Check Engine Light & P0141 After O2 Sensor Replacement

19963.4lsr5 said:
According to his FSM test its key on and no start. To me either the wire is bad between the sensor and the ECU or the transistor is bad. I remember he said he had 12v on the ECU pin at key on, which seems like an open transistor. If he doesn't have 12v at the ECU with the O2 sensor plugged in then it seems like a connector pin or wire problem.

he may be able to ground the wire and it may be ok. That will allow the heater to work and I think the ECU won't code because it sees a valid O2 sensor signal in time.


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Click to expand...

I'm not sure a full time ground is a good idea. The ECM only heats the sensor when it thinks it needs it;

From the '96 EWD:

HEATED OXYGEN SENSOR HEATER CONTROL SYSTEM
THE HEATED OXYGEN SENSOR HEATER CONTROL SYSTEM TURNS THE HEATER TO ON WHEN THE INTAKE AIR VOLUME IS LOW
(TEMP. OF EXHAUST EMISSIONS LOW), AND WARMS UP THE HEATED OXYGEN SENSOR TO IMPROVE DETECTION
PERFORMANCE OF THE SENSOR. THE ENGINE CONTROL MODULE EVALUATES THE SIGNALS FROM EACH SENSOR (INPUT
SIGNALS (1, 3, 7, 8, 10)). CURRENT IS OUTPUT TO TERMINAL HT1 OR HT2 AND CONTROLS THE HEATER.
Click to expand...
 
That makes sense to me Durk.

Why didn't I see that in my 97 you sent me or the book I bought darn it!




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Onemanarmy use a test light to test for 12v at the O2 sensor connector. A high resistance connection will show 12v on a DVM because of the high impedance.

Using a test light will make the connection work and if it's bad you will get no bulb or a dim bulb.


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19963.4lsr5 said:
According to his FSM test its key on and no start. To me either the wire is bad between the sensor and the ECU or the transistor is bad. I remember he said he had 12v on the ECU pin at key on, which seems like an open transistor. If he doesn't have 12v at the ECU with the O2 sensor plugged in then it seems like a connector pin or wire problem.

he may be able to ground the wire and it may be ok. That will allow the heater to work and I think the ECU won't code because it sees a valid O2 sensor signal in time.


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Click to expand...

So PIN 2 get the 12V from the ignition wiring/EFI wiring (not through the ECM)? The ECM 'grounds' PIN 1?

Ground what wire? The PIN 1 wire? I guess I could cut the sensor wire and manually ground it/ground through an external switch, and then it should get hot. It gets 12V with key on, I've Ohm'd the resistance of the sensor (got within spec)...stands to reason that the sensor should heat up.

As per my previous troubleshooting, I tried to send 12V down the line to PIN 1 to make sure the wire wasn't cut, and got a reading of constant 5V. Odd, yes. I will repeat this.

With the key on, should i get a voltage reading at PIN 1? is there anyway to isolate the ECM function? I recall getting 0.1-0.2 V, but I'll have to check again. When you say transistor could be bad, you mean ECM internal issues?

Thanks for everyone's help.
 
onemanarmy said:
So PIN 2 get the 12V from the ignition wiring/EFI wiring (not through the ECM)? The ECM 'grounds' PIN 1?



Ground what wire? The PIN 1 wire? I guess I could cut the sensor wire and manually ground it/ground through an external switch, and then it should get hot. It gets 12V with key on, I've Ohm'd the resistance of the sensor (got within spec)...stands to reason that the sensor should heat up.



As per my previous troubleshooting, I tried to send 12V down the line to PIN 1 to make sure the wire wasn't cut, and got a reading of constant 5V. Odd, yes. I will repeat this.



With the key on, should i get a voltage reading at PIN 1? is there anyway to isolate the ECM function? I recall getting 0.1-0.2 V, but I'll have to check again. When you say transistor could be bad, you mean ECM internal issues?



Thanks for everyone's help.
Click to expand...



Do the 12v check on pin 2 of the sensor with a test light first.

You may be able to jam a stripped wire into the back side of the HT2 and ground it.

It would be good for you to check the resistance of the wire between HT2 pin on ECU and pin 1 of the sensor if the test light is lit and bright on pin 2.


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onemanarmy said:
So PIN 2 get the 12V from the ignition wiring/EFI wiring (not through the ECM)? The ECM 'grounds' PIN 1?

Ground what wire? The PIN 1 wire? I guess I could cut the sensor wire and manually ground it/ground through an external switch, and then it should get hot. It gets 12V with key on, I've Ohm'd the resistance of the sensor (got within spec)...stands to reason that the sensor should heat up.

As per my previous troubleshooting, I tried to send 12V down the line to PIN 1 to make sure the wire wasn't cut, and got a reading of constant 5V. Odd, yes. I will repeat this.

With the key on, should i get a voltage reading at PIN 1? is there anyway to isolate the ECM function? I recall getting 0.1-0.2 V, but I'll have to check again. When you say transistor could be bad, you mean ECM internal issues?

Thanks for everyone's help.
Click to expand...

Well, if you had 12V+ on Pin 1 and the ECM was not providing ground, a reading of 5V is reasonable, because the heater would be acting as a resistor. In that case, it would point to a bad ECM or the wiring to it. (Maybe it is not getting the correct input, so it thinks not providing ground is the correct thing to do.) If the ECM is providing ground as it should, then the voltage would be zero (ground continuity.) O.1-0.2V is also fine, accounting for the resistance of the ECM circuitry.

I'm not looking at the FSM, I'm just saying what makes sense to me looking at the EWD,
 
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Yea...all that makes sense.

Took the O2 sensor out and put dedicated 12V to it, it got too hot to touch in 2 mins. So the sensor is working.

I'll get a test light on it and see if the light is bright and re-do my resistance tests.

Thanks again
 
Update:
-The O2 sensor heats up in about 2 mins when I connect it directly to the battery.

-I have 12V at pin 2 (at O2 sensor connection) with the key on.

-I unplugged the connector from the ECM, ran 12V down HT2 and checked voltage at Pin 1...saw 4.89 volts (close to the 5V I saw earlier)....weird?

-With key on and connector still unplugged I saw 4.2 volts at HT1 and HT2 coming right out of the ECM. FSM says 'no good' if I see 9-14 volts....but the FSM appears to not be worded correctly. Not quite sure here.
Also, if I was reading 4.89 volts, this is close to the 4.2 volts I saw coming out of the ECM, so why won't it ground itself and heat up?

-For the time being, it appears that I have a grounding wire/circuit issue in between the ECM and the O2 sensor connector, which is quite bad, who knows where that wiring is in the wiring harness. I've thought about creating a dedicated switched ground for the rear O2 sensor, but that is janky as well. Again, this is quite strange, as I have done no wiring mods and the vehicle has not had any wiring work done to it and the problem just popped up one day.

Anything else to check?

Thanks again
 
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With the O2 sensor unplugged you should have seen 12v at the sensor connector in my opinion. Not 5v. Send the 12v down the wire again and see if it will light a test light

But sadly to me it still looks like the ECM transistor or its control circuit has failed.


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19963.4lsr5 said:
With the O2 sensor unplugged you should have seen 12v at the sensor connector in my opinion. Not 5v. Send the 12v down the wire again and see if it will light a test light

But sadly to me it still looks like the ECM transistor or its control circuit has failed.


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Yes, I agree. There should not be a reason why the voltage would drop from 12 to 5, as far as I know. Should be an un-interrupted wire from the connector to pin 1....?

The ECM is showing 4.2V steady at HT1 and HT2 pins with key on
 
You could try redoing the engine and frame grounds. But I doubt that's the problem. Wish you were closer too me.


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To me if you have the connector off the ECU and the O2 sensor and have battery voltage on the wire going down to the O2 sensor there is a wire problem or a connection problem between each end of the wire. Resistance check with an ohm meter would be better.

Find a small pin etc and extract both the HT 1 and 2 wires and give them a ground. If the code goes away rig up a relay to an ignition circuit and be done with it or get a reman ECM


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Yea...I'm thinking about manually switching/grounding PIN 1 somehow. When I took the O2 sensor out and tested it, I used the 12V from the connector and manually grounded it with some wire and it heated up properly.

Now, after seeing 4.2 V at HT1 and HT2 right out of the ECM with the key on, I'm not quite sure what to think...Would that be enough of a 'ground' to ground the O2 sensor? Again, the FSM states that 9-12V is out of range.
The 4.2 V is making me think the ECM is ok.

What should the resistance on the wire be if all is well? I guess zero ohms would tell me there is a break somewhere.

Thanks
 
onemanarmy said:
Yea...I'm thinking about manually switching/grounding PIN 1 somehow. When I took the O2 sensor out and tested it, I used the 12V from the connector and manually grounded it with some wire and it heated up properly.

Now, after seeing 4.2 V at HT1 and HT2 right out of the ECM with the key on, I'm not quite sure what to think...Would that be enough of a 'ground' to ground the O2 sensor? Again, the FSM states that 9-12V is out of range.
The 4.2 V is making me think the ECM is ok.

What should the resistance on the wire be if all is well? I guess zero ohms would tell me there is a break somewhere.

Thanks
Click to expand...



Your meter should read less than 1ohm measuring the length of wire between the ECM connector and the O2 sensor connector. I'd measure mine but it's down for an engine rebuild.


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So...thinking more about using a relay to bypass the computer and wiring, and am trying to understand the logic.

The sensor gets 12V switched power (not ECM controlled)...I believe this is correct?
The ECM is responsible for the 'grounding' to control current flow....correct?
So if I wanted to bypass the ECM...I would need a relay to ground the sensor when the key is on.

However, I don't know how long the sensor stays on.....is it timed? That seems the most reasonable way it would be controlled, as there isn't a temp sensor on the O2 sensor. How would I trigger it to cut off at a certain time? Would it hurt it to stay 'heated' at all times when the key is on?
 
Check Engine Light & P0141 After O2 Sensor Replacement

For now a simple toggle switch will work. The O2 sensor before the cat only needs heated during warmup.

The sensor after the cat is much farther away. If the ECM does cycle that heater on and off its probably based on the predicted cat converter temperature. I don't think you will burn out the heater leaving it on.

However you could turn off the rear sensor heater after say 20min and see if you get a code.

Thinking about this some more. If there is a pull up resistor in the control circuit for each transistor, that would be a way they could detect a open or shorted heater circuit. And your relays will operate the heaters but the ECM will be sensing a high voltage on the HT1&2 sensing circuitry And still code. You won't know this until you try.

Did you measure the resistance between the HT pin and the Sensor pin to check for high resistance yet?


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