JDM UCF21 “Engine Main” relay missing?

[Fi7e]

Just checking to see if this is normal. Figured my car either wouldn’t run or have CEL’s on if it wasn’t.

 

 

[RX400h]

Do you have access to the wiring diagram? I agree that it is likely that the fuse should be there.

[paulo57509]

You have a Celsior so it may be normal.  It's not normal on a NA LS.  My '98 has a relay in that position.  Here is the circuit that contains the Engine Main Relay:

From factory 1998 Lexus LS400 Electrical Wiring Diagrams

Double-click the image so you can see it.  Essentially, the relay powers the electric cooling fan and the front seat heater (if equipped).  This relay doesn't appear to run thru any of the many ECU's that an LS has.  That's why you won't see any trouble codes.

A previous owner probably removed the relay as an expedient to taking the time to troubleshoot whatever the issue it was causing.

Quick check: Does the cooling fan come on?  If you have heated seats, do they warm?

[Fi7e]

12 hours ago, paulo57509 said:

You have a Celsior so it may be normal.  It's not normal on a NA LS.  My '98 has a relay in that position.  Here is the circuit that contains the Engine Main Relay:

From factory 1998 Lexus LS400 Electrical Wiring Diagrams

Double-click the image so you can see it.  Essentially, the relay powers the electric cooling fan and the front seat heater (if equipped).  This relay doesn't appear to run thru any of the many ECU's that an LS has.  That's why you won't see any trouble codes.

A previous owner probably removed the relay as an expedient to taking the time to troubleshoot whatever the issue it was causing.

Quick check: Does the cooling fan come on?  If you have heated seats, do they warm?

Interesting, thank you. My fan does turn on, I just checked that 2 days ago and I do not have heated seats…

[Fi7e]

Resolved. My car doesn’t need a “Main Engine” relay.

[paulo57509]

On 4/7/2024 at 1:29 PM, Fi7e said:

Resolved. My car doesn’t need a “Main Engine” relay.

What did you do to solve the problem?  It might help someone else in the future.

[Fi7e]

I didn’t do anything to resolve the “problem”. My Celsior doesn’t need that relay. My fan is hydraulic and I don’t have heated seats.