# Why is my car overheating at idle or in heavy traffic? **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** cherokee, overheating, jeep, fans, radiators\ **Created:** [August 30, 2010, 8:12pm UTC](https://community.cartalk.com/t/why-is-my-car-overheating-at-idle-or-in-heavy-traffic/54414 "2010-08-30T20:12:42Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![zmackoviak](https://avatars.discourse-cdn.com/v4/letter/z/9f8e36/32.png) [@zmackoviak](https://community.cartalk.com/u/zmackoviak)\ **Post date:** [August 30, 2010, 8:12pm UTC](https://community.cartalk.com/t/why-is-my-car-overheating-at-idle-or-in-heavy-traffic/54414/1 "2010-08-30T20:12:42Z")
I have a 2002 Jeep Grand Cherokee. The check engine light is not on. However the car begins overheating when sitting at idle. The radiator fan does not run at any point. Could a bad thermostat cause the radiator fan to not run? ---
**Author:** ![VDCdriver](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/vdcdriver/32/30_2.png) [@VDCdriver](https://community.cartalk.com/u/VDCdriver)\ **Post date:** [August 30, 2010, 8:24pm UTC](https://community.cartalk.com/t/why-is-my-car-overheating-at-idle-or-in-heavy-traffic/54414/2 "2010-08-30T20:24:46Z")
No, a bad temperature sensor or two is the likely culprit. I suggest that you get this attended to very promptly. Continued overheating is slowly but surely reducing the life of your engine. ---
**Author:** ![zmackoviak](https://avatars.discourse-cdn.com/v4/letter/z/9f8e36/32.png) [@zmackoviak](https://community.cartalk.com/u/zmackoviak)\ **Post date:** [August 30, 2010, 8:38pm UTC](https://community.cartalk.com/t/why-is-my-car-overheating-at-idle-or-in-heavy-traffic/54414/3 "2010-08-30T20:38:24Z")
A bad temperature sensor wouldn’t trigger the check engine light? ---
**Author:** ![VDCdriver](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/vdcdriver/32/30_2.png) [@VDCdriver](https://community.cartalk.com/u/VDCdriver)\ **Post date:** [August 30, 2010, 9:47pm UTC](https://community.cartalk.com/t/why-is-my-car-overheating-at-idle-or-in-heavy-traffic/54414/4 "2010-08-30T21:47:10Z")
Maybe yes, maybe no. In any event, the thermostat has nothing to do with the cooling fan failing to run, so you can dismiss that theory. ---
**Author:** ![kizwiki](https://avatars.discourse-cdn.com/v4/letter/k/7cd45c/32.png) [@kizwiki](https://community.cartalk.com/u/kizwiki)\ **Post date:** [August 31, 2010, 12:03am UTC](https://community.cartalk.com/t/why-is-my-car-overheating-at-idle-or-in-heavy-traffic/54414/5 "2010-08-31T00:03:37Z")
The radiator fan is not working. There is no way any manufacturer would have spent five cents on this assembly were it not absolutely necessary. Check your fuses first. ---
**Author:** ![oldtimer-11](https://avatars.discourse-cdn.com/v4/letter/o/e79b87/32.png) [@oldtimer-11](https://community.cartalk.com/u/oldtimer-11)\ **Post date:** [August 31, 2010, 2:52am UTC](https://community.cartalk.com/t/why-is-my-car-overheating-at-idle-or-in-heavy-traffic/54414/6 "2010-08-31T02:52:05Z")
You probably have a bad fan relay or a bad fan control module. Does the fan(s) kick on when you put on the a/c. ---
**Author:** ![waterboy](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/waterboy/32/764_2.png) [@waterboy](https://community.cartalk.com/u/waterboy)\ **Post date:** [August 31, 2010, 2:59am UTC](https://community.cartalk.com/t/why-is-my-car-overheating-at-idle-or-in-heavy-traffic/54414/7 "2010-08-31T02:59:51Z")
The radiator fan does not run, the car overheats, yes oldtimer has it down unless of course the fan motor is shot. Question 1 is the fan motor run by a belt or an independant motor? Low coolant, and bad pressure are also possibilities. ---
**Author:** ![geeaea](https://avatars.discourse-cdn.com/v4/letter/g/6f9a4e/32.png) [@geeaea](https://community.cartalk.com/u/geeaea)\ **Post date:** [August 31, 2010, 3:57am UTC](https://community.cartalk.com/t/why-is-my-car-overheating-at-idle-or-in-heavy-traffic/54414/8 "2010-08-31T03:57:29Z")
Follow the wires from the fan (use the color codes on the wire). Find the relay and jump it out. If the fan runs, the relay is most likely bad. If it doesn’t it could be the fusable link or the fan is shot, or both (there’s typically a reason what the link goes bad. The fan is wired hot, iirc. I believe that the relay provides the ground with a trigger from the PCM. ---
**Author:** ![MikeInNH](https://avatars.discourse-cdn.com/v4/letter/m/a587f6/32.png) [@MikeInNH](https://community.cartalk.com/u/MikeInNH)\ **Post date:** [September 1, 2010, 1:18am UTC](https://community.cartalk.com/t/why-is-my-car-overheating-at-idle-or-in-heavy-traffic/54414/9 "2010-09-01T01:18:02Z")
[quote]A bad temperature sensor wouldn’t trigger the check engine light?[/quoye] Sure it can…the fan doesn’t kick on…the car over heats…the over heated can trigger the CEL.