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Alternator Voltage with Failed Intake Temperature Sensor

Bzzzt

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Joined
Jun 17, 2020
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I thought I'd throw this out there since if it happened to us it will probably happen to someone else.

We noticed a low charge rate of 20 amps to the 240Ah LiFePO4 house batteries in our Ram Promaster (100A is more typical). This coincided with a check engine light. A multimeter showed around 13.6 Volts at the alternator rather than the usual 14.7. I figured we had finally blown up the alternator with our high current draws.

However, a code reader showed that the air intake temperature sensor had failed. This turned out to be a bad connection rather than a bad sensor (it's just a ntc thermistor, pretty hard to break).

It appears that when the sensor fails the van looks around for any other temperature information it has and/or picks a safe guess. Apparently it decided that the temperature was very high and lowered the alternator voltage in order to keep a safe voltage on the van AGM battery.

A sliver of a guitar picked fixed the connector and the new alternator gets shipped back to Rockauto.

Hopefully this can save someone out there some hassle!
 
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