RX400h won't start

[Imackie61]

Hi, I'm new to the forum so this may well have been answered previously. I have a 57 plate RX400h that I bought in September. I've started getting issues, where the car won't start, I.e. Ready will not display. If I disconnect the Battery and reconnect it, it will then start. Any ideas or advice please?

Thanks.

[Neil Morphett]

Hi, and welcome. I have an 08 RX400h which had the same problem in the cold last week - started fine later on in the morning. Lexus diagnosed it as a cell starting to fade on the 12v Battery - original since new - and I've replaced it (Lexus charged £95 all in), apparently 7 years is a reasonable life, do you know whether yours has been replaced ever?

Disconnecting and reconnecting shouldn't have any effect unless you think it's an issue with the connection to the Battery - which would probably have wider effects. 

[steve2006]

As above, first suspect is the auxiliary 12 Volt Battery, Lexus dealer prices are quite competitive and they will provide a fitting service on request while you enjoy the complementary hospitality in reception 

[Imackie61]

Thanks for the info. I'll give my local Lexus dealer a call tomorrow. I'm not aware that the 12v Battery has been replaced. I've looked through the paperwork history and can't see anything.

[Imackie61]

Just in case somebody else encounters a similar problem and looks at the forum, I went to the dealer and as described above the Battery had a dead cell. £95 all in to replace and fit. All seems good at this point.

[Gliderpilot]

See my previous post, it turned out to be the 3V Battery in the fob, changed that and all is now OK, but as the 12V Battery is so old I'd change it anyway. They are a peculiar Battery as it doesn't have a foot on the bottom i.e.a lip around the bottom. I've been told that it's also the same Battery as in a Toyota MR2. As this 12V Battery doesn't start the engine try looking for an AGM VRLA type Battery, these will take a deep discharge and may last longer.

[Tara]

after having the same problem myself i have found out that the CCA of the Battery should be at least CCA420. this is the engine crank amp rating, anyway I've just ordered a higher rated CCA 450 and i'll let you know later how this works.

[Gliderpilot]

2 hours ago, Tara said:

after having the same problem myself i have found out that the CCA of the battery should be at least CCA420. this is the engine crank amp rating, anyway I've just ordered a higher rated CCA 450 and i'll let you know later how this works.

But the 12v Battery does not start the engine so Cold Cranking Amps is irrelevant. It just has to have a sufficient AmpHour rating.

[Herbie]

4 hours ago, Tara said:

after having the same problem myself i have found out that the CCA of the battery should be at least CCA420. this is the engine crank amp rating, anyway I've just ordered a higher rated CCA 450 and i'll let you know later how this works.

Bit of a red herring I'm afraid Tara, and as Peter says above, the CCA rating is irrelevant.

A traditional starter motor will draw more than 300A to crank the engine of a conventional car, but hybrids aren't conventional. They have no starter motor as such and all the 12V Battery does is to boot the computers and get the car into the READY state. This takes a lot less than 300A and in fact, as you'll see from the photo below, my RX450h takes a maximum of 15.32A to get to READY. Even that 15.32A is only the inrush current and is only present for a fraction of a second - once the car is in READY mode the hybrid system powers the car and charges the Battery.

When the engine needs to run it's Motor Generator 1 (MG1) that starts it. If I remember correctly, the engine is actually spinning at about 1,000rpm before a spark is applied.

[Tara]

I bought a Battery previously from TANYA batteries after 8 months I noticed that on the odd occasion it just wouldn't start even after a charge it still sometimes failed, anyway after getting back to TANYA and explaining my occasional fail they pointed out that the one they sold me ( EUROLINE 48 ) was only 40Ah and 345A en. The one fitted was 45Ah 420en,anyway I must say they were really helpful and exchanged it fur a more powerful battery  BANNER 55Ah 460en and gave me a full refund. since the exchange (fingers crossed ) no problems.... at all.

 

[Herbie]

It may have been a faulty Battery or there may be a fault somewhere else on the car that will cause the same problem again in time, I don't know.

One thing I can promise you though, is that the higher rated cranking amps will make no difference whatsoever and whether the Battery was 30Ah 100CCA, or 130Ah 1000CCA, either one would start the car equally as well.

Glad you've got it sorted anyway  🙂