I have an 05 LS430 with 100k miles that started having an issue with the cooling fans this week.

- After going through the Lexus diagnosis, I replaced the Radiator Cap, ECT Sensor and Cooling Fan ECU, but the fans are still not kicking on without the AC turned on after the car gets to temperature
- The car never reads hot on the dash (highest it gets is just below halfway) but coolant is boiling over after the fans don't kick on
- All relays and fuses were tested and are working
- The cooling fan motors kick on with the AC, so the motors themselves aren't bad
- The thermostat and water pump were replaced with OEM units when the timing belt was done about a year ago
- There is no CEL or code

What am I missing? Any help would be greatly appreciated!

 

Likely the temp sensor(s) have an issue, there are two

 

Where is the second temp sensor? I replaced the coolant temp sensor that is below the throttle body, near the thermostat.

From the research I've done, the LS430 only has one, while the LS400 and some older Lexus models had two. The second one was connected to the radiator, but the LS430 doesn't have it.

 

Check the data stream then, see what the car thinks is happening and if it's requesting fans or not when the AC is off. If it's not requesting then it's having an issue ECU side, if it is there is a issue downstream of there.

 

How would one go about checking the data stream? I have a very basic OBD-II scanner, but no professional diagnostic tools.

Are ECM issues typical on these cars, especially in regards to the cooling system? I've heard of problems with the transmission TSB, but nothing for cooling.

 

You will need a dealer level scan tool of some sort, issues are not common at all in general for these cars