Check Engine Light & P0141 After O2 Sensor Replacement

[T.Tech]

The picture is what I think you did when you applied 12v if i understood correctly, with the connector at the ecu and o2 sensor disconnected. If that is the case seems that you have excessive resistance on that wire and with that extra resistance amperage would go down causing the MIL to come on. . sorry for the huge image don't know how to make it smaller.

My next step would be checking for voltage on the white and blue wire like 19963.4lsr5 suggested.

When you say you get 0v is it actually 0 or near zero like .01v because those 2 readings are not the same.

 

[19963.4lsr5]

Check Engine Light & P0141 After O2 Sensor Replacement

T.Tech, are you saying the 96 ECU is capable of measuring heater current and determining if it's bad or not? I can see the 2002 ECU doing this but on the first generation OBDII ECU as well? I wish I had the a FSM for my 97 to see Toyotas definition.

the PDF floating around if for a 2002.


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[19963.4lsr5]

Check Engine Light & P0141 After O2 Sensor Replacement

So I checked the ECM, get 0 volts from the bank 2 connector with the key on. According to the FSM, that is acceptable and the ECM should be operating properly.

To add to my confusion, I checked the bank 1 connector, and got 12 volts, which points to an ECM malfunction, but I'm not getting a P0135 (front O2 issue) code.

Am I looking at the FSM wrong? I would think that 9-14 volts output with the key on would be the correct operation? With the key on, shouldn't voltage be sent by the ECM to the O2 heater? With the key on, I get 12 volts from the front O2 heater connection and 0 volts from the rear O2 heater connection (at the ECM).
Also checked voltage at the connectors with the engine on....get 0.24 volts for the front O2 and still 0 volts for the rear O2.

Rechecked the resistance at the rear O2 again, and that is within spec.

Wanted to check the wiring, so I applied 12 volts from the battery directly to the rear O2 heater circuit with the connector disconnected from the ECM. Measured the voltage at the rear O2 and am getting a constant 4.9 volts. Why would that be? Is there a circuit where the voltage is manipulated? Does the O2 heater operate on 5 volts vs 12 volts?

All of this is leading me to believe the ECM is faulty.....thoughts?

I'd replace it just to check, but manual trans ECMs are way more expensive and rare compared to AT versions, so I'm hesitant.

To me if you on pin 9 of the E7 connector and read 0 volts to ground the transistor is working, or your not getting 12v to the heater at the connector, or your not making good contact with the pin. Pin 3 above it is HT1.

The test saying that your to look for 9-14v on HT1 and HT2 to ground and if ok replace ECM means that if voltage is present on one of those pins with ignition on the transistor in the ECM has failed and is not providing a ground for the sensor heater to turn on.

The H3 H4 connector is the O2 sensors. You should have 12v on pin 2 of each O2 sensor. Pin 1 is the wire the ECU grounds (HT1 or HT2) to turn on the sensors heater.

.

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[onemanarmy]

Thanks for the insight.

I'll dig in again and get some pics of my methods.

I'm using a 96 FSM. My truck is a 96.

The FSM says to check the pins with the key on (engine not running) Engine not on is correct I believe?

I checked the front O2 pin, and get 12 V with key on
I checked the rear O2 pin with the key on, and get 0 volts

I believe this is not correct, and was pushing me to believe the ECM was bad.

I ohm'd the new sensor, and got within spec, per the FSM.

 

[19963.4lsr5]

Thanks for the insight.



I'll dig in again and get some pics of my methods.



I'm using a 96 FSM. My truck is a 96.



The FSM says to check the pins with the key on (engine not running) Engine not on is correct I believe?



I checked the front O2 pin, and get 12 V with key on

I checked the rear O2 pin with the key on, and get 0 volts



I believe this is not correct, and was pushing me to believe the ECM was bad.



I ohm'd the new sensor, and got within spec, per the FSM.

If there is something wrong with the O2 sensor connector and there is a bad connection in either the B+ or the HT2 side you will see zero volts at the HT2 and think it's ok. I don't see a problem with you removing the connector from the ECU and turning on the ignition and seeing if pin 9 now has 12v on it.


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[19963.4lsr5]

Check Engine Light & P0141 After O2 Sensor Replacement

This is even easier. Pull the sensor out of the cat and turn on the ignition and see if the sensor gets hot. That will tell you right away without removing the E7 connector from the ECU.

If it stays cold with you reading 0v between pin 9 and a known good ground you've got issues with either power going to the connector (pin 2 of the sensor connector) or issues with the sensors path to ground (pin 1 on the sensor connector)

If it warms up then I'd look for an air leak allowing fresh air into the exhaust near the sensor causing the sensor to stay dormant or a reading below .5v. Then after the exhaust gets hot it seals up.

You may very well have a bad heater circuit for bank 1 sensor 1 reading 12v at pin 3 with ignition on. But it doesn't code because that sensor is close enough to the cylinder heads that it warms up to 600 degrees on its own just from the EGT. (Exhaust Gas Temp). My 2002 Saturn has no heater element in its bank 1 sensor 1 and my engine goes closed loop within 40 to 60 seconds in the dead of winter.


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[T.Tech]

[MENTION=99144]19963.4lsr5[/MENTION] Yes, the ecu measures amperage as per the repair.manual

This is a circuit code so air leaks will not cause a code to set It doesn’t monitor the temp of the sensor.

I don’t believe you have a bad ecu, I would check if you have voltage at pin 2 the white and blue wire

 

[19963.4lsr5]

[MENTION=99144]19963.4lsr5[/MENTION] Yes, the ecu measures amperage as per the repair.manualView attachment 313195



This is a circuit code so air leaks will not cause a code to set It doesn’t monitor the temp of the sensor.



I don’t believe you have a bad ecu, I would check if you have voltage at pin 2 the white and blue wire

The 2002 manual says it measures current. I question if the 96 does as well.


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[19963.4lsr5]

What engine do you have? I looks like I see part of the 3RZ on the top of the one image. I posted info for the V6. If you have the 3RZ that changes things.

It's the larger E5 connector and HT2 is pin 1 and HT1 is pin 2 same theory.

Below is the ECU location for the 3RZ.

.

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[onemanarmy]

I have the 6 cylinder.

I'm following the simple checks that the FSM outlines.

With the key on, I probed HT1, got 12 Volts
With the key on, I probed HT2, got 0 volts

Which is odd, because I'm getting the rear O2 code, not a front O2 code, but from the readings I'm getting, I should be getting a P0135, but I'm getting a P0141.

So the O2 sensor begin to heat up with just the key on? Or does the engine have to be running?

I tested the ECM at HT1 and HT2 with the engine running (at first cold startup) and got the same results as above.

I also have taken the connector off the ECM and measured the voltage on the ECM pins, and got the same results as above.

I also hooked a 12V wire directly into the harness (disconected from the ECM and measured 5V at the O2 sensor connection end (Pin 2 of the connector)...this is suspect
[MENTION=99144]19963.4lsr5[/MENTION] so you're saying the FSM is correct?

The connection for the O2 sensor is new/clean, no evidence of tampering or damaged wires.

This is the page of the FSM I'm using:

 

[19963.4lsr5]

If you put power on the ht2 wire of the ECU pin 9 then the other end of that wire at the O2 sensor is pin 1.

Pin 2 of the connector is the power source from the EFI relay.

And yes that O2 sensor starts heating at ignition on or the FSM would tell you the engine needs to be running.

You still have the old rear sensor don't you? If so put a battery charger on your battery and plug it into the harness and turn on the ignition and see if it warms up. If no do the same with your new one. Of still no swap them in you cat and see what the new one does. If still no start engine and see if it warms up with the engine running.

You probed the O2 connector after hotting up the HT2 wire and only found 5v at pin 2

This level of troubleshooting is difficult to do remotely.

Like I said earlier. I thing the only way the ECU knows the heater circuit failed is by the amount of time it takes for the ECU to see a valid O2 sensor signal.

your HT1 circuit may very well be bad but the ECU can't detect the fact that the heater never turns on. it's so close to the cylinder heads that the engine exhaust warms up the sensor and the ECM sees a valid switching signal and goes closed loop.






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[onemanarmy]

I installed a new Denso O2, part # from the Denso site.

thanks for your help/insight. I'm gonna troubleshoot some more this weekend and get some pics.

Thanks

 

[19963.4lsr5]

Check Engine Light & P0141 After O2 Sensor Replacement

Since I can't help myself

It won't take but a few minutes of ignition on before it will be obvious if the heater in the sensor is working. This may have been 2-3min and in my shop and you could smell the hot metal.

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[onemanarmy]

Since I can't help myself

It won't take but a few minutes of ignition on before it will be obvious if the heater in the sensor is working. This may have been 2-3min and in my shop and you could smell the hot metal.

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Awesome. I'll see when/if mine gets hot with the key on.

 

[19963.4lsr5]

Check Engine Light & P0141 After O2 Sensor Replacement

If it does not get hot and you have alligator jumpers jam a stripped wire into the back of pin 9 (HT2) and ground it to a good ground and see if it gets hot. If my 97 wouldn't be down for the count I'd put a wire on my HT2 and monitor if the heater is commanded on all the time or not. I'm pretty sure it is being that far away from the exhaust heat.

If the sensor does not get hot you need to look for power on pin 2 of the sensor harness and if it's there then you need to check continuity between pin 1 of the sensor harness and pin 9 of E7 at the ECU.

This is what must be done, and you reading 0v to ground on pin 9 with ignition on I and not expecting it to be hot. The PIN numbers are on the outside of the O2 sensor connector. So it shouldn't be hard to unplug the sensor and look for battery voltage on pin 2 of the harness connector if it doesn't get hot.

This is higher level troubleshooting. You got this. Keep your wits about you and remember what you did, write down your readings so you do not forget or get confused.




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[onemanarmy]

small, interesting update.

unplugged the harness from the rear sensor, turned key on, and got 12V at PIN 2.

So I then took the sensor out of the exhaust pipe and turned key on (connected back to harness) and the sensor didn't get warm after 3-4 minutes. It remained 'room' temp.

What is this telling me? This is a new Denso sensor and I've tested the heater circuit of the sensor and the required Ohm value.

Thanks

 

[TheDurk]

small, interesting update.

unplugged the harness from the rear sensor, turned key on, and got 12V at PIN 2.

So I then took the sensor out of the exhaust pipe and turned key on (connected back to harness) and the sensor didn't get warm after 3-4 minutes. It remained 'room' temp.

What is this telling me? This is a new Denso sensor and I've tested the heater circuit of the sensor and the required Ohm value.

Thanks

Probably that the ECM won't let the O2 sensor heat if the engine is not actually running. Just a guess, but that load would run the battery down pretty fast if the engine were to stall and key were left on.

 

[19963.4lsr5]

Probably that the ECM won't let the O2 sensor heat if the engine is not actually running. Just a guess, but that load would run the battery down pretty fast if the engine were to stall and key were left on.

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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[TheDurk]

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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I stand corrected. I should have read back.

 

[19963.4lsr5]

Check Engine Light & P0141 After O2 Sensor Replacement

I stand corrected. I should have read back.

It's hard keeping track with all the posts. Plus the wording in the FSM is to test if it's bad not good so the tests seem backwards.

Edit. Him showing 0v on HT2 and still getting a sensor heater code could be a bad wire or connection and the 12v from pin 2 of the connector isn't making it to the ECU through the heater element. It not getting hot in 4-5m it sure seems like it. You could smell it in the shop pretty quick hooked up to the power supply.




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