Technical fiat grande punto 1.4 tjet o2 sensor problem

[Bernievarian]

A typical O2 sensor would have a resistance between 10 and 20 Ω, draw between 0.6 to 1.2 A or dissipate between 7.2 to 14.4 watts.

I would directly feed the heating element with 12VDC THROUGH a 5W bulb, if it doesn't lit your heater is open ... Can't test it simpler !!

BRs, Bernie

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[Bernievarian]

O2 sensors will read 0.45v for about 2-3 minutes after a cold start...only after the car heats up enough it will go into closed loop mode then the O2 values will oscillate.

I'm afraid I have to (partly) disagree ...

O2 sensors don't output anything (they're basically generators) when they are cold. Only once they're warm enough their ouput will oscillate between (typically) 0.15 and 0.75V, witch averages @ 0.45V, which correspond to 14.7 A/F ratio.
During heat-up time, the ECU ignores the O2 signals and uses a fixed enrichment value.

Did you red the 0.45v in-situ or was it MES reading ?

BRs, Bernie

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[aurick86]

During heat-up time, the ECU ignores the O2 signals and uses a fixed enrichment value.

Did you red the 0.45v in-situ or was it MES reading ?

Yes, Bernie, that is what i should have said.... it's what i meant to say.

 

[aurick86]

Yes, Bernie, that is what i should have said.... it's what i meant to say.

AND
The ECU will show a fixed value ~0.45v on the O2 sensors... I don't think it's actual voltage at the sensor... it's just the value the ECU uses during the heating up phase.

 

[Bernievarian]

100% agree with the last 2 posts ...

BRs, Bernie

 

[webmusta]

i can heat the o2 sensor with direct 12volt.
so i know the heater worinkg in the o2 sensor.

 

[webmusta]

but can you explain why i get voltage drop to 0volt when i connect the o2 sensor

 

[Bernievarian]

i can heat the o2 sensor with direct 12volt.
so i know the heater worinkg in the o2 sensor.

As we know now that the heater is ok, let's proceed to the next test:

- connect pin 4 to battery +12V (thru the bulb)
- leave pin 3 connected to the ECU (return path)
- if the heater heats: the return path (ECU) is ok
- if not: the return path (ECU or wiring) is bad
- replace the wiring and re-test will tell who's bad

If the heater heats:

- connect pin 3 to battery -12V (thru the bulb)
- leave pin 4 connected to the distribution box (feed path)
- if the heater heats: all is fine (which we know is not)
- if not: the feed path (fuse or wiring) is bad
- replace the wiring and re-test will tell who's bad

The 12V you see when the O2 sensor is not connected is probably a floating voltage you see thru a pull-up or pull-down resistor inside the ECU. So I think the ECU is the source of your problem...

We'll see with that test.

BRs, Bernie

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[aurick86]

but can you explain why i get voltage drop to 0volt when i connect the o2 sensor

How/where are you measuring?

If it's PWM i wouldn't trust the readings of a multimeter, you need an oscilloscope.
Does the bulb still light up in parallel with the O2? or 12v on one side and grounded on the ecu controlled ground for the O2.

 

[webmusta]

thanks to all for your help. i dont know how but its work now. its heat up and it mesure the correct value for o2 sensor now

 

[aurick86]

thanks to all for your help. i dont know how but its work now. its heat up and it mesure the correct value for o2 sensor now

99% it's one of the following: a connector or wire shorting or ecu controlled ground touching ground messing how ECU checks O2 sensor.