ScanGauge II – Prius Gen 4 XGauges – Observations on Hybrid Battery Current

The first few XGauges for the Gen 4 Prius are now being published. I was fortunate enough to be in a position to do some preliminary real world testing of some of these. Previously, with the Gen2 and Gen3 models, the Hybrid Battery State of Charge (SOC) and Battery Current (BTA) were two XGauges that many PriusChat members found useful.

This post focuses on my initial observations of BTA on a Gen4 and to compare them with my previous experiences with the Gen3 and Gen2, on which I have posted previously in 2011 and 2009 respectively.

The XGauge I tested works on my 2016 Gen4 in the UK. I can see no reason why it should not work elsewhere, but YMMV!:

TXD: 07DF0153
RXF: 432180000000
RXD: 1810
MTH: 000100018000
Name: BtA (a.k.a., BCA, BTA, can be anything you like)

The hybrid (a.k.a. traction) battery current can be used as a surrogate measure of instantaneous energy consumption on the Prius. By observing the current into and out of the traction battery, it is possible to gain a better understanding of how the choices we make as drivers can affect energy consumption (energy which is ultimately generated from the burning of fossil fuels).

Here are my first observations which might be of some interest. Previously, for both the Gen2 and Gen3 models, the car’s computers (ECU) had some ‘intelligence’ to save energy when holding the car stationary in D (e.g., at traffic lights). After a fraction of a second of being stationary with the footbrake applied, the ‘creep’ action applied by the electric motor is switched off. The car no longer pulls against the footbrake. This is observed as a fall in the BTA value. As you lift your foot off the footbrake, the BTA value rises as current is applied to the electric motor and the car will creep forward.

On the Gen2, the trigger to switch off the creep and conserve battery power required firm pressure on the footbrake. It was possible to hold the car stationary with only light pressure on the footbrake and, without observing BTA, the driver would have no idea that the electric motor was continuing to pull against the footbrake.

This changed in the Gen3, where the amount pressure on the footbrake when stationary did not change the current draw. In other words, being stationary appeared in itself to be all that was needed to trigger a cut to the electric motor, so long as your foot remained on the footbrake.

My preliminary observations on BTA in the Gen4 appears to show a return to the Gen2 situation, where a firm pressure on the footbrake causes a fall of battery current draw that is greater than if holding the car stationary with only light pressure on the footbrake. The development in this Generation appears to be that this firm pressure allows the current consumption to fall to a level that is equivalent to being in P or N and also to a level lower than on the Gen3.

The initial BTA values for ‘creep’ appear the same as for the Gen2 or Gen3; but once the car starts moving, if there is no further input from the gas or brake pedal, the BTA value falls to maintain a slow crawl with hardly measurable current drain (0.4 A).

There is also a significant penalty in current drain if you hold the car stationary in D with the parking brake instead of the footbrake. The car’s electric motor will pull continuously against the parking brake.

The table below summarises my findings on the three generations. The conclusion is that you will conserve some battery power by pressing firmly on the footbrake when stationary; and if remaining in D, it is better to use the footbrake than the parking brake.

	Driver action​	Gen 2​	Gen 3​	Gen 4​
1	Stationary in D + light foot on brake	2 - 3 Amps​	1.4 A​	1.4 A​
2	Stationary in D + firm on brake	1.5 A​	1.4 A​	0.4 A​
3	Lift foot off brake in D (creeps forward)	2 - 3 A​	2.9 A​	2.9 A​
4	Stationary in N or P + foot on brake	1.5 A​	1.4 A​	0.4 A​
5	Stationary in N or P + foot off brake	0.9 - 1.1 A​	1.4 A​	0.4 A​
6	Switch on LED headlights​		add 0.5 A​	add 0.5 A​
7	Switch on interior fan at lowest level​		add 0.1 A​	add 0.5 A​
8	Switch on rear demister​			add 2 A​
9	Maximum EV acceleration (to mid-point of HSI)​			45 A​
10	Firm braking from 25 mph (40 kph)​			- 40 A​
11	ICE charging HV battery when at 2 bars (40% SOC) 1280 RPM​			- 5 to -12 A​

All tests were performed in Eco mode with devices switched off to start with (to achieve a basic reading) and then each act/device was actioned in turn. My Gen4 has Touch 2 with Go and this was left on as I had the MFD on the Gen2 and the similar display on the Gen3 activated for my earlier tests.


Note: Your ScanGauge II will need to have version 4.22 firmware. I am grateful to James at Linear Logic for his assistance. He can be contacted at [email protected] for any queries.

I will post results of other XGauges as soon as I am fairly confident of results. In the meantime, here is a link to a list of other XGauges:
» X-Gauge Categories » GENERATION IV PRIUS 2016+

 

Apologies in advance for Tapatalk users on mobile devices; the table will not display correctly. Works better using a web-browser.

 

All done on the flat. I'll post some hill start assist results in due course.

My impression is that an extra little push on the footbrake on the flat, like you do on a hill, seems to help trigger the low current state.

 

Thanks. Good to have corroboration from as many different methods as possible.

 

Found a quiet place to test out Hill Start Assist yesterday.

Seems like it is done with the friction brakes. I wonder if others can corroborate this?

BTA stays at the basic minimum level when you lift your foot off the brake after activating Hill Start Assist, and you don't see the added 2.5A for 'creep'. A few seconds later, the car will stop 'holding' and start rolling back (depending on the steepness of the incline). There is a faint sound which might be friction brakes releasing - not sure as it is a new car.

I hadn't realised the Gen4's control systems had control of the friction brakes. I had just assumed it would have been easier to program this control through the electric motor without adding servos to the system.

Then, having thought about it a bit more, I realised this Gen4 has DRCC (dynamic radar cruise control) which now works to a standstill. I have also read that the proximity sensors can also slam on brakes at low speed. Therefore, this car must have control of the friction brakes.

I admit I never checked it on my previous Gen3 as I have few situations in London where I would use Hill Start Assist.

It would be interesting to know if others have information from a Technical manual how this control system works.

 

I have not come across those values for the Gen 4 as yet but suspect there is continuing work taking place with LL in the background.

If I recall correctly, TPS was a popular option in the Gen 2 days in the search for the elusive 'sweet spot' of peak mileage. Not everyone was agreed with this concept.

Please may I ask if this was how you intend to use these metrics in the Gen4?