Computer Issues In '99 Rx 300 -- Help!

[Andrea V.]

I have a new problem in my '99 RX 300 - there seems to be a computer gremlin! Each time the car is turned off, the trip computer, MPG, etc. all reset, the CD player "loses" its place, etc.

If this was my laptop, I'd question whether it was the PRAM. Does the Lexus have a similar set up, where a battery other than the main battery feeds a RAM or ROM memory? I've had it into my indy shop, but they couldn't find a code. Other than taking it to the dealer, what are my options? Anyone?

[blk_on_blk]

"engine control modules use a common Toyota-branded NEC µPD70F3155 32-bit microprocessor as the primary source of computing power." ...that's the most definitive explanation of Toyota's ECM that I could find. Maybe you will get more from how they describe the system as they compare the Prius hybrid to conventional Toyota ECM's (which I'm sure the RX uses since it has their tried and true 1MZFE engine).

http://www.techonline.com/product/underthehood/199501619

[Karl K]

I wonder if there is a separate fuse for that ?

[wwest]

I have a new problem in my '99 RX 300 - there seems to be a computer gremlin! Each time the car is turned off, the trip computer, MPG, etc. all reset, the CD player "loses" its place, etc.

If this was my laptop, I'd question whether it was the PRAM. Does the Lexus have a similar set up, where a battery other than the main battery feeds a RAM or ROM memory? I've had it into my indy shop, but they couldn't find a code. Other than taking it to the dealer, what are my options? Anyone?

Have you yet removed, cleaned and burnished the battery connections and battery posts??

Let us know the results.

[RX in NC]

Yep, I'm betting it is indeed your battery, especially if the battery is the factory original.

That's an inexpensive and easy fix, so here's hoping that's exactly what it turns out to be....

[blk_on_blk]

I guess that prompts the question regarding if the battery is showing any signs of age/failure. Does it hesistate or is it slow to turn over and start in the mornings? Is the interior light dim when the engine is off? Any corrosion build up on the terminals? If not, and if the battery is strong, I wouldn't think it would be the battery, for it has to be pretty low and weak to shut down the ECM.

Then again, I've seen freaky things happen with batteries: inconsistent shorts in cells, sporatic voltage problems, and random recharging issues. If it's the originial one, or even several years old, it's a relatively cheap investment to replace it and ensure it's not the battery.

[mikey00]

I guess that prompts the question regarding if the battery is showing any signs of age/failure. Does it hesistate or is it slow to turn over and start in the mornings? Is the interior light dim when the engine is off? Any corrosion build up on the terminals? If not, and if the battery is strong, I wouldn't think it would be the battery, for it has to be pretty low and weak to shut down the ECM.

Then again, I've seen freaky things happen with batteries: inconsistent shorts in cells, sporatic voltage problems, and random recharging issues. If it's the originial one, or even several years old, it's a relatively cheap investment to replace it and ensure it's not the battery.

RX often has problems like this without the battery showing any other signs of failure. There have even been cases of the battery testing ok by a auto repair shop but still causing similiar problems. I am not sure if this is one of the characteristics of the original Panasonic battery or a characteristic of the RX sensitive electronics.

You didn't mention it, but I bet your clock is also resetting. This almost always is caused by the battery.

[blk_on_blk]

Just to add to the information here, I spoke with a co-worker with a background in automotive controls development... he said older cars did use PRAM (I'm guessing around the ODBI era), but newer ones use dedicated proprietary circuit boards. Knowing that Toyota has it's "common" NEC 32-bit microprocessor as a basis for their ECM, I'm going to say it's a proprietary control system. My coworker was saying that a manufacture's ECM is essentially a 'black-box' of integration based on their own engineering and cooperative endeavors with other vendors... i.e., they aren't going to tell you it's foundation.

Let's hope you've just got a quirky battery and a new one will remedy everything.

[lenore]

When my battery failed as others have said the clock would loose time, however everything else worked fine... Good luck with the battery hopefully being your solution... Costco sells a replacement that will be cheap and last a long time...