ENGINE OVERHEATING DUE TO AC

SOURCE: engine code 95 jeep grand cherokee lerado

12 is a battery disconnect within the last 50 start cycles and 55 means the end of the diagnostic cycle.  Basically the computer found nothing wrong. The 12 code may seem incorrect if you haven't disconnected the battery recently, but from my experience the 12 code shows up almost all the time regardless.

SOURCE: 1997 Jeep Grand Cherokee Orvis with overheating problem

There may be coolant in the reservior but it doesn't necessarily mean there's any or enough in the main cooling system. If the radiator has a pressure cap, try replacing it with a known good one. Check and replace any coolant hoses that are kinked, or collapsed. There may be an airlock in the system - bleed it in accordance with the manufacturers instructions. Try flushing out the radiator and cooling system and then refill with the appropriate antifreeze / water mix ensuring that no air locks remain.

SOURCE: 1999 jeep grand cherokee laredo 4.0 litre

OK here we go you will need a test light for the following tests, i will try to be as descriptive as possible so lets get started

fist start the engine and turn on the a/c that should command the fan on.
right front engine compartment next to the battery is the power distribution center pop off the top, ground your test light to the negative battery terminal and find fuse number 10 it is a 40 amp fuse check both sides of this fuse with your test light, if you have power on both sides of the fuse than we shall go further.

unplug the connector from the cooling fan, there should be two wires in the plug one is dark green and the other is black with a pink tracer, with your test lite grounded to the negative battery terminal check the dark green wire for power, if there is power there than move your test light ground clamp to the battery positive terminal and test the black wire for ground,
if testing the black wire made the test light shine than the ground circuit is good, if it did not than check you ground connection behind the right headlight.
when testing the dark green wire, if the dark green wire made the test light shine and the ground circuit is good than you simply have a bad coolant fan motor.

I suspect you were not getting power to the fan motor so you will need to take a look at the radiator fan relay, this is a special solid state relay mounted to the inside of radiator core support on the right side down behind the bumper.

here you will find a single plug with 4 wires in it

black = ground
dark blue / pink = relay controll from pcm
dark green = output to radiator cooling fan
gray = battery power from fuse # 10 in pdc

unplug the relay ground your test light to the battery negative terminal, with the engine running and a/c turned on check the gray wire the test light, it should turn on if not recheck fuses.

move your test light to the battery posistive terminal and test the dark blue / pink wire, if the test light turns on than you have a bad radiator fan relay, you can pick one up at your local parts store for about $85.00 just make sure you get a high quality one the cheap ones have a hard time with the amprege consumption of that fan.

good luck

wesley [email protected]

SOURCE: my jeep grand cherokee started overheating at idle

try the water pump - first - make sure the radiator is really full - take the cap off cold and fill - if it looks full - start and run 8 minutes or so - then fill it up - look at ur fan belt - is it tight - tight is about how much pressure u use to make a firm hand shake with little movement - any movement over about an inch is loose - when the jeep warms up the belt can slip and not even make a noise - - new materials don't always squeal. - then be sure ur water pump is ok - they go slowing - the fins wear down - one more thing is the radiator - u don't say how many miles or what maintenance schedules you have or not so that's it for now

SOURCE: I have a 2002 Jeep Grand Cherokee Laredo with the

If you put the thermostat in correctly (spring towards the engine) that should be OK. Likely if the water pump wasn't leaking or had a bad bearing, you wasted your $ on that.
If you re-filled it and did not have the heater on high heat, you may have some trapped air in there. But, still overheating says another thing. If you have a blown head gasket, it can pump compression into the cooling system and drive the coolant from the core. It will also overheat. You can have that tested at most any decent shop that will do a hydrocarbon test to find that.I think someone makes a chemical test kit for that but not sure if it's very expensive or not. White smoke from tailpipe will also be an indicator as will be any coolant in the engine oil or coolant on one or more spark plugs. If it turns out that it has a head gasket problem don't stop looking for problems as often a faulty fan or obstructed radiator can cause the initial overheat that caused the gasket to fail.

Testimonial: "Thank you. I was hoping not to hear head gasket, but that's where it seems to be leaning towards."