Po155
 

Hi. I'm new to this forum. I'm showing a PO155 code on my 2003 S-10, 4.3, 2wd. I'm planning on changing it tomorrow and a friend suggested to change both of the sensors that are upstream. Anyone have any experience on this? Aside from this code, my truck looks and runs as it did when I bought it new. It now has just a tad over 162,000 miles on it.

Welcome to the forum.:) P0155 is bank 2 sensor 1, i.e., the one on the passenger side, between the exhaust manifold and the catalytic converter. The problem is either the heating element inside the sensor or the wiring. Take the electrical connector off, find which electrode on the connector (engine side) has ignition voltage with key on, engine off. Then, take a look at the the other connector (sensor side), find the mating terminal electrode, and then measure the resistance across that electrode and the one next to it in that half of the connector. If the resistance is high (> 6Ω), replace the sensor.

As far as replacing the sensor, you'll need a special O2 sensor socket, maybe a torque wrench, and, if it's seized on, some penetrating chemicals like PB Blaster. Don't drop the new sensor or bang it against a hard surface and be sure to coat the threads with some anti-seize compound if it came bare and torque to 30 ft-lb.