High volatgae, but not really.

2001 2500 4x4, 5.9, auto trans.

Got "check gauges" warning chime and indicator. Battery voltage pinned at ~ 18V, according to the instrument panel gauge.

I pulled over, shut the engine down and re-started. Everything good until I get home.

This sequence of events repeated itself for several days.

"OK" I sez to myself, " Should be nothing wrong with the alternator, must be the regulator circuit in the PCM". So, installed an external regulator. Same problem.

"So" I sez to myself, " I wonder if the instrument panel voltmeter is telling me the truth"?

I checked the voltage at the battery with the instrument panel gauge indicating ~ 18V. 14.8 V on my trusty Fluke 87.

No problem with the alternator or the new external regulator.

Ever since, when I take the truck out, it will give me the warning and high voltage on the gauge. I ignore it, and after several minutes, the voltage gets back to normal and the warning goes away. Sometimes it will stay this way until I get home, sometimes it will cycle several times until I get home.

What gives? Anyone ever have a similar problem?

The cluster gets its reading from the PCM, the PCM will send a high voltage signal across the CCD bus whenever the charging voltage reads above 16.7V. This will cause the gauge to peg at 18V and the chime to go off.

I'd start by verifying the accuracy of the internal voltage metering. Using your multimeter, probe from the alternator positive stud to either the alternator case, or battery negative. You'll need to be measuring while the cluster is expressing an issue. Either way, as long as all battery and charging connections are secure and free of corrosion, you're looking at a PCM issue either way. If it really is charging that high, bad PCM. If its reading incorrectly, bad PCM.

Though an external regulator may be working, the internal may still be bad. If internal is bad it'll tri the gauge whereas the external won't

dudeman2009 said:

The cluster gets its reading from the PCM, the PCM will send a high voltage signal across the CCD bus whenever the charging voltage reads above 16.7V. This will cause the gauge to peg at 18V and the chime to go off.

I'd start by verifying the accuracy of the internal voltage metering. Using your multimeter, probe from the alternator positive stud to either the alternator case, or battery negative. You'll need to be measuring while the cluster is expressing an issue. Either way, as long as all battery and charging connections are secure and free of corrosion, you're looking at a PCM issue either way. If it really is charging that high, bad PCM. If its reading incorrectly, bad PCM.

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I've done that, and the running voltage holds quite steady at about 14.8 when the dash gauge is pinned so I expect that you are correct and there is a problem in the PCM. I don't know how the voltage sensing circuit in the PCM actually works, but I expect that there would be a voltage divider of some sort to input the regulator circuit and output to the dash CCD bus. Probably not serviceable in any event. It is drive-able as it is and I don't think any harm is being done, other than the irritation of this intermittent chime and warning light.

E4ODnut said:

I've done that, and the running voltage holds quite steady at about 14.8 when the dash gauge is pinned so I expect that you are correct and there is a problem in the PCM. I don't know how the voltage sensing circuit in the PCM actually works, but I expect that there would be a voltage divider of some sort to input the regulator circuit and output to the dash CCD bus. Probably not serviceable in any event. It is drive-able as it is and I don't think any harm is being done, other than the irritation of this intermittent chime and warning light.

Click to expand...

It's probably just using a little ADC, and thats failed. That would also explain why the charging section of it hasnt failed, that would be using a DAC or mosfet to control the field excitation windings.

I'd be interested as to the final resolution to this. I had that happen to me sometime last year all of a sudden. Then as suddenly as it happened, it went back to normal... Didn't know what to think of it at the time. I checked an cleaned all on my grounding points since then and haven't had that happen since.