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The FSM describes how to test the O2 sensor using the ecm self-diagnostics. It is the mode 2 running test:zerothread?id=253912

A dirty or old sensor will tend to read lean which would result in a rich condition. o2 sensor does not control the mix at idle!

Testing o2 sensor with volt meter:

This is basically duplicating the mode2 self-diagnostic test. This can be easier than reading the codes off of ecm. If you get a reading other than alternating 1 and o , the information is not that useful as you dont know if the o2 sensor reading is accurate. ie if you get .5 volts which is rich you dont know if that reading is right.

A.O2 sensor disconnected:

Unplug the O2 sensor from harness. Place one probe on sensor wire and one probe on ground. It should alternate between 1 and 0 if mix is optimal.This test makes sense at idle as o2 sensor does not have any say in the mix.

B.o2 sensor connected

The o2 sensor is in the circuit so your test is the same as ecm mode 2 test.Above 1500 rpm, it should altenate between 1 and 0

1 is rich and 0 is lean. a reading from .2 to .85 is optimal. the car has to be heated up by driving. if you sit around idling o2 sensor will get dirty and cool and read lean. if you get a reading above .85 it is safe to say you are rich as the o2 sensor tends to read lean when it is dirty or cool. Location

Under the exhaust manifold of driver side of engine.

ToolsUse an imperial wrench 7/8 inch to get it off. Use anti-seize compound on thread.

http://www.aa1car.com/library/o2sensor.htm

http://www.aa1car.com/library/2004/us10438.htm



Notes:

1. No light means rich and light means lean during oxygen sensor ecu test.

2. The idle will always be rich. This is how the car is designed. California is different because they have different computer. The AIV is there to compensate for the rich idle. However, the aiv is south of the o2 sensor so if you monitor the o2 sensor voltage, the reading will always be rich.

3. The O2 sensor will cool down almost immediately after you stop and start idling. So, the o2 sensor will read lean during idle ie .5 vs .8.

4. The o2 sensor wire is shielded wire which means there is a metal layer to prevent electromagnetic interference. This metal shield is grounded by the ecu. dont ground directly to engine ground. dont let the shield touch the core. Google splicing o2 sensor wire for info on repairing.

http://auto.howstuffworks.com/....html

http://books.google.com/books?...um=10
Modified by vancouverbc at 2:54 AM 6/28/2009