Oxygen (O2) Sensor Current Feed & Heater Resistance

Check O2 sensor current feed. Remove panel under right side of instrument panel. Disconnect fuel system relay connector. See Figure .
Energize fuel pump. To do so, connect a jumper wire between terminal No. 30 and No. 87/2. On 240 and 240 DL, connect a voltmeter between ground and O2 sensor Yellow/Red wire.
On 740 GL, 740 GLE, 760 GLE, and 760 Turbo, connect voltmeter between ground and O2 sensor Pink wire.
On 740 Turbo, connect voltmeter between ground and O2 sensor Green wire. On all models, voltmeter should read 12 volts. Remove jumper wire from fuel system relay.
Ensure ignition switch is in OFF position. Check O2 sensor preheating resistance. Ensure engine temperature is below 68°F (20°C).
On 240 and 240 DL, connect an ohmmeter between ground and O2 sensor Yellow/Red wire.
On 740 GL, 760 GLE, 740 GLE, and 760 Turbo, connect an ohmmeter between ground and O2 sensor Pink wire.
On 740 Turbo, connect an ohmmeter between ground and O2 sensor Green wire.
On all models, resistance should be as specified. See the OXYGEN SENSOR HEATER RESISTANCE table. Disconnect ohmmeter. Start and run engine to operating temperature. Turn off engine.
Reconnect ohmmeter to O2 sensor Yellow/Red wire (240 and 240 DL), Pink wire (740 GL, 740 GLE, 760 GLE, and 760 Turbo) or Green wire (740 Turbo). Check that resistance increases when engine goes from cold to normal operating temperature.

OXYGEN SENSOR HEATER RESISTANCE

Temperature °F (°C)	Ohms
68 (20)	3
660 (350)	13