I've recent purchased a 2007 Prius and it's constantly triggering Check Engine Light (CEL) on and off; The CEL doesn't stay on for more than 24 hours. I've scanned the code and it turns out to be "P1121" which seems to be the common read for 2nd generation Prius. I really like the car and want to "baby" it yet the tricky part is that the CEL doesn't stay on. I drove it for more than 500 miles and the vehicle rides perfectly fine with 50 MPG. I was wondering if I should fix the coolant valve right away or wait until I sense more, actual problems.
1. Check the engine coolant level in the overflow container as well as the radiator itself (must remove the large black plastic cover over the radiator for access to the radiator cap.) 2. If the coolant level is full in both places, then the engine coolant valve needs to be replaced. If coolant is low, that may have been the reason for the DTC being logged. 3. Depending upon the position in which the engine coolant valve is stuck, you may notice poor cabin heater performance or the engine warmup will be slightly longer than normal, which has mpg and emissions implications. Given the above, it's up to you and your standards of vehicle maintenance to decide when that work should be performed.
Welcome to Prius Chat! Do exactly what Patrick said. If you do that, the code should go away and the problem should be solved. Yes, it is a common thing on Gen II. Yes, low coolant will trigger it, and yes a bad valve will also trigger it. Luscious Garage | Blog | Prius P1121: Coolant Flow Control Valve Position Sensor Stuck Best of luck to you, Ron (dorunron)
