Close
QUESTIONS

RepairPal is your advocate for car care advice and guidance

Q: Troubleshooting help with a coolant thermostat problem. P0128 code. on 2002 Lexus ES300

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
The check engine light used to go off and on periodically. A month ago it came on and has not gone off. the code reads P0128, a coolant thermostat problem present. However, the engine temp gauge on my dash has been working perfectly normal this whole time. I am guessing it is a faulty sensor since, like I said, the check engine light used to go on and off periodically. What troubleshooting things can I do to find the solution?
No car image 94a1663db56199c5353592009e34aaa51078a2469bed068bb8d6f0ba43accf97
Get a Repair Estimate
Guaranteed by certified locations nationwide. Learn more
RepairPal estimates are guaranteed at over 1,700 quality certified locations nationwide. Learn more
Monitor the readings for coolant temp. sensor (for PCM-NOT fan) WITH scanner(live data) and see if it's opening to soon. Car may not be warming up fast enough for OBDII specs , and setting the code. Has t-stat ever been changed (with Toyota/Lexus part)?
Is there a cheap way to monitor the coolant temperature? I don't have a scanner. I would consider buying one if I needed to however. It is my wife's car and she doesn't think the thermostat has ever been replaced. She inherited the car maybe 5 years ago.
P0128 is indicating the engine is not warming up fast enough (simply put) , I would try replacing the thermostat first , I would also recommend getting the thermostat from the dealer. YES , it will seem outrageous compared to aftermarket , but 1) you know you're getting the right one , 2) the original lasted 12 years. Also factory coolant. IF you are saving the labor $$ by doing it yourself , get the best parts!
Find Out Why Your Check Engine Light Is On
Didn't find what you were looking for?