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I own a 2008 RX400H. I disconnected the Battery when the car was off the road due to a catalytic converter theft. I've now read something about an ISC reset that's, apparently, required after disconnecting the Battery?

Does anybody know anything about this?



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2 hours ago, chatmandu said:


I own a 2008 RX400H. I disconnected the battery when the car was off the road due to a catalytic converter theft. I've now read something about an ISC reset that's, apparently, required after disconnecting the battery?

Does anybody know anything about this?



I don't know what "ISC" is but usually all that needs to be reset is the sunroof, the windows and maybe the tailgate.

I think for the windows, you have to go to each door in turn and using the switch put the window all the way down, then all the way back up and hold it for a few seconds in the up position. I've never had to do it so I'm working from a vague memory of seeing it on this forum sometime in the past and I may well be wrong, so probably best to wait for someone else who knows what they're doing.

EDIT - found this and it details the reset procedure.

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Hi Rob

Just found this from when we had a 400h

Hope it answers your question.



Lexus has a TSB regarding the ISC learning procedure. Supposedly the idle speed will be off if this is not done after the Battery goes dead or is disconnected. Apparently, mileage may suffer if this is not done.


Here's the TSB -
 EG010_05.pdf ( 30.77K ) Number of downloads: 66

The TSB says you need to hook the vehicle up to the Lexus diagnostic tester (which the dealer has and you don't) but I found a post here

that shows it can be done without the tester. The tester is needed to make sure the vehicle is 181 degrees or higher, which you can do by driving it for a decent amount of time with the engine (so no stealth driving to your destination in electric only mode - drive it like you stole it so it heats up).


The instructions are as follows -

This applies to the 2006 Highlander Hybrid also.

Note that you can probably perform the procedure yourself.

The scan tool mentioned in the procedure checks the coolant temperature to make sure it is at full operating temperature and checks the engine loading to make sure the load is sufficient to charge the Battery and finally checks the status of the ISC learning parameter. It is not necessary to monitor these parameters if you do the procedure carefully.

1) Make sure the vehicle is fully warmed up. Do the procedure immediately following a long drive that runs the engine (highway speeds are best - not long gliding stealth runs at low speeds with the engine off). This will Insure the coolant temp is at FULL operating temperature - it is not necessary to actually measure the coolant temperature if you warm up the engine sufficiently and don't let the engine shut down too long and cool off before doing the procedure.

2) With the vehicle stopped and in drive, press firmly on the brake to keep the vehicle from moving and then step on the accelerator while watching the power meter (to the left of the speedometer). Press down on the accelerator to keep the needle between 1/2 and 3/4 up the scale. You will find that the engine management system will automatically limit the engine load no matter how far you press down on the pedal so the amount you press is not critical as long as it is either 1/2 scale or to the engine's self-limiting load value. Keep the engine loaded for a full 30 seconds but not longer than 40 seconds (this procedure brings the hybrid Battery up to a maximum state of charge - if you watch the Battery symbol, you willl see it tick up to a "full" display).

3) Shut off the engine and place it in park
4) Wait 5 seconds.
5) Turn the ignition key back on to display "ready"
6) make sure the A/C and heater system controls are set to off
6) Lightly step on the accelerator pedal until the engine starts -then immediately take your foot off the accelerator and let the engine run until it stops by itself.

This completes the procedure.


I've done this procedure successfully a few times now (ran my Battery dead once, and disconnected another time when trying to reset the NAV system)

The only thing I noticed (and it didn't seem to matter) was that I could not get the power meter anywhere near 1/2 to 3/4. No matter how far I depressed the accelerator, the engine management system would not let the power climb even 1/4 way. Everthing else worked as stated though.



Edited by JBPRX400h
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I think I've successfully completed the procedure. 

For anybody else that may need to complete this after disconnecting the 12V battery:

  • The power output dial didn't move when I had the car in 'drive' with a foot on brake and the accelerator to the floor. 
  • The display below the speedometer showed power going from the engine to the wheels, but the hybrid Battery did fully charge. 
  • When I put the car in 'park' and tapped the accelerator, the engine ran at various speeds for around 2-3 minutes before shutting off. 
  • After starting the car again, it pulled away quite powerfully using the hybrid Battery, which is something it's not done for a long time. Even in stop start traffic on level ground, it has been using the engine. I have disconnected the Battery on numerous occasions and wasn't aware of the need for this procedure. Perhaps this is just a coincidence, but time will tell. 

Hopefully, it has been successful and I'll see the car pulling away using the hybrid a lot more from now on. 

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