Mazda Tribute, all 4 02 heater circuit failure, etc

I have a 2005 Mazda Tribute, 3.0. Truck went from running perfect to CEL and 6 codes. p0135 p0141 p0155 p0161 ( heated o2 circuit failure ) p0403 (egr solenoid circuit failure)
p0443 ( purge valve circuit failure )

I changed the egr vacuum solenoid, since it is a part known to fail. All the parts did not go bad in one shot. I removed the purge valve solenoid, it clicks and allows air passage when energised.
It seemingly is working as it should. I should of taken an ohms reading on it, but I assumed since it clicked and allowed air passage it was ok. No air could pass without it being energised.

All 4 o2 heater circuits and the purge valve solenoid share the same fuse. I have checked the fuse and replaced it anyway. I have 12 volt power going to the purge valve, and power going to pcm from purge valve.
It is PCM ground side switched. I have 12 volts going to egr vacuum solenoid as well, and 12 volts going to PCM. I also road tested with a vacuum gauge and had vacuum to egr with engine warm and throttle applied.

I unplugged all 4 o2 sockets and checked for bent pins or corrosion. I sprayed some eletrical contact spray, but they all looked just fine. The 02 heater circuit is supplied via a splice to all 4 sensors.
I checked the return back to the pcm on all 4 o2 sensors and all had 12 volts. Am I correct that is normal, and the pcm should ground them and complete circuit?

I have current going too PCM from all the parts the codes point to. I cleaned grounds by battery, and I cleaned PCM ground to firewall. Is the PCM the issue here?

These are all failed circuit codes, they have a common power wire ( accept egr solenoid ) and they use different grounds. How could the purge or egr circuits affect the o2 heater circuit?
I could see any bad emmisions part cause lean or rich conditions, but circuit failurs?

I am at a loss here.

The EGRVR solenoid does share a common power feed with all those other components.

When car is running maybe there's a voltage drop occurring to high resistance somewhere on that leg.

Are all six of these hard faults, or do the come back intermittently? It could be that you're looking at a poor connection at fuse #5, or high resistance between fuse #5 and the PCM Power Relay. Wire gets shaken or bent the right way, the voltage drops out, and you get codes.

It was intermittent at first but now pretty much right away. I had the PCM replaced last year for the well known plugs and coils burning out the PCM. They have agreed to take it back and have a look. I hope they find burnt out ground circuit and send me a new one or repaired. If the PCM checks ok, I will need some help figuring out where and why there is a voltage drop. I get 12 volts to the pcm from all failed components, seems the ground side switching is defective, but not sure if that would be intermittent. Should have an answer Monday or Tuesday at the latest. I will keep this thread updated.

thanks, this is a great diagram. I have one but it was broken up in many pages.

it was the PCM, all fixed now

karlN wrote: it was the PCM, all fixed now

Interesting. :ohmy: This is one of those times I'd love to know the internal construction of the PCM, 'cause it sure seems like all those circuits have something in common.

Thanks for the update!