I was chasing code C1231 Steering Angle Sensor error for months: replaced the Spiral Yellow Sensor thingy (new / part no 84306-33070), replaced the whole turning assembly (used / part no 84310-6A880) but still the dreaded VSC TRAC and VSC OFF won't go away. Followed the Repair Manual and gave up since the last step is "Replace VSC ECU" 
(see attached C1231 pdf). By chance I was reading the Circuit Diagram and was surprised that the Steering Angle Sensor is powered by 20A fuse labelled AHC-IG! Because in the Owner's Manual (and also repair manual) AHC-IG is marked "No Circuit" since mine is LC100 without AHC not LX470. Decided to trust the Circuit Diagram and replaced the 20A minifuse with brand new one. Voila, VSC TRAC and VSC OFF warning lights gone now 
Oh my, how a simple solution it was all this time 
Fig 1: VSC TRAC & VSC OFF warning when turning on car
Fig 2: Toyota Wiring Diagram showing Steering Angle Sensor is powered by 20A fuse labelled AHC-IG
Fig 3: No more VSC TRAC & VSC OFF warning lights! All by simply replacing 20A fuse marked AHC-IG from the left-kick panel
(see attached C1231 pdf). By chance I was reading the Circuit Diagram and was surprised that the Steering Angle Sensor is powered by 20A fuse labelled AHC-IG! Because in the Owner's Manual (and also repair manual) AHC-IG is marked "No Circuit" since mine is LC100 without AHC not LX470. Decided to trust the Circuit Diagram and replaced the 20A minifuse with brand new one. Voila, VSC TRAC and VSC OFF warning lights gone now Oh my, how a simple solution it was all this time
Fig 1: VSC TRAC & VSC OFF warning when turning on car
Fig 2: Toyota Wiring Diagram showing Steering Angle Sensor is powered by 20A fuse labelled AHC-IG
Fig 3: No more VSC TRAC & VSC OFF warning lights! All by simply replacing 20A fuse marked AHC-IG from the left-kick panel
