2010 Mazda6 2.5 no communication with scan tool and no start

No start with no com. with scan tool. checked all powers and grounds to the PCM. MAF has 5v reference with key on. Dash lights up with all lights including security, cel, abs and bunch of others.

Main engine relay is not engaging, I can apply voltage manually and can hear fuel pump kick on and throttle body engaging. What should I do next?

I'll take a crack at it. I've only got a short time to hop in and answer questions though so someone else might have to pick it up where I left off. I'll try to check back in tomorrow though if I can

First, let's have a peek at what we're looking at power-wise



Start basic. I'd check PCM Fuse 10 Amp as well as Engine Fuse 10 Amp. Looks like the main relay provides power to both. See if you got power on one and not the other with the key on to start. That'll at least verify the integrity of the main relay, if nothing else. Also, I'd see if you can pull the relay and verify that the one terminal is getting power at all times.

I can't really find a picture of it but I imagine that the main relay is getting it's power from a cable that comes from the battery. Typically, these guys are bolted. There's usually a cable that has an electrical eyelet that slides over the bolt and is secured with a nut.

Personally, if you have no power at those two fuses, I'd start with verifying your positive cable at the battery is actually tight. They can sometimes look great and not be so. You might have to pop the main panel under the hood to verify power is going where it should.

Good luck!

I've already verified powers and grounds at the pcm.

tchaudhry10 wrote: Main engine relay is not engaging, I can apply voltage manually and can hear fuel pump kick on and throttle body engaging. What should I do next?

Apply voltage where? To the PCM fuse that's powered by the Main Relay?

If the Main Relay has power on the control side, but no ground on the black/blue wire from the PCM, then I'd verify that wire is good all the way to the PCM.

Just for giggles, what's the HS-CAN network resistance between pins 6 and 14 at the DLC? I don't know that a network problem would cause a lack of Main relay engagement? But it's just another good check before pulling the trigger on a PCM. Can you communicate with any other modules on the HS-CAN network?