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Old 07-09-2016, 11:52 PM   #1
Halsey2016
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Question Need o2 sensor help


I have 4 o2 sensors. 2 of them are ready no activity. What can cause this problem?

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Old 07-10-2016, 05:06 AM   #2
derfderf
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Please state year and model (L300, LW300,.....)

Sounds like you are trying to interpret some DTCs (diagnostic trouble codes).

Please list each code as Pxxxx where x is a number.
We'll take it from there.
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Old 07-10-2016, 09:21 AM   #3
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2000 LS2 V6 3.0
P0030
P0050

When these 2 sensors are put to a voltmeter they read nothing but when the other 2 are put to it they read 12 volts
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Old 07-10-2016, 03:45 PM   #4
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P0030 HO2S Heater Control Circuit (Bank 1 Sensor 1)

P0050 HO2S Heater Control Circuit (Bank 2 Sensor 1)

These codes are for the upstream heated O2 sensors coming off the exhaust manifold (pre cat con).

Bank 1 is for the bank of cyls containing cyl #1, bank 2 is the bank of cylinders not containing the #1 cylinder. Sensor 1 is pre cat, Sensor 2 is post cat..
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So it sounds like from the codes and your measurements that these 2 pre cat sensor heaters are not getting current to their heater circuits. I'm going to make the assumption that the two heater circuits get their 12V feed from the same battery feed through the same fuse. The rear 02 sensors must get their sensor heater current from another similarly configured wiring setup.

The fact that the rear sensor HEATER circuits are reading 12V constantly means the ECM is providing the ground to keep the circuit live all the time. Thus I would expect the same behavior from the front HEATER circuits.

There are 4 basic possibilities:

1) blown fuse on circuit that contains heaters
2) heaters on both circuits have failed simultaneously (assuming both codes were thrown at exactly the same time=failed 02 heater circuits and therefore sensors(both))
3) break in 12V wiring BEFORE the wiring splits to feed each front O2 sensor HEATER
4) bad HEATER ground issue AFTER the sensors. No idea if they come back and meet as a common ground after the sensor but it would make sense that they if they share the 12V feed, they MAY share a ground. Could be a separate ground or could go into a ground splice pack

Likelihood

1, 3/4, 2

1 and 3 can be simultaneously indirectly checked by measuring the 12V side of the sensor relative to FRAME ground. If you get 12V, you know that the fuse is intact AND that the wiring leading up to the sensor is good. That leaves grounding issues or both failing at the same time which is highly unlikely unless the control circuit for them has been toasted and the heaters received some type of current spike that wrecked them.

4 can be initially checked by measuring the ground side of the heater wire to FRAME ground. They should be close to 0 Ohms (continuous). If they are not, then there is prob a wiring break betw the ground side of the sensors and wherever they are wired to ground

2 is the fallback if you cannot find any other breaks in the circuits. Be 100% POSITIVE you can find no other explanation before replacing these as they are $$ and I don't want you to spend $$ only to find out they were not the issue. Again, if the 2 codes popped simultaneously, it is much more likely to be a fuse, wiring, or grounding or ECM issue.
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I lean towards fuse or broken wiring before they split the 12V feed or after they come together before ground.

Since you measured no voltage drop across the heater itself, there is seemingly no current flowing the sensor --hence fuse or wiring break --> no current in circuit.
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A wiring diagram will obviously save you time on both the fuse checks and wire colors pre split. Sorry but I do not have one. An internet search for one or for supporting info is certainly worth your time.
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PLEASE come back to this thread to add to the database of information we have. Many people do not and it is rather frustrating from this end to spend a significant amount of time diagnosing, only to NEVER find out what the problem actually was/if my troubleshooting logic was flawed.

Thanks.

Derf
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Last edited by derfderf; 07-10-2016 at 03:49 PM..
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Old 07-10-2016, 05:33 PM   #5
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Thank you, I will let you know what I find out!
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Old 07-10-2016, 05:53 PM   #6
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I also have a coolant level light on but my coolant level is full, could it be the ects sensor. keeping the ecm from sending 12 volts to the o2 sensor
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Old 07-11-2016, 08:59 AM   #7
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ECTS lets engine infer engine temp from coolant temperature. This parameter is constantly monitored by the ECM to adjust ail/fuel ratios among other things.

Took me a couple minutes to realize what you were really asking, which I think is " if the PCM thinks the car is warmed up, does it kill the heaters to the front O2's?

My GUESS is no, based primarily on the fact that the post cat rear O2s are supplied 12V continuously, and it is hot as hell back there, and therefore the same logic should apply.

But it does not.

I suppose it is remotely possible that the ECTS has failed and ECM thinks the engine never warms up so it leaves the heaters on all the time and the HEATERS burn out, instead of just leaving them on for time needed to heat the sensor at startup.

I simply do not know the setup of an L car well enough of the top of my head to tell you one way or the other.

Easiest way to tell is to hook up a scanner w real time data readout and monitor the ECTS temp as the car warms up. If it changes appropriately, that's not your issue.

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The low coolant light is not connected to the ECTS as far as I know. One provides temperature information, the other is a level sensor.

The coolant reservoir usually has a sensor at the very bottom of it. Over time it gets "gunked up" and no longer performs properly. Also, the wiring at the connector can become a problem, so check the wiring first.

People w S cars have this happen as well. They remove the reservoir from the car and soak it with a warm soapy Dawn solution, then rinse, repeat, rinse, and rinse the hell out of it to get the residual soap out of the reservoir. Then reinstall, reattach the connector, refill, and all should be well
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Old 07-16-2016, 05:49 PM   #8
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Any progress to report?
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