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Q: Check engine light, ETC warning light come on; temp gauge drops to 0; why? on 2009 Jeep Grand Cherokee

Problem seems to cycle - driving along, suddenly the check engine light comes on along with the electronic throttle control warning light, as the temp gauge drops to zero - which triggers the Check Gauges warning light to come on. Drive more, stop a few times, ETC light goes off, temp gauge starts working again. Check engine light stays on for a while, then goes off. Some miles/hours later, cycle repeats. No indication of trouble in engine behavior, sound, etc. Tried replacing gas cap (2x). Dealer replaced thermostat. Still going on. Any ideas?
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could be a cts problem [coolant temp sensor] I agree with #1 check to see if there are any codes
When dealer last had it for this same problem (9/13/13), they wrote "Engine light on - found faults for cooling system performance," then "checked for coolant leaks found leaking t-stat, replaced, flashed PCM to latest software for throttle body updates." But the whole cycle began again within a few days of this service. Currently vehicle is at dealer - but all warning lights were off this time, service advisor said, if the lights aren't on there won't be any codes. I asked, you mean it doesn't store codes? He replied, maybe.

I cannot link the recurrence of this to any pattern in terms of speed, braking, etc. I understand possible link to CTS but don't see how that would also relate to ETC warning - they always come together, and go away together. Sound like software to me. I will post any further info as I get it.

Just heard back from dealer - SA claims, no engine light, no code. Next time it happens I will take it somewhere to read the codes while the situation is active.
Finally have a resolution on this. First, note that we were never able to get any codes. I took the car to an independent shop while the check engine light and ETC warning lights were on, the temp gauge had dropped to zero, and the "Check Gauges" warning was showing. Engine was running as this was verified by the shop tech. He said he had to shut off the engine to hook up the code reader. We did this, then when we restarted the ETC warning light and Check Gauges warning were both gone, but the check engine light was still on. There were no codes. Repeat - no codes. We were all stumped. Later, this same tech said, maybe the temp sending unit is going bad.

Side note - I once had a 96 Grand Cherokee and the oil temp sensor was going bad - very similar symptoms. Stop at a light, oil pressure gauge would drop to zero, Check Gauges warning would show up, check engine light came on. Replaced the oil temp sensor and everything was fine.

Back to the 09 GC: we replaced the temp sensor sending unit 10 weeks ago. There has been no recurrence of this problem. We still do not understand why the ETC warning light would come on, but it stopped along with the Check Gauges warning, the temp gauge pegging left, and the check engine light coming on.

I consider this problem solved. I also find it very interesting that it was solved by an independent garage technician who had a good hunch, when 3 visits to the Jeep dealer in Yuma failed to figure out the problem. Enough said.
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