Hi, I'm a newbie, bought a 2002 honda civic ex 4dr for my daughter. 180,000 mion cluster, but was told had a rebuilt engine with about 55,000 mi. Car ran well for 2 days, then noticed that the temp gauge started to rise very high when stopped or going uphill, then fell again when I started to moving faster. The seller told me the car sat for 4 months so he said it mat be the thermostat and replaced it. The car still overheats when stressed and now the check engine light is on. I plugged in a code reader and got a P0420 code, cataytic converter. Are these two issues related? Any suggestions on a fix? Thanks, my daughter forbidden to drive the car until i fix this.