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CAN Bus Communications Decoded: Step 1: Plan Your Network

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Step 1: Plan Your Network


00:00 - We've got quite an interesting worked example to go through in the High Performance Academy SR86 racecar here.
00:08 So this is a racecar set up for endurance racing and it's fitted with an SR20VET engine which actually makes quite a lot of power, it's a pretty impressive piece of kit.
00:18 And being the data nerds that we are, it is fitted with every sensor under the sun because as the saying goes, without data, all you've really got is an opinion.
00:28 So we've got a lot of sensors in this vehicle and configuring everything to communicate nicely can sometimes be, you have to be a little bit creative about these things and that's exactly the situation that we're finding ourselves in now.
00:40 What we're trying to do is get the per cylinder wideband O2 sensor readings to have exhaust back pressure compensation on them.
00:51 So just to unpack that a little bit.
00:53 We've got an individual wideband sensor in each of the runners pre turbo in this vehicle, so that means they are going to be exposed to exhaust pressure when the engine is high in the RPM range and under quite a lot of load and that turbo's really working quite hard.
01:08 As you apply pressure to the measurement element of wideband O2 sensors, you do actually find that their reading gets skewed.
01:17 Now the Link CAN lambda controllers that we've got in this, and there are 4 of them that controlling and reading the output from those sensors can actually compensate for this but to do that they need valid data on what the current exhaust back pressure measurement is.
01:32 So we've fitted a 0-100 psi absolute sensor to the exhaust manifold, that's being read by our MoTeC M150 ECU that's controlling most of the rest of the electronics in the vehicle.
01:47 Now in the MoTeC M150s the default CAN transmission templates are actually reasonably locked down and there's not one that you can choose in there that will natively communicate that exhaust pressure to our Link CAN lambdas.
02:00 So this is where we find ourselves in the situation that we're going to need to use another device to act as a gateway and this is definitely something that you find yourself, a situation you find yourself in quite often.
02:12 So we're going to use our MoTeC C125 display because that's really nice and relatively easily configurable to be able to read the data reliably from our M150 and then convert it and transmit it out in such a way that our Link CAN lambdas are going to be able to read it.
02:31 So going back to our HPA 5 step process, first step of this process is going to be to plan our network.
02:38 Now little bit tricky to do in a racecar like this that's actually already built and already wired.
02:44 All of that has been done before but what I do have access to is the documentation for the vehicle and that lets me know that our M150, our Link CAN lambdas and our C125 are actually all on the same bus and that bus is running at a speed of 1 Mb.
02:59 Now it would be lovely if the M150 could talk directly to those CAN lambdas but it's not a situation that we can easily achieve.
03:05 Would be possible to do it with M1 build but we're not going to go down that route at the moment.
03:11 But I know that I'm going to be able to get our C125 reading that data and spitting it out.

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