I just bought an 85 Firebird with the 2.5 engine and TBI. The check engine light came on, and showed code 13, so I replaced the oxygen sensor in the hope that it was just a bad sensor. Unfortunately that did not fix the issue. So I checked the voltage at the ECM for the oxygen sensor and its ground, and it is only reason .18 bolts when it is supposed to be around .45 volts when in an open loop. The engine never goes to a closed loop, so that voltage is not changing at all. Do you guys think that my ECM is bad, or that there is just a short in the wire going to the oxygen sensor, or maybe just a bad connector at the oxygen sensor?

 

You should refer to a gm fsm or google your service number of the ecm to see if you can find a schematic. It should be a purple wire at the ecm. In cl if the o2 mv are toggling at the ecm pin for the o2 the ecm would be faulty.