Correct sensor?
P0136: 02 Sensor Circuit Malfunction (Bank I Sensor 2)
Bank 1, Sensor 2 is on the passenger side and aft of the catalytic converter. Since you are not getting P0141: 02 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2), the PCM is recognizing the presence of the sensor but the O2 level voltage reported is not as expected.
According to the MY 1998 OBD System Operation Summary:
"A functional test of the rear HO2S sensors is done during normal vehicle operation. The peak rich and lean voltages are continuously monitored. Voltages that exceed the calibratable rich and lean thresholds indicate a functional sensor. If the voltages have not exceeded the thresholds after a long period of vehicle operation, the air/fuel ratio may be forced rich or lean in an attempt to get the rear sensor to switch. This situation normally occurs only with a green catalyst (< 500 miles). If the sensor does not exceed the rich and lean peak thresholds, a malfunction is indicated."
P0136 is reported when Bank 1 Sensor 2 fails to pass the above tests.
Since you get the same results when the Bank 2 Sensor 2 is connected, I suspect there must be an electrical problem between the sensor connector and the PCM. You might try disconnecting and then reconnecting the PCM connector. That will clean the contacts a little. Make sure the PCM connector retaining bolt is snug but do not over tighten. A loose PCM connector can result in all kinds of weird problems. The next step would be to check for continuity from the PCM connector to the O2 sensor connector. Your PCM O2 pins should be the same as mine: Pin 35 (RD/LG), HO2S #12 Input, goes to the RD/LG wire that connects to the sensor; Pin 91 (GY/RD), Sensor Return, goes to a splice changing to the OG wire that connects to the sensor. If there is continuity then you should check for a short to chassis ground.
