Dr-4 - Code 21 - O2 Sensor Circuit
- Turn ignition off, connect DRB-II and disconnect O2 sensor connector. Turn ignition on. Put system in Sensor Test Mode "02". Refer to ENTERING ON-BOARD DIAGNOSTICS in this article. If display on tester is at least .4 volt, go to next step. If display on tester reads zero volts, replace SMEC. Before replacing SMEC, ensure Black/Dark Green wire at cavity No. 23 of SMEC 60-pin connector is not shorted to ground.
- With system in Sensor Test Mode "02" and O2 sensor disconnected, connect one end of a jumper wire to Black/Dark Green wire of oxygen sensor harness connector. Connect other end to battery positive post. If display on tester reads at least 5 volts, replace O2 sensor. If display on tester reads .4 volt, repair Black/Dark Green wire of O2 sensor connector for an open circuit to SMEC.