P1698 New alternator not charging

bigfish95971 said:

First somebody, maybe mopar1973man should be able to tell you how to test the pcm. There is also a cheap external voltage regulator you can install and have no negative repercussions, instead of replacing the whole PCM. Also check the two little wires on back of the alt. One should be from the pcm and the other should always be hot with the key on to energize the fields.

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Actually the only way to bench test a PCM is at a dealer with DRBIII tool.



Blue should have 12V with the key on. The green wire is a variable ground. All master grounds for the PCM, ECM and VP44 are on a single lead at the passenger side battery.



As for external regulators there is reason why those were ditched years ago. It's because it will cause shorten battery life because of improper charging voltages. External regulators only use the under hood temperatures for voltage regulation so on a cold day the voltage is super high and on a hot day the voltage is super low. It have zero regards for actual battery temperature so more time out of ten the batteries take on damage from under charging, overcharging or boiling out the water even on sealed batteries. The new PCM has a temp sensor under the driver side battery and monitors battery temperature as the battery charges so the battery temperature rises. So the regulator tappers back the voltage.

I only suggest the external regulator as a stop gap to allow the owner to continue driving the truck till he can get a replacement PCM. I do not suggest the external as a permanent fix because its not.

Let's say every vehicle I own I will get 10 years plus from batteries. My entire house is powered by batteries, solar and hydro generator too. So I understand how to properly maintain and service batteries for the long haul. This is only $4,800 to replace... I'm sure going to get 10-15 YEARS before replacement.

Mike, couple of questions. Are y9u saying here is no way to test the PCM regulating ground on the truck, rather than bench test? Don't the external regulators operate off of draw rather than temp?

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PCM can be tested by a DRBII tool at the dealer. That is the only thing I know that can test for proper operation of the PCM. There is no end user testing we can do really other than it charging or not.

No. External regulators work off of engine bay temperature. As the external regulator senses heat from the engine it tapers back the charging rate. Being there is only 2 wires to the regulator +12V (switch) on the blue wire which provides power to the regulator and the field of the alternator. The green wire is the field ground that is variable that the regulator produces. Regulator ground is the case itself. So there is absolutely no way for it to work from load. The only factor it has is temperature.

So an example. If you happen to have a bad thermostat and the truck never warmed up properly in the winter and the under hood temperature remained sub-zero your batteries would be boiling (gassing) as you drove down the road because the regulator would be over charging well after the batteries have warmed up and no longer required the high voltage.