O2sensorplugs

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Oxygen (O2) sensor testing

16 valve O2 sensor wiring.

This photo shows the oxygen sensor (also called "Lambda" sensor) wiring for a 1990 Saab 900 with 16V engine. The two white wires are for the O2 sensor preheater, while the single black wire is for the signal which the sensor sends to the LH-injection system computer.

A DVOM (digital volt/ohm meter) is required to do this test, since such meters have high input impedance.
Use a meter with at least 10 Megaohm impedance to avoid damage to sensitive circuitry inside the LH-Jetronic system computer.

1. Testing of preheater function is done by unplugging the white wires' connector plug. Then, set DVOM to a range which covers 12 volts DC, connect the leads of meter across the two terminals inside the plug (on fender side, not O2 harness).
With engine running, there should be battery voltage (~ 12-14V).
If not, then the fuse (inline with wires '86 to '88 models, in main fusebox on 1989-on cars) or wiring are suspect.

2. Testing of O2 sensor signal sending funciton is done by leaving black wire connected (see above) and wiggling back the black rubber boot from the orange connector plug to expose the metal terminal connection. (Again, use a DVOM for this test, and set it to a scale which will measure 1 volt or less.) With engine running and at operating temperature, connect the positive (red) lead of the meter to the O2 sensor black wire terminal, being careful not to let either the terminal or meter positive lead touch ground.
Then, touch the negative (black) lead of the meter to the car body, a screw head, engine block, valve cover, etc. (any ground point).
Voltage should fluctuate between 0.2 and 0.9 volts--centering around 0.5 volts--as the LH-Jetronic system continuously varies engine mixture. If the meter shows no voltage, first make sure you have a good ground before condemning the O2 sensor. If the voltage stays on one value, the sensor is probably faulty.

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Note: 8V O2 sensor plug photo is below.

This photo shows the 8V O2 sensor on the pass. side inner wheelwell, shown unclipped from its holder. Black wire leads to O2 sensor on a non-turbo exhaust manifold in background. Peel back and push black rubber boot down the wire a bit to check voltage with positive lead of digital volt/ohm meter. Ground negative lead to a screw on body or safe point on engine. For voltages, see 16V test procedure above.