Rpm fluctuation

black-on-black · June 23, 2021

So so I've recently purchased a 2017 rx450h luxury. And of course being Lexus nothing goes wrong. However something old happened today that might be a sign of a bigger problem perhaps?

Basically I was on a hill waiting in traffic had my foot on the brake the hybrid Battery was only one bar from being fully charged. And instead of the RPM gauge going to 0 engaging the electric Battery. The RPM was fluctuating between 1000 RPM and 0 several times until I moved off. I was also Eco mode if that makes a difference.

Herbie · June 23, 2021

I've got a 2018 RX450h Luxury and I didn't even know that it's got an RPM gauge!

I have no idea what it could be but I will say that I never use Eco mode so try it in 'normal' mode and see if it still happens.

PDM · June 23, 2021

I believe the only other reason for the engine running when stationary (other than charging the battery) is to provide heat to the climate control, but I guess it wasnt cold enough weather to need that. I have never seen any of our hybrids stop and start the engine frequently when stationary and I think in eco mode it is less likely to start the engine in these circumstances.

I would monitor this, and note the date and time it happened, and next time you visit the dealer, ask them to check to see if there is anything odd in the logs on the day it happened.

Paul

black-on-black · June 23, 2021

3 hours ago, Herbie said:

I've got a 2018 RX450h Luxury and I didn't even know that it's got an RPM gauge!

I have no idea what it could be but I will say that I never use Eco mode so try it in 'normal' mode and see if it still happens.

Being that it is a 2017 it hasn't got the magic dial that switches over to a different display play when in eco to normal. Yeah that's what I tried straight away no difference.

black-on-black · June 23, 2021

2 hours ago, PDM said:

I believe the only other reason for the engine running when stationary (other than charging the battery) is to provide heat to the climate control, but I guess it wasnt cold enough weather to need that. I have never seen any of our hybrids stop and start the engine frequently when stationary and I think in eco mode it is less likely to start the engine in these circumstances.

I would monitor this, and note the date and time it happened, and next time you visit the dealer, ask them to check to see if there is anything odd in the logs on the day it happened.

Paul

I just had a thought about a couple of things that could be.

1. Third party new Battery supplied by third party dealership is not sufficient to give charge to the petrol engine. I shall contact them and find out what Battery they put in. The original Lexus Battery was flat as a pancake apparently.

2. Alternator is not giving enough charge to the Battery and is defective perhaps?

3. I'm actually driving too efficiently and not engaging the petrol engine enough to give sufficient charge to the Battery.

4. This is a long shot but you never know it could be the air con compressor interfering with the charging of the Battery somehow?

Barry14UK · June 23, 2021

The auxiliary Battery does not charge the Battery, it only powers up the traction Battery that does the heavy lifting.

Car doesn't have an alternator but a generator which powers the traction Battery which in turn boosts the 12v Battery.

Unlikely you are driving too efficiently as traction Battery well charged and would supply 12v Battery and if this falls traction Battery not well charged motor would top it up.

A faulty 12v Battery can cause problems.

Herbie · June 23, 2021

Well, to answer some questions:

The 12V Battery will be fine. Original fit batteries are only small capacity anyway because hybrids don't have starter motors. A conventional starter motor can draw upwards of 300A when cranking the engine but the 12V Battery in a hybrid only boots the computers and does a couple of other things to get the car into READY mode, which only takes about 20A.
Hybrids don't have alternators (or anything else that would normally be driven by a belt from the engine* - Imagine losing power steering in the middle of a turn because the hybrid system decided to shut off the petrol engine at that moment). We have a DC/DC converter that takes power from the 288V traction Battery and converts it to about 14.5V to run all the 12V systems and keep the 12V Battery charged. It would be very unusual for this to be faulty.
This just can't happen.
Again, the aircon compressor is driven by an electric motor, not a belt. It's actually a 500V 3-Phase AC variable frequency motor, again powered by an inverter/converter and would be unlikely to cause something like this.

* The only thing driven by a belt is the water pump that circulates engine coolant and provides the heat for the cabin heater.

mikey2001 · June 23, 2021

The RPM tachometer should show up in 'Sport' mode by default. If the gauge doesn't show, it can be configured in the 'Meter settings' of the multi-function display via the steering wheel button controls.

black-on-black · June 23, 2021

6 minutes ago, mikey2001 said:

The RPM tachometer should show up in 'Sport' mode by default. If the gauge doesn't show, it can be configured in the 'Meter settings' of the multi-function display via the steering wheel button controls.

It's always on no matter what mode. I thought it was odd being that every review I saw on YouTube of RX the dial changed. Can you please tell me exactly how to change this?

mikey2001 · June 23, 2021

I'm doing this partly from memory, so this may be incorrect:

Press the left/right arrrows buttons on the right-hand side of the steering wheel until you get to an icon that looks like a cog. Once you get to this icon, use the up/down arrow buttons until you get to 'Meter Settings'. Press the Enter button (the one with the dot in the middle). Using the up/down buttons again, you should see an item named 'Tachometer setting'. Press the Enter button again and you should have a choice of:

Change according to driving mode (this will show the hybrid system in Eco and Normal, tacho in Sport)
Always tachometer
Always Hybrid System

black-on-black · June 23, 2021

1 hour ago, mikey2001 said:

I'm doing this partly from memory, so this may be incorrect:

Press the left/right arrrows buttons on the right-hand side of the steering wheel until you get to an icon that looks like a cog. Once you get to this icon, use the up/down arrow buttons until you get to 'Meter Settings'. Press the Enter button (the one with the dot in the middle). Using the up/down buttons again, you should see an item named 'Tachometer setting'. Press the Enter button again and you should have a choice of:

Change according to driving mode (this will show the hybrid system in Eco and Normal, tacho in Sport)

Always tachometer

Always Hybrid System

I made a video and was doing it all wrong. 😁 I'll give it try next time I drive. At times metering mode was greyed out. 🤔

mikey2001 · June 23, 2021

39 minutes ago, black-on-black said:

I made a video and was doing it all wrong. 😁 I'll give it try next time I drive. At times metering mode was greyed out. 🤔

I'll double check mine tomorrow and see what the settings are, just to be sure. My car is a 2019 model but pre-facelift, so I imagine the settings should be similar to yours.

ColinBarber · June 23, 2021

9 hours ago, black-on-black said:

The RPM was fluctuating between 1000 RPM and 0 several times until I moved off. I was also Eco mode if that makes a difference.

how many seconds between the fluctuations?

mikey2001 · June 24, 2021

12 hours ago, mikey2001 said:

I'll double check mine tomorrow and see what the settings are, just to be sure. My car is a 2019 model but pre-facelift, so I imagine the settings should be similar to yours.

Hi Robert,

I watched your video and I've just checked my multi-function display, and what I said before seems to be correct, at least for my car.

When you're in the list of Settings (Language, Units, EV, etc.), keep on pressing the down button and you should reach 'Tachometer Settings'. If you press Enter on this, you should then be given the 3 options to change your display. I would ignore the Switch Settings option for now as this is something different and doesn't affect the hybrid system/tachometer display.

black-on-black · June 24, 2021

12 hours ago, mikey2001 said:

Hi Robert,

I watched your video and I've just checked my multi-function display, and what I said before seems to be correct, at least for my car.

When you're in the list of Settings (Language, Units, EV, etc.), keep on pressing the down button and you should reach 'Tachometer Settings'. If you press Enter on this, you should then be given the 3 options to change your display. I would ignore the Switch Settings option for now as this is something different and doesn't affect the hybrid system/tachometer display.

I've managed to set up the way I like now. 👍😁 I also put a how to. On my YouTube channel because really I could not find any clear instructions on YouTube how to do this. https://youtube.com/shorts/4eQKQG3pnKI?feature=share

Herbie · June 24, 2021

43 minutes ago, black-on-black said:

I've managed to set up the way I like now. 👍😁 I also put a how to. On my YouTube channel because really I could not find any clear instructions on YouTube how to do this. https://youtube.com/shorts/4eQKQG3pnKI?feature=share

Never mind that - how have you gone on with the actual fault and the questions that brought you here in the first place? :rolleyes:

black-on-black · June 24, 2021

7 minutes ago, Herbie said:

Never mind that - how have you gone on with the actual fault and the questions that brought you here in the first place?

Well I rang the third party dealership. And they said the service department would call me back. That never happened. 🙄 yesterday. And today I really didn't have the time to follow up. So what I'm going to do is take a peek underneath the bonnet and take a look at Battery and call Lexus to check it's the correct specification. If it isn't the correct specification then the third party dealers going to have to compensate me for a new Battery or some other arrangement.

To be continued...

Herbie · June 24, 2021

1 hour ago, black-on-black said:

So what I'm going to do is take a peek underneath the bonnet and take a look at battery and call Lexus to check it's the correct specification

My 2018 has a 60Ah Battery in it. I'm not sure of the CCA (Cold Cranking Amps) rating but it doesn't matter because, given that the car doesn't have a starter motor the Battery doesn't have to crank the engine.

You can basically use a golf trolley Battery, or a mobility scooter Battery, or even a lawn mower Battery to get these cars running so I really can't see the Battery being the problem. I suppose it could be a faulty Battery but the chances of it being 'under spec' or not up to the job are extremely low.

Good luck and don't forget to keep us informed :thumbsup:

black-on-black · June 25, 2021

Okay the Service department finally got back to me. It's a new RBLS4005 BOSCH S4 027 Battery. Next step will be to book it into Lexus dealership and claim on on the warranty to find out what happened and why?