Code P0139 - Secondary Heated Oxygen Sensor (Ho2S)
- Connect and operate scan tester, following manufacturer's instructions. Clear codes. Start and run engine at 3000 RPM until fan comes on, then run at idle. Quickly increase engine speed to 5000 RPM, then release throttle. Read secondary HO2S output. If output does not remain within 0.45-0.55 volt for one minute, go to next step. If output remains within 0.45-0.55 volt for one minute, temporarily substitute known good secondary HO2S, then retest system.
- Turn ignition off. Unplug secondary HO2S connector. Start and run engine at 3000 RPM until fan comes on, then run at idle. Measure voltage between Blue and White wires at secondary HO2S terminals. If voltage is greater than 0.1 volt, go to next step. If voltage is not greater than 0.1 volt, temporarily substitute known good secondary HO2S, then retest system.
- Turn ignition off. Reconnect wiring to secondary HO2S. Start engine. Measure voltage between ECM terminals D14 (Blue/Red wire) and D22 (Green/Blue wire). If voltage is greater than 0.1 volt, repair open or shorted Blue/Red or Green/Blue wire between ECM and sensor. If voltage is as specified, temporarily substitute known good ECM, then retest system.