Hello all,
Irecently stumbled back into a P0138 code (dealing with post Cat o2 sensor). About 2 1/2 weeks ago, I replaced this sensor and everything ran normally. Now after today, its back! Its around mid 70'2 here and I towed my camper around 150 miles back home and the light came on about 2 miles from the house. I noticed when we were passing through a couple small town near home, stoplights especially, it seemed to idle and shake erractically when stopped. I have since been home under the truck ('01 1500 4X4 QC w/ 145,000 mi.) looked at the new connector. Seemed alright checked the wiring for any shorts, heat etc. Looked at the pre-Cat sensor (which I plan on replacing since I did the other one) and it looks "used" but wiring still intact. Could my Cat be worn out, needing replaced or am I barking up the wrong tree. I know similar situations have been resolved in the past but I am looking for any fresh ideas. Thanks a ton to all who respond.

Chad

 

No one knows anything about this?? I just replaced the pre-Cat sensor and took it out for a spin. Light is on, and its still shakes a little. Any help would be GREATLY appreciated.

Thanks,
Chad

 

I have similar issue. My cat rattles really bad. Your cat might be bad.

 

ihave the same issue. I think my cat is starting to go bad. i plan on fixing that as soon as i have time. havn't been driving the truck to much since the gas prices cant figure out which way they should be going [:'(], so it hasn't really bothered me.

 

I had this issue and it was indeed a bad CAT. Also started throwing cylinder misfire codes before the CAT went out. Did plugs, wires, cap, and rotor button. Take it to Midas and they will do a free check of your exhaust. They wanted $1500 to fix it. Paid $300 for parts and a few hours of my own time in the driveway. Also, check for the dreaded plenum pan oil leak. If your blowing oil thru the pistons it will definetely mess up those O2 sensors.