Adding data display to Bolt EV with UltraGauge MX

UltraGauge MX (bottom center) shows various info next to the iOS 14 CarPlay screen (right)

To keep a detailed log of the Bolt EV's battery status, I've been using a Bluetooth OBD-II adapter that connects to a smartphone for the past two years. While it worked well, I wanted to have a permanent display showing the data and installing an iPhone to do so seemed to be an overkill. So I searched for dedicated "gauge" units that allowed for customization and narrowed the selection down to ScanGauge 2 and UltraGauge MX. The former allowed for more custom data (25 PIDs vs. 8), while the latter had a bigger screen (8 lines vs. 2). I ended up with the bigger screen.

With the device at hand, I had to find a way to program it to display Bolt EV-specific data using the existing custom PID information, and then install it on a place where it is both easily visible and properly shaded. After a bit of work, I was able to fulfill all of the objectives, as you can see in the photo above. The first page shows the actual vehicle speed, accelerator pedal position, various battery information including State of Charge (both raw and displayed), usable capacity, and temperature, as well as current trip distance and 12V battery voltage. Let's see how this was done.
First boot-up of UltraGauge MX

Initially, UltraGauge detects how many of the 60 standard OBD-II PIDs (Parameter Identifications) and 28 self-calculated data it supports are available on the car. Because Bolt EV does not have an internal combustion engine, most of these are irrelevant and unsurprisingly unsupported. Of the 20 said to be usable as shown here, only 7 of them are standard PIDs and none are related to monitoring the high-voltage propulsion battery.
PID # Description Unit
010D Vehicle speed km/h
0121 Distance driven with CEL (Check Engine Light) on km
0130 Warm-ups since TC (Trouble Code) was cleared Count
0131 Distance driven since TC was cleared km
0142 ECM (Engine Control Module) 12V Battery Voltage V
0146 Ambient Air Temperature °C
0149 Accelerator Pedal Position 1 %
So I had to devote all of the eight custom PID slots available for this purpose. The problem is that the screen for configuring them (MENU - Gauge/Page Menu - Select Gauge/Page - M Gauge Setup) looks like this:
MGauge programming screen for slot 1

And it's not easy to make sense of it at first. I needed to translate the information found in an unofficial list of custom PIDs for Bolt EV into this format. After reading the UltraGauge MX programming supplement and researching the CAN Bus protocol, I was able to do just that. For these PIDs...
PID # Description Unit Formula
228334 State of Charge (Displayed) % A × 100 / 255 + 0
015B State of Charge (Raw) % A × 100 / 255 + 0
2241A3 Battery Capacity (for 2017-18 Bolt) kWh A × 999 / 31250 + 0
22434F Battery Temperature °C A × 1 / 1 - 40
22436B HV Charger Voltage V A × 1 / 2 + 0
22436C HV Charger Current A A × 1 / 20 + 0
22437D Last Charge Amount kWh A × 1 / 100 + 0
2241B6 Battery Heater Power kW A × 1 / 1000 + 0
I programmed UltraGauge like this:
# Abbr1 Abbr2 TData TCtrl RCtrl RPos Mtch X / + Out Ave L/R
1 SoC D % 07E4228334 93 31 2008 628334 0064 00FF 0000 00 00 32
2 SoC R % 07E0015B 92 21 1808 415B 0064 00FF 0000 00 00 32
3 Cap kWh 07E42241A3 93 31 2010 6241A3 03E7 7A12 0000 00 00 22
4 Bat °C 07E422434F 93 31 2008 62434F 0001 0001 FFD8 00 00 30
5 Chg hvV 07E422436B 93 31 2010 62436B 0001 0002 0000 00 00 32
6 Chg hvA 07E422436C 93 31 2010 62436C 0001 0014 0000 00 00 32
7 Chg kWh 07E422437D 93 31 2010 62437D 0001 0064 0000 00 00 22
8 BHt kW 07E42241B6 93 31 2010 6241B6 0001 03E8 0000 00 00 13
You can see that TData is composed of the header and the PID. The header specifies which ECM the data should be coming from and there are at least eight of them (E0 to E7) on Bolt. The numbers used in the formula are entered in hexadecimal, as with other inputs. After making sure that the programmed PIDs were working as intended, I went ahead with the permanent installation of the device.
First confirmation of all eight custom PIDs working on UltraGauge MX
UltraGauge MX and two of its mounts - horizontal (top right) and hook-and-loop (bottom right)

Even knowing the approximate dimensions, it was a bit difficult to get a good idea of where the UltraGauge should be installed. So I ordered it with both the horizontal mount and the hook-and-loop mount to give myself some options.

UltraGauge horizontal mount is attached under the Power button

After trying various positions, I settled with the spot just below the power button. There, I could see the screen through the steering wheel most of the time, and the device would be largely shaded from the sunlight.

Cable is attached to the OBD-II port (bottom left), then routed under the steering wheel towards the right

As a bonus, the cable is naturally obscured for the most part and uninstalling in the future will not be a hassle. The hook-and-loop mount was the only thing left over.

Page 1 is for driving (top) and page 2 shows charging information (bottom)

With the installation complete, I fiddled with the page configuration to suit my needs. With several days of testing, the first page now contains the information I wanted to see while driving, and the second page shows real-time charging data.

The second page complements the dashboard with more detailed information during a charging session

This is how it looks like when the car is hooked up to a DC fast charger. One feature I miss from the smartphone-based solution is that the charging power (= Voltage × Current) isn't automatically calculated and shown because UltraGauge does not support adding or multiplying PIDs together. But other than that, I'm pretty satisfied with the new solution.

Changing power off detection method

Before wrapping up, I should note that the automatic power on / off feature of the device (MENU - UltraGauge Setup - Compatibility - Pwr off (on) Detect Mode) needs to be tweaked in order for them to work to a reasonable degree. UltraGauge provides six modes of detecting the car powering off, but none of the first five work. Modes 0 and 1 don't detect any changes, while Modes 2 to 4 always think the car is powered off.

The last resort that uses the 12V power's voltage level - Mode 5 - has to be selected. But determining the cut-off voltage (MENU - UltraGauge Setup - Compatibility - Bat Low Threshold) was a bit complicated. The default was 12.85V, but this kept turning the screen off because the level fluctuates between about 12.3V to 15.1V while driving my Bolt. On the other hand, setting it to 12.30V would not immediately turn the screen off. The current setting is 12.45V, which has reliably kept the screen on while driving, and turn it off within a few minutes of actually powering the car off.

The side effect of using Mode 5 for the power off detection is that the power on detection is forced to Mode 2. This relies on the 12V power's voltage level as well, and the screen itself has to be manually turned on by pressing the UP button behind the device after powering the car on. This wasn't as big as an issue as I initially thought, because I get to turn on the screen only when I need to.
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