Hello Everyone,


Does anyone know if there is an issue with just unplugging the battery temp sensor?


1996 jeep grand cherokee limited
4l i6
2wd

 

The PCM uses battery temp to reduce the charging rate when the battery gets hot. The resistance gets less as the temp rises so at infinite ohms, it probably won't charge at all. Just my opinion however.

 

so if it was going bad it would cause the gen light to come on? I had both the battery and alternator tested both tested good then the alternator went down to less than 10 volts.

they replaced the alternator but the other day when i adjusted the belt and got ready to put on the fan shroud again so it could be moved and such i started the van. ran just fine but the gen light came on. per the dash gauge the alternator was still putting out plenty of volts.

think it might have actually been putting out close to 16 to begin with then after the gen light came on dropped to about 14-14.5.

of course this is all on visual display of the gauge. since i can't find any of my many multimeters to get a real test on it.

of course it might not be bad as the battery stand is mostly gone and proir it was just sitting on the frame of the vehicle.

the one on the jeep is working just fine as far as i know, i have no charging issue.

also happy to say the jeep starts reliably now, just got to find out the headlight issue with them coming on at night by themselves, probably the auto relay (i do hear clicking when i turn the key) but i can't seem to find it.

 

Actually the 'battery temp sensor' is called the 'ambient temp sensor' and it is very important. I couldn't get mine inspected the year before last, and I am sharing my tale here that I earned through hard work and much aggrevation.
This sensor must work correctly as the pcm uses it to run the obd2 monitors, such as catalyst, o2, etc. If the monitors are not run and are only incomplete on the scanner, you will fail inspection period.
I had disconnected mine and replaced with a 50k resistor, which made the pcm think the temperature was always about -20F outside, and charge the battery higher. However the monitors will not run if they sense the outside temp is below a certain level. So if you pull the codes you might see code or codes having to do not with charging system but with the emissions. A scan tool is invaluable here and they are cheap on ebay. or bring it to AZ have them also check the monitors status. With no sensor, I can almost guarantee your monitors statuses are 'not ready' or incomplete.
However, it never caused the Generator light to come on, well I have a battery voltage gauge, but the charging was actually higher than with the old sensor hooked up. Are you sure the light isnt the Check Engine light?
If the voltage is flopping around like you say I suspect either bad connections, ground or battery connections or ..a bad alternator right out of the box which happens all too often.

 

no its the gen light
the alternator was replaced about 2 years ago and just replaced again even though it and the battery tested good because it went low when reading.

no the volt meter does not really flop around. yes when it started it was close to 16 volts but after the gen light came on it dropped to roughly 14-14.5 which is still good for charging (my jeep and prior jeep was always right at the 14volt mark).

i looked up some of the symptoms of a bad battery temp sensor and some of the things match what the vehicle is doing such as

battery/gen light coming on
surging on the vehicles engine which i had before thought was the result of changing the air filter that was on the vehicle (big 12 inch aftermarket filter and pan) to the one that the vehicle should have like a 6 inch one with a hose to the front of the vehicle. but right now it will surge even with the air filter and dog house off.

i could have tested the vans battery temp sensor by taking the one from the jeep since they use the exact same part. in fact many of my parts between the van and jeep are compatible with each other.

 

Correct, except if the resistance goes to infinite, or open,
as the case would be with the sensor unplugged, it should charge at max, if it is as simple as that. If it were 0 ohms like a dead short, thats when it wouldn't charge at all. However I think the pcm knows both of those conditions and only recognizes a range.

 

You can also test it with a resistance/ temperature chart for the sensor and an ohm meter, much more accurate. Also need to know the outside air temp that the sensor is sensing. Hope that helps.