O2 Sensor Reading 0.5v.. Bad ECU??

[bmdubya1198]

Was this a direct replacement O2 sensor or did you have to splice a connection on?

This is an important thing to know here. "Universal" O2 sensors do not play nice with these cars. I think the N/A OEM sensor is Denso, but I might be wrong. Check FCP for part numbers.

[jimmy57]

The front O2 sensor is a wideband and the ECM compares calibration (also called pump current in some descriptions) signal to output signal. If you use a DC voltmeter between the two wires for these signals you should see +0.15 V to -0.15 V as normal range as the fuel trim is oscillated rish/lean in response to exhaust gas oxygen content going up for lean and down for rich. With a scan tool the wide band style used in front position you will see value over 1 for lean and less than 1 for rich. That number is not voltage, it is lambda where exh oxygen content/ideal oxygen content gives >1 lean and exh oxygen content/ideal oxygen content <1 is rich. This can also be explained as fuel-air ratio/ideal fuel air ratio and again the number is more than 1 lean and less than 1 rich.

The heater circuit is controlled and there will be a 12V fixed supply V and the ground will be pulsed. The pulsed ground V will vary to measured current on the heater. Heater current is temp dependent negating need for a temp sensor. 75% ground period would be 3V 50% would be 6V and 25% 9 V . If the heater is not being operated then you will read 12V on both wires to heater element. typically once warmed up you might expect 6-9 V on the heater ground control wire.

I'm unsure what the OBDII dongle thingy is reading. There may be an error in the software for the scan tool. It actually looks right if the #1 and #2 sensors are reversed. Rear sensor should not vary as much and is voltage and normal is .65 to .75 V . The one shown as rear (blue) is wrong as valued for either but looks like a pattern for a properly functioning front if the center point of its oscillation was 1.

[wizechatmgr]

Ah, wide bands sensors =)

I finally got used to the heated vs unheated ones...

[abscate]

The front O2 sensor is a wideband and the ECM compares calibration (also called pump current in some descriptions) signal to output signal. If you use a DC voltmeter between the two wires for these signals you should see +0.15 V to -0.15 V as normal range as the fuel trim is oscillated rish/lean in response to exhaust gas oxygen content going up for lean and down for rich. With a scan tool the wide band style used in front position you will see value over 1 for lean and less than 1 for rich. That number is not voltage, it is lambda where exh oxygen content/ideal oxygen content gives >1 lean and exh oxygen content/ideal oxygen content <1 is rich. This can also be explained as fuel-air ratio/ideal fuel air ratio and again the number is more than 1 lean and less than 1 rich.

The heater circuit is controlled and there will be a 12V fixed supply V and the ground will be pulsed. The pulsed ground V will vary to measured current on the heater. Heater current is temp dependent negating need for a temp sensor. 75% ground period would be 3V 50% would be 6V and 25% 9 V . If the heater is not being operated then you will read 12V on both wires to heater element. typically once warmed up you might expect 6-9 V on the heater ground control wire.

I'm unsure what the OBDII dongle thingy is reading. There may be an error in the software for the scan tool. It actually looks right if the #1 and #2 sensors are reversed. Rear sensor should not vary as much and is voltage and normal is .65 to .75 V . The one shown as rear (blue) is wrong as valued for either but looks like a pattern for a properly functioning front if the center point of its oscillation was 1.

" 5 rivers mechanic"

[bmdubya1198]

The front O2 sensor is a wideband and the ECM compares calibration (also called pump current in some descriptions) signal to output signal. If you use a DC voltmeter between the two wires for these signals you should see +0.15 V to -0.15 V as normal range as the fuel trim is oscillated rish/lean in response to exhaust gas oxygen content going up for lean and down for rich. With a scan tool the wide band style used in front position you will see value over 1 for lean and less than 1 for rich. That number is not voltage, it is lambda where exh oxygen content/ideal oxygen content gives >1 lean and exh oxygen content/ideal oxygen content <1 is rich. This can also be explained as fuel-air ratio/ideal fuel air ratio and again the number is more than 1 lean and less than 1 rich.

The heater circuit is controlled and there will be a 12V fixed supply V and the ground will be pulsed. The pulsed ground V will vary to measured current on the heater. Heater current is temp dependent negating need for a temp sensor. 75% ground period would be 3V 50% would be 6V and 25% 9 V . If the heater is not being operated then you will read 12V on both wires to heater element. typically once warmed up you might expect 6-9 V on the heater ground control wire.

I'm unsure what the OBDII dongle thingy is reading. There may be an error in the software for the scan tool. It actually looks right if the #1 and #2 sensors are reversed. Rear sensor should not vary as much and is voltage and normal is .65 to .75 V . The one shown as rear (blue) is wrong as valued for either but looks like a pattern for a properly functioning front if the center point of its oscillation was 1.

" 5 rivers mechanic"

No thumbs up icon, but pretend there's one here!
I only know the purpose of an O2 sensor... I'm not an expert.

[sfkd90]

I have no reading from my both upstream O2 (neither via scanner nor when I back probe them), but both O2 work fine when I do bench test by heating them with the torch: the voltage raises as I heat the sensor and drops as I remove the torch (as expected). I checked the heating circuit - continuity is good and once plugged to the harness, the voltage of the heating circuit is good as well (it fluctuates around 2V-10V as ECM turn them on and off). With the engine off, the harness delivers constant 13V. .. still puzzled with no signal reading from the 02. Any thoughts?

[abscate]

I don't think you are testing the OXS by just heating them. They need to develop a potential between the Oxygen in the exhaust and the outside - if you have them on the bench the difference is zero.

[wizechatmgr]

The propane test just tells you it's alive and is capable of detecting a differential of oxygen, not necessarily that it's signal is within the range the ECU expects. Laggy O2 sensors may look good during that test.

Do you have any codes set at this point?

[Darkfleet]

Should have updated this. It ended up being my knock sensor. Knock sensor was faulty and activating causing the mixture to change.

[scot850]

Thanks for the update! It is always helpful when we get a resolution update. Hard to figure the knock sensor failing. Not a common error, but sometimes down to bad seating on the sub-frame.

Neil.