O2 sensor plug volts??
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From: South of Augusta,GA
O2 sensor plug volts?? Im trying to figure out why my passenger side O2 sensor reads only 430-455 all the time. Driver side reads right 400-900(Arero Force gauge) I switch sensors from one side to the other, and they both work on driver side. I was checking volts at the plug for the sensor, and only see 0.20volts pass side/0.21 driver side. I was thinking I should see 12 volts at each plug? The harness came from a 2000 Sliverado, LQ4 engine. The wires going to pass side plug are A=Tan/B=purple/D=LT Green-wht/E=LT Green. They dont have 12volts on either side, but driver side works. Sensors are new, thanks for any help, did a search, and cant find info on plug prong out puts. This is a swap into a 1981 T/A, harness has been mod by me, what should I check?
The 12v is only for the heater and should be there any time the key is on. C & D are the heater power and ground. A & B are the signal and ground. The voltage staying at 450 mv is a default when the sensor/circuit is open. Check the wires from the pcm to the O2 plug and make sure that it is correct. Also make sure your heater wire is getting power with the key on.
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From: South of Augusta,GA
Ok trying to understand. It showed 12.35 volts until the engine got warm at the LT-Green/Wht wire. After that its go to 0.20 same wire. Arent the sensors grounded thru the maniflolds? I dont have a pink, and Blk wire.
Can you be more specific on what vehicle the wiring harness came out of. On some vehicles the PCM provides the +12 for the heater and the wiring schematic will be different.
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From: South of Augusta,GA
Dont have exact truck it came out of, got the engine,PCM,and most of the harness from a salvage yard. I just was told it was a pick up, with a 6.0, I know it had a 4l80 trans. The plugs for the O2 sensors plugs are triangle shaped, and different from most trucks. So do the sensors need 12volts all the time? If I unplug the sensor while car is running it stumbles! Maybe my gauge is just not reading it? The spark plugs on that side of the engine are really clean. The car runs good to me, but I didnt want to hurt anything by not seeing it show reading. The volts while running from the purple wire jumps around .20-.86 aprox.
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Launching!
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From: Manitowoc wi.
The Lt.green/white wire is the b+ supply wire from the pcm for the o2 sensor heater only. This cicuit is then grounded at the pcm via the green wire which then monitors sensor heater operation until proper temperature is achieved. Once this occurs the ground is then removed and the second circuit consisting of the purple and tan wires is used. The voltage on the purple wire is usually a steady .45 volts to the sensor. As the sensor changes temperature with leaner or richer mixtures it crosses this voltage and is returned to the pcm on this same line. However the tan wire must be grounded in order for this to happen. Most all of these grounds are done thru common ground terminals on the engine block and then back to the ecm. On this particular application the gound is done by the pcm on terminals 26 and 29 of the blue connector cicuit #413. All 4 o2 sensors use this circuit but come back to different pins on the pcm. There were 2 designs used by GM in this year, all with case grounded 02s and those with isolated grounds. Check the continuity of the tan wire back to the ecm pin 26 Bank 1 Sensor 1 and pin 29 Bank 2 Sensor 1 for opens. If these are OK replace the faulty sensor
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From: South of Augusta,GA
Ok, thanks alot. I grounded the tan wire on the engine, and it still reads 445-450, green/wht wire dont show 12volts, maybe 2, but it did show once when car was cold. Purple wire shows volts going from 01-090 jumps around as engine run. is it possible that the gauge is not reading it, but the PCM can see it? Car seems to run great, it was just wondering why the driver side go from 400-800, but pass side stays at 435-450. If I unplug pass side sensor while car is running it stumbles, so do that mean the PCM sees it? I have a volt meter, but not sure how all the setting work, how do you check continuety, what would I set it to , and what am I looking for. I know how to check for volts.
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From: South of Augusta,GA
ok took battery charger hook to wires at sensor plug, and I get 12 thru tan wire at the computer harness 26/29, also hook purple wire up got 12 to the harness plug were it plug into the PCM. Do I need to check the LT/Green-WHT, and lt Green? IF they checkout then what? Do I need to ground the manifolds?
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From: South of Augusta,GA
That has the right colors, thanks. I checked all the wires from the sensor to the PCM, no breaks. Think I need to ground the manifold? Ran 12 volts thru 26/29/66 pins all of them work.
L-trims= Long Term Fuel Trims by the PCM based on the output millivolts from the O2 sensor. Usually when it's flatlined like that the PCM is discarding the reading for some reason. If the L-trims are normal....-8 to+8 I would get someone to scan it with a GM Tech2.
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From: South of Augusta,GA
L-trim showing -1.5 idle, is that good?
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yes go to 900-950 on the driver side sensor, pass side stay around 450. is it possible the PCM sees it but dont display it? As i said it runs great, all the wires work, and a signal is being sent on purple wire.
Launching!
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From: Manitowoc wi.
Clip your test meter leads to the purple and tan wires on the o2 sensor connector with the sensor unplugged.Make sure that your meter is connected to the o2 sensor side. Connect a jumper wire from the tan lead to ground and see what the readings are. Since the o2 creates its own voltage it should fluctuate from lean readings.10 to .45 to rich .50 to .90. You can temporally richen the mixture by blipping the thottle while watching the response on your meter.
It's the scan tool not seeing it correctly. I have seen this many times. Just don't know why. Bet if you look at it with another scan tool it will look fine.