Hey guys!
I'm having issues with my rx8. Here's a small description of it:

Before I start describing it, this issues happened intermittently before, but it's permanent now.
So my rx8 doesn't want to start nor crank and the immobilizers of my car flashes Here are the codes I got when trying to fix the car with my OBD-2 scanner:

U0100 Lost Communication With ECM/PCM "A" (Connection error between TCM and PCM)
U0073 Control Module Communication Bus "A" Off. (One or more modules is not able to communicate properly over CAN bus 'A')

From the workshop manual and some threads I've read here, I got a code from the immobilizer system flash. Here it is:

∩__∩∩∩∩∩∩____ = Communication error between the keyless control module and the PCM (no response or mismatched conditions)

As you guys can see, 2/3 of the problems are pointing at the PCM. I don't know if it's wrong, since this problem happens intermittently. That's why I'm sure my PCM is not fried.

What do you guys think that could be the problem?

 

The keyless entry module is on the passenger side, I haven't looked at that module in a while, but I suppose a passenger could have hit a part of the wiring. Somehow the wiring or module got damaged and vibration from driving could have caused the intermittent symptoms before losing connection entirely. Does your key fob work?

When you try to start the car the immobilizer + ECU + keyless entry module must be connected via CAN to be happy. I am unsure if buying a new module will just connect, you may need a dealer or a locksmith to allow the units to talk to each other. I suggest being sure that the wiring is correct first, disconnect and reconnect the Immobilizer+ECU+KeylessModule.

I believe racingbeat offers an immobilizer disable ECU reflash that may bypass your issue, but again I suggest trying to find the problem first.

 

Thanks a lot for the reply!

From what I understand, my key fob does work since I can lock/unlock the door and turn the car to ignition. But I can't start it. Also, I did take it to the dealer and they told me I needed a new key. So I did make a new key and the problem stopped for a couple of days, then it came back. I contacted the dealer and they got mad at me. So now I'm avoiding going to them haha.

Anyways, I'll take a look into the wiring, but my maim concern is if it's PCM that's not giving power to my keyless module and my TCM.

 

The dealer got mad at YOU!?

That's f-d up customer service.

 

Yep haha. I don't trust garage and dealers anymore because of that and another incidence. When I bought the car (a few months ago) the previous owner lied to me about the cars condition. Just to be sure that he was lying or not, I sent it to a garage to get it inspected and compression tested, but it turned out the garage was friends with the previous owner. So all the report I got was false and now I'm stuck with a rx8 that has bunch of electrical issues

My car drove for 2-3 days, but then stopped working. Took it to Mazda and they told me I need a new key and forced me to do a compression test which turned out that it's even a miracle for the engine to even be running.

Yeah I got scammed. This is my last attempt on fixing it before I sell it and get rid of it

 

Update on my problem:
I noticed that my car starts when it's hot outside.
The codes also disappeared.
What do you guys think could be the problem?

 

You could have corroded or varmint chewed wiring.

Inspect your grounds.
Be sure your battery terminals are clean and tight.
Nuts can be tightened all the way on those strap types and the terminal can be stretched out and loose.

 

I'm planning on inspecting ground. Hopefully that's the problem. Or else, I think I'm gonna take a heat gun and slowly test in which area the heat makes the circuit start working. I don't know if it's gonna work, but doesn't hurt to try.


Hopefully I figure out what's the issue

 

Have you found out the issue?

 

Hey!

I'm planning on tackling the problem in a week (during vacation), so no progress has been done on it yet!

I will say, since I'm stored the car for winter (2-3 weeks ago), the car detects the key every time I go check for fun. I don't know if this does much, but I think this makes the case of a faulty ECU less likely to happen. So my guess is that it's bad ground.

Anyways, once I figure out the issue, I wouldn't mind posting here the fix I did.

 

Hey guys!

I just wanna add a small update on what's going on. After inspecting wires, I found a ground wire close to the PCM that's pretty much uncrimped in the end really badly. I will crimp it and hopefully this fix the issues I have.

For those with basic electrical knowledge wondering how this can be the issue, here's what I think (correct me if I'm wrong). Since the wire is kinda uncrimped, the diameter of the end of the ground wire is smaller, which makes the resistance value of the wire go up. If we add up the temperature rising because of the heat of the engine (the wire is located in the engine bay), the resistance goes up as the temperature rises. The more the resistance rise, the harder it is for the current to flow. So, I think that the intermittent problem can be caused by this ground wire and possibly many others on the car with similar conditions.

I really hope this is the cause of the problems I'm having.

What do y'all think?

 

Did you resolve the issue?

 

Nope. I'm still trying to. I did make quite a lot of progress. I'll post a update if you guys want if I actually manage to fix the issue.
​​​​