I recently purchased a 2012 IS350C from the dealer. It had been serviced at the dealer its whole life and was a very clean vehicle, all records intact. Leaving work a few days back, the car would not start, gave the typical click click click of a dead battery. It provided an early indication of a difficult start the day before...almost did not turn over. After a jump start, the car displayed the TRAC OFF and Check Engine light, and entered 'limp mode'...would not accelerate, rough idle, auto lights did not function, navigation system reverted. Towed vehicle to dealer who diagonosed as needing a new throttle body (estimate $1,500 parts and labor). I opted for a self replacement of the throttle body. Procured through O'Reilly's and replacement was pretty easy (4 bolts and 2 coolant lines). Post throttle body replacement and attempted throttle body relearn, the car will not exit limp mode nor shed the fault code.

Pre throttle body replacement, I had the followinng permanant error codes
- P2118 Throttle Actuator "A" Control Motor Current Range
- P0102 Mass or Volume Air Flow Sensor "A" Circuit Low
- P0113 Intake Air Temperature Sensor 1 Circuit High Bank 1
- P0121 Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance

Requesting any ideas on how to troubleshoot and resolve.

 

Check fuse # 6 in the engine compartment fuse box, ETCS (Electronic Throttle Control System).

 

@Nevada thanks, great advice. I missed that fuse box because it was not visible without removing the plastic engine shrouding. Sure enough, the 10A ETCS fuse was blown. Be aware that Google AI incorrectly identified the ETCS circuit as the 15A above.

Following replacement, the car fired right up, took about 10 minutes for the throttle relearn (I just let the car idle until the RPM stabilized at about 700RPM (A/C off). RPM started at about 1,500 and slowly decreased until stable. Upon start up, the check engine light extinguished after about 60 seconds, TRAC OFF remained until I manually turned traction control back on. Drove fine today!

I bench tested the old throttle body to see if it was the initial culprit, part of the problem, or actually good. Jury is still out and requesting your thoughts. A YouTube video indicated that I should see a resistance change in the circuit between two of the 6 throttle body electrical pins. I placed multi meter leads on the two end pins and observed no resistance change when manually actuating the throttle body butterfly valve. YT video indicated I would see a reduction in ohms. (Side note, pins are aligned in a single row…two pins on one end do not provide a measured reading while two pins on the other end do). Is this a valid test?

 

I believe the cause of the blown fuse was low battery voltage or the jump start.

I have seen that fuse blown on a few RX350's with dead batteries, I never had to replace the throttle bodies.

There is unlikely to be a short in the throttle control motor and certainly not a short in the throttle position sensor.