So I had been dealing with this problem for almost a year now with no solution. I Get a CEL code p0038 no matter what. I had Agency power full exhaust and that’s what originally gave me the cell, recently I have taken the mid pipe off but left the exhaust on.
I reset the ecu (pcm) all 3 ways that are possible
Changed out the o2 sensor 2 times
Measured the voltage between the ecu and o2 sensor.
Cleaned out all the connectors.
Checked all the wiring for any lose wires or shorts.


I am thinking that my ecu has failed!?
Mazda Dealer Has no Clue!

I also get that ABS, traction and break light lights that will kick on from time to time from staggered tires.
And get the Coolant sensor failure red light.

Any Help with this will be awesome because at this point I am out of ideas

 

Pinched wire harness.

 

Pinched wire harness makes the most sense but I used a multimeter and test all the voltages on both ends (on the o2 side and the PCM side) and I am getting stable voltage on all wires.

I also have a COBB access port and been building custom maps for myself and I can turn off the code but that does not help me pass inspection. On inspection machine I just get status not ready on the heater.


P.S. I love you MazdaManiac I have learned a lot from you. .

 

If you turn off the code and then leave the PCM alone for a week, it will set the readiness flags and pass emissions.

Did you test the impedance of the heater circuit? That is what is throwing your code, not the output signal to the PCM.

 

I turned off the code before and drove it for a week before and it still showed on the inspection machine, I will try this again and drive for 2 weeks or more this time.

I did test for impedance in the heater and I was getting the correct ohms on ignition but then it would drop to 0. Now I know that heater should stay on all the time and it test during pcm cycles.
The cell wouldn't kick on right away after reset but 5 min or so after. (Didn't matter if I was driving or not)

This is what led me to think it was the PCM and not a circuit issue. I can recheck this weekend.

Any suggestions on how to test this correctly.
I’ll make sure to take pictures and post it on the DIY just in case someone has this issue.

Thax

 

Tested everything and impedance of the heater circuit is ok.

 

Which O2 sensor did you change?

 

Rear, the one that connects to the Cat.