Heater does not produce heat - 1998 Jeep Grand Cherokee

Depending on the vehicle you could have 2 different units most suvs and vans use a front and rear u it.

The thermostat or heater core could need rebuilding.

service the engine.. change oil ,filter plugs etc

did you clear the faults before each read
Diagnose Buick 3800 Engine
unusual code that

P0125 is the OBD-II generic code for the engine computer, or Engine Control Module (ECM), not detecting enough heat in the cooling system before the fuel management system can take control. The ECM has a predetermined value after you start your vehicle to expect a certain coolant temperature

P0125 OBD II Trouble Code Insufficient Coolant Temperature for Closed Loop...

ecm runs the engine cooling fans

3800V6 engine over heating and heater produces cold air
try these

EGR vale not working
overheating
inlet manifold gasket leaking
water pump fins corroded
soft radiator hoses
try a new radiator cap

internal heating
heater control tap stuck
directional actuator flaps stuck

If the heater hoses are getting hot, and the radiator is full of coolant, you could have a problem with one of the blend doors under the dash. The blend doors direct air flow thru the heater core and the vents.

ok I think this could be one of 2 things when you turn your heat on do you hear a clicking noise behind the dash if you do it could possibly be the actuator that opens and closes when you turn the temp knob from hot to cold! Also the other thing that it may possibly be could be that the heater core has gone bad and is not producing any heat to inside the vehicle but I would check the actuator switch first if you have the clicking in your dash

Oh no! What do you do when your car heater not working? How do you figure out why there's no heat in car? What if you have no heater in car? Before you start trying to figure out how to fix car heater yourself, you should know a little about how your car's heating system operates. That will help you to figure out your car heater problem and why your heater isn't working properly or even at all! So, let's talk about how your heating system functions and then about some of the more obvious reasons that it you may be getting no heat from car heater. In order to heat up the inside of your car, the heating system uses some of the excess heat produced from your engine. Actually the engine produces so much heat that if you didn't have a way to release it (the heating/cooling system in your car) it could harm and even destroy the engine! That is why the heating/cooling system is set up to remove some of the heat and keep your car running smoothly.

If it won't produce heat then you have an issue with your heater core. The heater core could be bypassed, in which case no hot coolant will get to it to produce heat inside the cabin. The heater core could be stopped up with dirt/debris, in which case the heater core can't radiate heat to produce heat in the cabin. The ducting in the dash could not be allowing the hot air to flow to the vents - therefore no heat in the cabin. I'd start with the heater core and check to see if it is bypassed. This generally happens on older vehicles because the parts can be harder to find.

Check the thermastat or your cooling fan to make sure all is working good. If your engine cant warm up, you will not produce any heat inside the car

there is a valve in the hot line to the heater core, it may not be opening. or you might have to disconnect the heater hoses and flush the heater core, stop leak will some times stop up core since tubes are very small

it takes quite a while for a diesel to warm up by just idling in order to produce any heat.you have to put them under a load (drive it), before you will get any noticeable heat.if you have a block heater, plug it in 4-5 hours before you plan on driving it and that will definitely help produce interior heat quicker.