Pontiac Repair: 2001 Montana P0135 code, coolant temp, pontiac montana

Question
I have a 2001 Pontiac Montana.  It registered a P0135 code.  I re-set the computer and the code returned the next time I drove the van.  I replaced the O2 sensor and visually checked the wiring leading to it for any damage (there was no obvious damage).  I reset the computer and it still is registering a P0135 code.  I can drive the van to get it fully warmed up, and drive at highway speeds and every thing seems fine.  It then sets the code after I have driven several miles at moderate speed (30-45 mph) and I am driving slowly at low throttle or with my foot completely off the gas while coasting downhill.  What is the next thing to check/replace? Any other info you can offer?

Here is the Freeze Frame info from the scan tool;

Trouble code P0135
Fuel SYS1
  CL, using HO2S
Fuel SYS2
  N/A
Calc Load (%)
  4.7
Coolant Temp
  180 F
ST FTRM1 (%)
  1.5
LT FTRM1 (%)
  10.1
MAP (in.hg)
  10.0
Engine RPM
  1203
Speed (mph)
  24
MAF (lb/min)
  0.874
ABSLT TPS (%)
  0.0
  

Thanks for your help, Mark  

Answer
Hi
P0135 is the heater circuit.
You should check for B+ on the pink wire going to the sensor.
Check and make sure you have ground on the black/white wire.
If you have B+ on pink, and (-) on the blk/whi, I would HIGHLY suspect a faulty sensor. It is WAY more common than one may think.
If these items DO NOT check out, make sure the IGN1 fuse is good.
If all this checks out, you MAY have a faulty PCM.
I Hope this helps
PAwl