Its a tad chilly in the xj....

So 1999 XJ 4.0, new water pump, blend door, and rad hoses.
Heater works decent when everything is good. As soon as a check engine light for a leak detection pump comes on, no heat what so ever, I think the code is a P1494 I think? anyone have any ideas why I lose heat when it comes on? any help would be appreciated, its getting a lil chilly in WV and the snow will be here soon, so heat will be a plus :banghead:

Google; Jeep code+P1494

Had a similar issue, but no RENIX codes to work with, and I don't have such a LDP to begin with. However my XJ's symptoms of only blowing cold air indicated a possible solution to back-flush the heater core, which I did to solve the no-heat issue. The complete job really requires a full engine flush too, although I did not, i.e., just a partial flush by dumping out all radiator fluid for inspection, (looking good), and simply did the garden hose reverse direction flush to the core.., good to go.

I chose to not use the tricky air pressure technique over-forcing a fluid back flush to possibly rupture the core, and I also did not choose to use chemicals for the same reason..; instead just easy free flowing garden hose pressure.

Could it be that your LDP code, indicating an electrical, mechanical, or faulty/disconnected vacuum line could read one of those issues, and shut down your input of hot anti-freeze to your core? Somehow I can't put that picture together. Somehow the code to your ECU is disabling your dash switch electrical componet(s) to obtain heat? I don't consider that likely, but then I don't have the much sought after '99 model, nor am I a mechanic.

Explain what you mean by "any ideas why I lose heat when it comes on? " Are you saying the blower motor fan stops turning ?

Consider that the fan malfunction ( perhaps a short to ground ) is also triggering the P1494.

everything works good, ill have heat coming out of the vents when I am not getting the trouble code, but as soon as it the check engine light comes on, I it blows straight cold air, everything else works as it should.

Check for vacum leaks. Trace the lines from the pump to the intake manifold. Check where they run near the firewall where they could rub against things and the boots that connect them to the intake. The doors on the hvac vents are vacum controlled and loss of vacum could cause them to go into a position where they allow air to bypass the heater core.

ok, will do, Thank ya. and any idea what size the lines are? I thought about getting silicone line to replace em all