Getting A Second CANchecked MFD15 Gauge

TL;DR : not the best afternoon

Really happy with the MFD15 installed in October, it didn't take long to imagine a next step where the fuel gauge would also be replaced by a CAN one, and a final step that would see a custom base for my mobile phone holder take the space occupied by the coolant temperature dial.

Since the last failure of the oxygen sensor, I came to like having the lambda value displayed at all times. That also helped justify getting a second MFD15.

With all the discounts the end of year was likely to bring, I didn't rush the purchase. But as nothing came by mid-December, I placed an order from Sandtler24 before any hypothetical price increase in January.

First things first, I prepared an image for the boot screen. This time with the House of Speed and Quaife logos. The new device was powered from its USB port, the boot image loaded, the firmware upgraded to the latest version, the TRI file (CAN messages definitions) uploaded as well as a backup of the configuration from the first MFD15 to serve as a base. 

I kept all the display pages identical to the main unit, and did define page 7 to show two horizontal bars with the air-fuel ratio (lambda) and fuel level in liters. On page 8, a variant of page 2 with a vertical bar for fuel and lambda value plus battery voltage on the right. Finally, I did set the default display page to 7, so it shows up automatically at boot.

As CANchecked provide anti-glare films in the kit, I did install one on the new gauge in order to compare if it's better with or without one.

I did prepare a wiring loom that would repurpose the OBD connector I bought with the first kit and feed CAN both gauges as shown on the first picture. A CAN bus is just a pair of twisted wires, connecting all devices daisy-chained to one another. On longer networks, a ground wire is required too.

The original plan was to get rid of that chunky OBD connector and solder a small 2 pin connector from behind the OBD port of the car. 

I did extract the port rather easily once I understood there was a small tab to press on each short side, but it wouldn't have been possible to solder from behind as it's a crimped connector and not some sort of PCB. That's why I did reuse the connector from the OBD kit.

The small connector only provides power, it's connected to the original gauge's connector.

 

All went well except for a series of cascading small stuffs that didn't :

• The back of the OBD port broke when I pushed it back in place, it was really surprising.
• Installing the new gauge, I pulled on the wires that stole a power supply from the heated screen pilot lamp, disabling the fog lights relay I had to add previously. 
• Re-fitting those thin wires, the pilot bulb of the switch died on me. I was able to remove only the switch cover with universal pliers and a rag then a flat screwdriver from one side, and found that the easiest way to remove the bulb was to hold it still using miniature long nose pliers while rotating the switch around the steady bulb.
• The replacement bulbs were only found a few day later. They were hiding in plain sight, exactly where we thought they were.
• I've prepared and installed a proper 'Y' splitter loom with adequate spade connectors for the custom wiring.
• On the opposite side, I had a bogus solder joint on the wiring between the OBD plug and the main length of CAN wiring.
• I had first to identify if it was a software issue (by only connecting a single gauge, enabling the bus termination in the gauge...) or it is was hardware (playing with the cables).
• As the loom was a tad too long, I did shorten it by about 20cm while I was working on it. 
• Threading the revised loom through the dashboard, I did disconnect a pin of the shift light. 
• To reconnect the shift light, I had to remove and re-install the tachometer.

All is fine now. The pair of displays work as intended and the hacky wiring for the fog light relay and dash-cam power supply has been improved greatly.

The result looks great, the shift light "bubbles" and light are synced together, and so are the pop-up alerts I've defined for when coolant is too hot or oil pressure is too low.

Next time, I will use the provided CAD model as the base for a custom 3D-printed phone holder.
Looking at the last picture (below), it would replace the long arm and the suction cup and have the short arm with the ball joint attached directly to the mock gauge. Some black acrylic glass would look nice. I would also route the USB power lead through it, probably with some brush thing or between two piece of black foam. I could as well include a press button to dim both the MFD15 together and get their left button free to move left in the pages.