My '03 suburban threw a P0135 code recently. Being lazy, I purchased a new O2 sensor without troubleshooting the problem to confirm. After installing the new sensor and not fixing the issue, I started to troubleshoot, here's what I found and where I'm at now....need some help.

• Scanning with HPT, I noticed that B1S1 O2 doesn't warm up (increase voltage) during startup like its brother B2S1. B2S1 increases voltage from ~0.450mV to 0.9 mV during startup. B1S1 stays at 0.450 mV during this time.
  
• I verified 12VDC power and ground from the battery.
• I'm getting 0.450mV from the PCM, but only when I connect to battery or chassis ground. This leads me to believe that the ground wire back to the PCM is open
• I tried connecting the PCM ground with the battery ground (at the O2 wire harness) but this doesn't improve things.

Aside from tracing the ground wire from the harness back to the PCM, any suggestions on how to fix this? BTW, no other codes are present, so I'm not thinking there is a common ground (at the PCM) issue, or I'd see other codes/malfunctions.

Thoughts?

 

Where did you get the sensor from?

What brand is it?

 

The new O2 is Bosch. To eliminate a bad sensor being the problem, I switched the D side sensor to the P side and vice versa. The problem stayed on the D side and did not follow the sensor.