Dr3 - Code 21 - Oxygen Sensor CKT To Logic Module

With diagnostic readout tool connected to engine harness connector, turn ignition switch to "OFF" position. Unplug oxygen sensor connector. Enter system into Sensor Test Mode 02. Divide reading on display by 10. If display reads at least .4 volt, go to next step. If display reads zero, logic board is defective. Replace engine control module.
NOTE: Before replacing engine control module, ensure that wire of cavity No. 23 of 60-way connector is not damaged causing poor connection.

Fig 1: Distributor Pick-Up Harness Connector

Fig 2: Heated Oxygen Sensor Harness Connector & Battery
With O2 sensor disconnected, connect one end of jumper wire to Black wire of O2 sensor harness connector. Connect other end of jumper wire to battery positive terminal. If display does not read at least 5 volts, replace O2 sensor. If display reads .4 volt, check Black wire of O2 sensor connector for an open circuit to engine control module.

CAUTION: DO NOT connect jumper wire between battery positive terminal and center terminal (ground) of O2 sensor connector.