Originally Posted by
Yellow05C6
Sorry about the length, I’ve tried to be concise. We are having trouble with LS1B ECMs and their O2s. We’ve built wiring harnesses for both 1M and 0.5M LS1Bs w/o issue. Suddenly the last two harnesses (both for 0.5M LS1Bs) result in the ECM not being able to “see” HO2S11 & HO2S21 sensors (i.e. O2 voltage remains a steady 450mV after the O2 heats up). I cannot say if the ECM would respond with LTFT/STFT because I have no scan data for an engine running in closed loop. We checked pin-to-pin in both harnesses and found no errors and they are duplicates of past good harnesses. First we attached a 1M LS1B to a “bad” harness. The 1M LS1B did “see” the O2 sensors (i.e. O2 voltage drops to small mV range with the sensor in air). We reinstalled the 0.5M LS1B into the “bad” harness and re-verified that the ECM could not “see” the O2. We tried several 0.5M LS1Bs all with the same 450 mV result. Then we back probed one of the O2s and found sensor voltage to actually be 90mV and descending even though the scan still indicates 450 mV. Stated plainly, the 0.5M LS1B is acting like the O2 sensor is not connected. In all cases we are directly applying 12 volts and ground to the O2 sensor heater (as we have done in the past), and O2 sensor temp hovers around 200F. Also the engine is not running but the O2s are in air or in a cold exhaust pipe. All other sensors are installed and read correctly. We’ve even injected simulated CKP & CMP signals to fool the ECM into thinking the engine is running. A Snap-On Scanner also displays a continuous O2 reading of 450 mV. This problem appears to have started after V7.5.7 Build 283 and V8.2.2 Build 276 were installed. Harnesses & ECMs built / programmed before the May release do not exhibit this problem. I’m not sure what the previous versions were; but it had probably been more than a year since the previous update. 1.0M, 0.5M LS1B tune and scan files as well as the ECM pin-outs we use are available if they would be of interest.