B1503 DTC

Yesterday the red temperature warning light came. Car was parked in the garage all day. Only after I turned on and car idle for 1 minute light came on.
Techstream showed DTC 1503 exhaust heat management warning detected.
Tried clearing but DTC still showed up.
I did remove the AC amplifier before this ( unjacked and reinserted ) because I was testing the amplifier on a next car.
Any help on solving much appreciated.

 

Car is a Prius c 2013

 

Just an update the temp light is going off when I turn the car off. After I put the car on or in ready the light takes approximately 1 minute before it comes back on.
I gave the car a little run and the temp Went up to 60 deg.C not seeing any sign of overheating.
Put the ac in cold/hot setting and it's working fine.
Any thoughts anyone.

 

I resolved the issue. I disconnected the 12V battery negative for a few minutes, pump the brakes a few times waited about 10 minutes after, reconnected the battery and presto of t worked no more temperature light. Cleared the code from the history car is working wonderful.