits. The lamp is located on the instrument panel. Refer to Instrument Panel and Gauges for additional information.

BATTERY TEMPERATURE SENSOR

The battery temperature sensor 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.