I have a 2000 Grand Cherokee 4x4 Laredo 6cyl. When I'm driving down the highway at night I notice that my Headlights flicker from time to time and the heater fan also cuts out. This flickering happens every few minutes or so I would say and it only lasts for a fraction of a second. Also, i'm not sure if this has anything to do with this problem but the heater also doesn't always blow warm air. It will get warm pretty quickly but it never gets hot like it should and it will sometimes blow cold air even after its been blowing warm air. I replaced the thermostat hoping it was going to be an easy and painless fix but no such luck. Any help would be greatly appreciated.

 

I had a similar problem with my '97 Cherokee sport, except not only were the lights flashing, and the AC/heater fan would slowdown, but the radiator cooling fan would speed up, and it wouldn't downshift (auto) when stopping.

Thanks to this forum, I discovered it to be a bad ground to engine/battery. Check your negative cable terminal, make sure the connections are good. Check the negative ground where it attaches from negative cable to fender, make sure it is connected and tight, mine was loose. I am not sure if the Grand is any different here.

But in my case, after fixing the other items mentioned, I found it to be the (braided strip) engine to firewall ground, it was slightly frayed at one connection. Hope this helps.

 

I'll check that out as soon as its more than 10 degrees outside! The cooling fan just went out about a month ago and the Jeep overheated on me.