2001 jeep grand cherokee the compass/temp reads -40F the compass seems to be fine its just the temperature that is not working

ok no engine stated?
if gas engine, ?
I bet never tuned-up up in decade,right?> that gets 99% here.
but it can be far more complex, not guessing,,
what if , the ECT reads wrong.
and the PCM thinks you are in ALASKA,and you are in key west,FL..
so,it floods cranked. and cold running,same...

all EFI cars do that ,everyone, like that.'

forget heater (that blow'r motor sucks 15amps and alternator puts that load on the engine, breaking the CAMELS back, for get that
fix MISFIRE COLD that is the problem.!! real.

and new spark plugs top that list????
a rich engine needs more spark, and on HILLS

and scanning the ECT.
does ECT read correctly first thing in morning before starting engine
yes ECT can be scanned keyon, not started.

correct means if last night was 40f, the ECT is 50f in morning
or lower. say 41f.
-20f wrong, 0f wrong , got that? not blow average of last nights
ambient air temps or garage temps parked. there.
the air cleaner can be packed.up
the ISC valve stuck (my 4.0L did that ever 10k miles)most of the cured in 90s with better ISC
leaking injectr.
misfiring cold
and more
best is a tuneup ,pray, and work form there.
doing tests.

is this a compass car?
or are you say fiddling he electronic compass on a grand Cherokee.
or the compass on a compass, OMG.

if fiddling the electronic compass
the operators guide covers that.
lost that.
its here.
2004 and up

http://www.jeep.com/en/owners/manuals/


read the manual first, then ask for help of lost.

it is there, read it.

no symptoms posted, just and wide range easter egg hunt and no engine or transmission options stated "drive line" which.?

there are many temp sensors. on jeeps. and more each year it seems.

1. EFI ENGine temperatures. ECT.
2. transmission temperature (TCM input)
3. outdoor air temp. (and option mine has... case in point)
4. air temperature of the air inducted in to the engine (EFI IAT)
5. HVAC , climate control temp sensors. at least 2.

post symptoms, then ask how to diagnose car.

the sensor in front of the raid is bad

Normal reading is around 195 degrees F. Probably needs heater control valve or backflushing of heater core.

check your transmission level fluid and engine oil level. might be leaking and need some refill. make sure that your thermostat is working or maybe not, check your fan if it is spinning in the right time which your coolant temperature sender sense a very high temperature. or get the lowest temp sender sensor rating.

does the car start? if it doesnt...then your battery is dead. see if it"ll jump start at least for awhile, if it does and dies again...your alternator could be bad and not charging the battery.

Check the auxiliary cooling fan for operation. As the engine temp rises, it should kick on to bring the temp down. U may have a bad motor on the fan, or more likely a bad fan switch.

If you changed the coolant temperature sensor and it had a 5 volt ref signal to it then you replaced the wrong part. You need to replace the coolant temperature sending unit.  The coolant temp "sensor" is an input to the ECM for your fuel injection system. The coolant temp "sending unit" is for coolant temp reading at the gauge, It is an NTC switch (negative temperature coefficient) which means as temp increases/resistance decreases. 

All that info is actually relayed from the PCU which is expensive to replace.
Have a certified dealer look at it before you go replacing parts.