Voltage Boosting Diode - JKU

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Originally Posted by turbomart

Fyi, ive fitted a resistor inline with my batt temp sensor which has boosted voltage to around 14v (ran about 13.6v previously).
Stock voltage is really to low if your running a calcium low or no maintenance batt. These batt have higher internal resistance and need higher charging voltage.

Does this mean that the PCM thinks the engine is still running cold and has disabled the O2 and other sensors?
Would this mean a change to fuel consumption as a result.. or maybe the lack of reporting problems to the OBD system as it still thinks it is in "warm up" mode?
Just some thoughts about that particular sensor.

[SeaComms]

I believe the battery temp sensor is only to do with battery charging as the engine will be a normal running temps long before the battery warms up to much. Charge levels will decrease when the battery is to hot.

As for the voltages, mine was charging the old stock battery at 14.6v when a cell collapsed. I wouldn't call that a low charging voltage?

This is from the allpar site:

The battery temperature sensor is actually inside the power module (or SMEC). It measures the air temperature as it flows through the power module, using the temperature to calculate the intake air density and target charging system voltage.

The battery temperature sensor reacts to different temperatures by producing a voltage between .04 volts and 4.96 volts DC, based on an input voltage of 5 volts DC. Because the logic module is so close to the battery, these readings can be used to estimate the temperature of the battery itself. Knowing the temperature of the battery is important because batteries are sensitive to heat, and the logic module will reduce the power sent to the battery by the alternator to prevent “cooking the battery.”

If the logic module detects a voltage outside the normal range (0.04 to 4.96 volts), it triggers a code 44 and the charging rate is set to 14.0 volts as a “safe” option. If the output of the sensor returns to the normal range, the logic module will return to normal operation and it will use the output from the sensor to adjust charging rates.

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The Battery Temp Sensor (BTS) is in fact located under the battery and determines the battery temp - I can't imagine any air flow over it given the shape of the battery tray or that it measures anything else.
The FSM for the TJ has an explanation as attached.

[turbomart]

Seacom, charge voltage is controlled by the pcm and is a complex thing, voltage will initially be high to boost batt after starting then drops down to a more sustainable level so as not to boil batt.
Cold batt temp gives a higher voltage, hot a lower one.
I have measured petrol zj, wj ,tj and jk and found them all to run below 14v whilst batt standing voltage measured 12.6 (correct value for charged batt).
If your getting 14.6v then thats good.

[Escapable]

Originally Posted by turbomart

Seacom, charge voltage is controlled by the pcm and is a complex thing, voltage will initially be high to boost batt after starting then drops down to a more sustainable level so as not to boil batt.
Cold batt temp gives a higher voltage, hot a lower one.
I have measured petrol zj, wj ,tj and jk and found them all to run below 14v whilst batt standing voltage measured 12.6 (correct value for charged batt).
If your getting 14.6v then thats good.

I think the point is missed in this one: The voltage was higher to reflect the additional charge required by the collapsed (damaged: non functional) cell.
When a battery is not charging or has a damaged capacity, it will require more current to put that charge back into place.
This has absolutely nothing to do with the temp of the battery, rather the determination of the PCM of the status of the batteries charge capacity (and this will be reflected in OBD codes when appropriate).