2015 XC70 P0420 with CAT pics, troubleshooting assist

[Cmobile]

I noticed my idiot temp gage on the dash hits normal temp at 149°f. At idle I slowly brought up the RPMs to 4700 until OBD2 showed 212° F. The idiot dash gauge didn't budge from centerline. Not uncommon.

However, my ride to work this morning at an ambient temps of 32°F, my OBD showed temps at 178°f to 182°f on the highway, 65mph and 20 minutes of driving. Downshift a gear and temps went to 188°. The dashboard temp gauge of course was normal centerline

Idling the temps are 184 right now with ambient temps of about 70°.

 

[Dr_Dr3i]

EVAP codes wouldn't have anything to do with a bad gas cap, perhaps, would they?

 

[WobblyElvis]

Fully warmed engine at steady idle, MAF reading jumping from 3.0 to 4.0 does not seem right to me. Should sit close to 3.0. I ain't no expert. Maybe someone here knows if this acceptable but my cars don't do that.

 

[Cmobile]

Fully warmed engine at steady idle, MAF reading jumping from 3.0 to 4.0 does not seem right to me. Should sit close to 3.0. I ain't no expert. Maybe someone here knows if this acceptable but my cars don't do that.

Good point. I recently found a vac leak that has been corrected since the scan pics were taken.

Will be ordering a new T-stat/temp sensor combo kit. May not be related to the P0420, but sweedspeed and other Volvo sites highly recommend changing T-Stat/CTS combo unit between 100-150k miles. Volvos of this vintage have a unique thermostat design.

 

[Cmobile]

I installed the new downstream O2 sensor. Its been about 300 miles since, and the voltage in the downstream O2 is relatively stable, for the first time since i started tracking this issue. No stored or pending codes.

New coils, plugs, thermostat and hose on order from FCP.

No noticeable oil consumption, currently running M1 0w-40 FS and 2 bottles od rislone engine treatment. The sump holds 8 qts, so not really double dosing.

This likely would have been resolved by simply replacing O2, but glad I went through the cat cleaning process before changing the sensor. Along with inspecting everything, testing, cleaning, etc.