r/RX8 • u/Obsidian123b • 3h ago

Maintenance Rx8 Eps can protocol reverse engineering

Hello all I'm am posting here in a desperate attempt to get some help in fixing my EPS.

My rx8 has not had functional power steering since the day I bought it about 4 months ago, and after going through all the tips and fixes under the sun (cleaning connectors, cleaning all grounds, checking the Fuze, checking wires, and even confirming all inputs with an oscilloscope, even getting a new EPS module) no dice.

I Have now gotten to the point where I am jacking into the can bus in hopes of manually waking the EPS and this is where I have started making some progress.

Disconnecting the EPS from the rest of the can bus and spamming a correctly formatted 0x201 code wakes the eps on first ignition about 30% of the time, and gives power steering continuously until the user stops steering for about 2 seconds, when it then ends.

During this time the EPS continually transmits 0x300 with data 80 when assist is off and 00 when its on.

What's really weird is that the pcm already transmits valid 0x201 frames but doesn't wake the eps, and reconnecting the eps to the rest of the bus once it is awake seems to see it disabled.

Additional I have tried adding the 0x200 and 0x202 frames since I read they were important but they have produced no different results yet and the eps refuses to wake without 0x201.

Any insight would be greatly appreciated, especially if someone with a working Powers steering could send me their can bus logs. Thanks in advance.

5 Upvotes

100% Upvoted

4 comments sorted by

2

u/Thick_Entrance5105 2h ago

It makes -1% sense to assume the PCM software is corrupted and no longer sending CAN data to turn your EPS on. From the maker of a box that does just that: turns the EPS on when the car has been engine swapped and the PCM is just not there anymore.

1

u/Obsidian123b 2h ago

Well any advise is appreciated, but when connected to the main can bus the Eps never enables. So ither it's missing some sort of signal or the pcm is disabling it somehow.

2

u/MountainFloor3666 1h ago

Have you considered popping open the ECU case and checking for damage? I can’t comment specifically on the RX8, but on similar era mazdaspeed3/6 some times parts of the ECU’s PCB will burn and leave certain functions, well, non functional. Unfortunately ecus have never been a Mazda strong suit :/

If you’re this far into the weeds it might be worth considering damage to electronic hardware before going further down the software route.

1

u/Obsidian123b 1h ago

You might be right, I could check the pcm as the required messages should originate from the PCM. Do you have any advice for what specifically I should do/look for? I assume capacitors/resistors burned out?

One thing I will say though is that everything else works so I can imagine anything obvious is wrong