"Gen" light comes on intermittantly

[Kramer]

Hi all,

96 XJ with the Gen light coming on for a minute or two when first started up - have checked the following:

1. battery is fully charged and less than 1 year old
2. alternator is clean (pulled it apart, cleaned, dried and re-assembled)
3. all connections good and tight and clean.
4. no draining (shorts) detected between neg cable and neg battery post


Everything works well and the rig is normal, including volts check.

Only mods electrically is a 16" thermal, run off a relay.

I can make the light go away if I load up the alternator - e.g., hi beam or air con - then the Gen light disappears instantly.

I laso have a code 44 - battery temp sensor - (BTW where is this sensor? Is it a "current" (amps) model of a thermal situation - i.e. it "thinks" that the battery is hot by the amount of charge current going to it?) .

THEORY - do I have a broken regulator that is overcharging the battery slightly? This would explain the going away of the Gen light when the charge is diverted to other load (e.g. Air con). How can I test the reg on a 96 model - the screwdriver slot test point that the earlier ones have is not on my model.

Long winded, sorry about that. Any advice would be appreciated!

TIA, Kramer

[Dave'n'Wen]

Mate I got this info from the FSM Hope it helps.

BATTERY TEMPERATURE SENSOR DESCRIPTION

The Battery Temperature Sensor (BTS) is attached to the battery tray located under the battery.

OPERATION
The BTS 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.

The PCM sends 5 volts to the sensor and is grounded through the sensor return line. As temperature increases, resistance in the sensor decreases
and the detection voltage at the PCM increases. The BTS is also used for OBD II diagnostics. Certain faults and OBD II monitors are either enabled
or disabled, depending upon BTS input (for example, disable purge and enable Leak Detection Pump (LDP) and O2 sensor heater tests). Most OBD II monitors are disabled below 20°F.

[Kramer]

Thanks for that info Dave.

Does anyone know if the the BTS causes the Gen light to come on? Does the ECU make an automatic correlation between the two?

Hmm the car works really well - there is no manifestation of any problems at all. Everything is great - maybe I should just take that little light bulb out of the dash?!?

Kramer

[Grant]

Do a simple voltage output test with a multi meter when gen light is on see what is actually coming out of alternator al low revs
once you take load off the alternator does the light re appear when vehicle is at operating temp?

[Kramer]

Volts pretty constant, even with air on and hi beam it only drops 0.5 V.


I'm going to check this battery switch out tonite.

[Kramer]

OK removed the BTS, checked in water. Changes resistance with temp - started at about 8 k-ohms and worked it's way down to 2 k-ohms at 70 deg C.

Put it back but left it unplugged, started, LIGHT ON. Plugged it in to the wire loom, LIGHT OFF. Disconnect - LIGHT ON. It did this consistently.

So today that light hasn't come on at all and I think ity's not somethiong serious so I'll leave it at that.

Thanbks for the input fellas. Would hate to have had to replace that alternater ...

[Dave'n'Wen]

No worries mate, good result.