2005 Mazda3 2.3 Multiple Codes

salguod

Mr. T'bird
My 2005 Mazda 3, 2.3, 5 speed, 175K miles is throwing multiple codes. From Torque:

Current Faults:
  • P0128
  • P0138
  • P2195

Pending Faults:
  • P0126
  • P0455
  • P2187

Torque also lists all those codes again plus P2503.

The car generally drives well, but occasionally has a fluctuating idle (sometimes requiring the throttle to keep it running) and is sometimes hard to start to the point of requiring pressing or pumping the accelerator. Mostly, however, it runs well.

I'm assuming I have multiple issues here.

The 0128 / 0126 seems to indicate a thermostat.

0138 / 2195 / 2187 might point to an O2 sensor, but I'm finding conflicting info.

I have also had recent issues with multiple odd electrical symptoms. Things like using the turn signal causing the radio to turn off and a loss of power steering. These would reset after the car was restarted. I cleaned the chassis ground near the battery which fixed that. I mention it because of the 2503 (charging system voltage low) and I wonder if I've got a dirty engine ground contributing to some of these problems.

My thought now is to start with the thermostat and then move to the B1S1 O2 sensor.

Any other ideas?
 
What coolant temps are you seeing? A stuck-open thermostat can cause drivability issues, so your plan to change it is sound.

Also, a faulty/intermittent battery can cause weird electrical issues. You might want to have yours tested.
 
I didn't check the actual coolant temps, so I'm not sure. Thermostat should go in tonight, if all goes well.

Battery was replaced in January, it should still be good. I'm not sure what the difference is in the way that Torque displays the codes. The battery voltage code was down at the bottom of the list and not tagged as either "current" or "pending".
 
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