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battery problems. or is it ?

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i've noticed there is a thread about a flat Battery problem in november 2020, but my problem is similar but slightly different. ( all will become apparent).

i have a CT F-sport 2020 model with a few extras. the way things are at the moment it isn't getting driven very much. as i am retired now i don't get to travel to work and back so it's only got 350 miles on the clock. about 3 months ago i went to start the car and the Battery was flat, totally my fault, hadn't used it or started it for roughly a month or so.called out the friendly AA, bit embarrassing as i used to work for them before i retired, on the recovery side.quick jump pack and away it went, he tested my jump pack at the same time and it was fine.i have tried to go out and start it every week or so to try to keep it topped up.i have a tracker fitted so i am able to keep an eye of the voltage in live time on my it was showing 10.6 volts went out to start it and it just wouldn't even turn over, it dropped to 6,2v when trying to start. attached my jump pack by the approved method and away it went and it showed 15.0v when the engine was running, so i realised i needed to take it for a short run.

now this is where the problem is. i was going to take it for a run to the next town and back which is a total of about 8 miles, before anybody says anything it is where the nearest large tesco is.when the ignition is switched on or when it is running i get two messages with both showing the yellow triangle.

one says ' check hybrid system' hybrid system malfunction.stop in a safe place and check owner's manual.

the other says Pre-collision system malfunction. visit your dealer.

it changes between the 2.

is there a way of resetting the system i don't have a code reader and i was going to do the old trick we used to do of disconnecting the Battery for a minute or so and then reconnecting, but as it's a hybrid system i thought it might have messed things up.

any suggestions would be greatly appreciated. thanks

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Personally I wouldn't recommend you spend any of your own time trying to troubleshoot an issue with what is effectively a brand new car.

Hand it over to Lexus and let them sort it.

All the best.

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What Ricky said. It may simply be that letting the Battery run low has confused the car, I know on the newer vehicles it's not generally a good idea to ever disconnect the Battery if you can avoid it.

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ok guys thanks for both your comments. i was starting to think that way has to be checked out by the AA tomorrow as is normal practice will leave it to them and the dealer.

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I'll almost guarantee that it's the 12V Battery too low and sadly, an 8 mile run just isn't enough to charge it back up. Letting it get so low may even have damaged it or reduced its capacity and/or its ability to recover.

If you worked for the AA then you'll know that a conventional car starter motor will draw 300A or more as it cranks the engine. Hybrids don't have a starter motor and the 12V Battery only has to boot the computers to get the hybrid system running and into READY mode, a process that takes less than 20A, so if the Battery can't even supply that....


During the first lockdown the advice on Toyota's website was to put the car in P(ark) (NB: don't put it in Neutral because the traction Battery doesn't get charged) and into READY mode for 60 minutes per week. The petrol engine will start and stop as necessary to keep the 12V Battery charged up. Don't leave the car unattended when doing this because READY mode is the hybrid equivalent of a conventional car with engine idling, so someone could drive it away. Simply sit in it reading the paper or whatever, but don't put the radio on or other electrical drains or you'll not get the full benefit of the exercise.

EDIT: I get the impression it may be the first hybrid you've had because you talk of the Battery not being able to "turn over the engine".

If I'm wrong and I'm sort of 'teaching my granny to suck eggs' then I apologise and you can ignore the rest of this post.

However, if I'm right, you may be interested to know that hybrids don't have starter motors or alternators, and anything that would normally be driven by a belt from the engine is driven electrically because the engine doesn't run all the time. Power steering, coolant circulation (to provide cabin heat), and the aircon compressor are all driven by electric motors.

As mentioned earlier, the 12V Battery boots the computers to get the car into READY mode, at which point you can drive off on Battery power alone if you so wish. When the hybrid system wants the petrol engine to run, it energises MG1 (motor/generator 1) and uses it to spin the petrol engine up to 1000rpm before the ECU applies fuel and a spark to fire it.

The 12V Battery is kept charged up by the DC/DC converter that takes the high voltage and reduces it to about 14.5V.

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thankyou for your reply and it was very informative.

just a couple of points. firstly i was not a mechanic in the AA i was recovery and we did not need to have any knowledge about the workings of a car as we didn't diagnose or attempt repairs we just ' lifted and shifted' so most of what you said i had no idea about.we weren't even allowed to change a wheel. the one thing that did surprise me is the fact there is no alternator or starter.

i have owned 2 other hybrid lexus's but i never had this problem before as i used to work, so the cars were used regularly and travelled approx 40 miles each day plus the extra mileage on days of the lexus's and it's associated problems i had with it is well documented on this forum, but it wasn't electrical/engine problems.

lastly it's a pity lexus or toyota didn't mailshot owners to tell them of the advice that should be followed during this lock down as again i had no idea about it and i'm sure i'm not alone in thinking that.


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