[donaldp]

Today, while driving on the freeway, my Check Engine light came on and a message appeared that said something like "Reduced Power Mode". I continued driving for about ten minutes and parked. I heard the fan going at a high noise level. The fan continued going for quite a while after turning the car off. After about an hour, I drove 30 miles to home. I never saw the "Reduced Power Mode" message again, and could not confirm power levels, due to heavy rains. At home, the fan stayed on for about ten minutes and then finally shut off. The coolant temperature on the dash display, never left the minimum level of 160 degrees so I'm guessing the thermostat is stuck open. After about two hours, I started the car, moved if 50 feet into the garage and the fan stayed on blaring for about ten minutes after moving the car those 50 feet.

Does this sound like a thermostat issue of a Temperature Sensor issue, or something else? If it is simply the thermostat, and I replace it, will the check engine light turn off?

Nine year old 2017 ZL1 with 96,000 miles.

[RIPws6]

Originally Posted by donaldp

Today, while driving on the freeway, my Check Engine light came on and a message appeared that said something like "Reduced Power Mode". I continued driving for about ten minutes and parked. I heard the fan going at a high noise level. The fan continued going for quite a while after turning the car off. After about an hour, I drove 30 miles to home. I never saw the "Reduced Power Mode" message again, and could not confirm power levels, due to heavy rains. At home, the fan stayed on for about ten minutes and then finally shut off. The coolant temperature on the dash display, never left the minimum level of 160 degrees so I'm guessing the thermostat is stuck open. After about two hours, I started the car, moved if 50 feet into the garage and the fan stayed on blaring for about ten minutes after moving the car those 50 feet.

Does this sound like a thermostat issue of a Temperature Sensor issue, or something else? If it is simply the thermostat, and I replace it, will the check engine light turn off?

Nine year old 2017 ZL1 with 96,000 miles.

Sounds like the thermostat to me although I just got the CEL, no reduced power mode and I noticed the engine temp was at about 9:00 instead of the normal 11:00 position on the gauge.

Get a code scanner hooked up to it. If you don't have one, go to an AutoZone or an O'Reilly's. You're looking for a PO128 code.

The fact that you stated the fan came back on when you restarted the car might be more telling of a Temp Sensor. Both have similar symptoms.

If you have a temp sensor issue you will probably see one of three codes.
P0117: Engine Coolant Temperature Circuit Low Input
P0118: Engine Coolant Temperature Circuit High Input
P0119: Engine Coolant Temperature Circuit Intermittent

[speedyink1]

Sounds like the temperature sensor to me

[donaldp]

Thanks! Bought the Code Scanner and found the code P0128, so it's the Thermostat.

[RIPws6]

Originally Posted by donaldp

Thanks! Bought the Code Scanner and found the code P0128, so it's the Thermostat.

Thanks for the update! The part is not expensive and a quick fix.
Hoping you’re back to normal cruising soon!

[lowke]

My fan kept running after shut down in December. 2021 ,V6, 83k miles. I drained the radiator and replaced thermostat. No problems since.

[ZLRob]

If you have a P0128 then replace the thermostat, as they have been known to cause issues on the early gen Z's. I replaced mine shortly after I did my engine build with a DMS housing and a 186* Corvette LS3 thermostat and have never had a problem with temperature regulation ever since. This may be a great time for you to do the same. As it gets rid of the new gen style small stat that is being used on the LT engines and you'll give your housing a better protection from the belt taking it out if it ever comes to slip off or snap off the pulleys.