O2 Sensor problem

[davejo...@gmail.com]

The check engine light came on in my 97 Geo Prizm (almost identical to
a 97 Toyota Corolla). The code was P0141 (O2 Heater Circuit (Bank 1,
Sensor 2)) and the Chilton manual said that
that was the post-convertor O2 sensor. It had a little diagnostic test
I could try and so I tried that out and according to the test it was
bad. I replaced the sensor on Saturday, but then today on the way to
work the check engine light came on. It was the exact same code. Does
anyone have any suggestions on what the problem might be?
Thanks,
Dave

[Ray O]

<davejo...@gmail.com> wrote in message
news:1156902858.1...@p79g2000cwp.googlegroups.com...

If you used an aftermarket O2 sensor, the problem may be with the sensor,
especially if you had to snip and join wires.

I would do the same check on the replacement sensor to see if it checks good
or bad. Keep in mind that you are checking the heater circuit and not the
O2 sensor operation. If the O2 sensor heater check out OK, check the heater
circuit wires back to the ECU for an open or short.
--

Ray O
(correct punctuation to reply)

[davejo...@gmail.com]

Ya, the sensor I used was a "universal O2 sensor" that I had to snip
and join to the existing plug. I'll do the same check and I'll look for
a problem in the wiring.
Thanks,
Dave

[Ray O]

<davejo...@gmail.com> wrote in message
news:1156945943....@74g2000cwt.googlegroups.com...

[Ray O]

<davejo...@gmail.com> wrote in message
news:1156945943....@74g2000cwt.googlegroups.com...

> Ya, the sensor I used was a "universal O2 sensor" that I had to snip
> and join to the existing plug. I'll do the same check and I'll look for
> a problem in the wiring.
> Thanks,
> Dave

The need to snip and splice is one of the big reasons I am not a fan of
aftermarket O2 sensors. They live in a pretty harsh environment, exposed to
exhaust heat as well as road debris, water, snow, etc. The factory
connectors are designed for this environment, while many DIY splices become
the weak link. IMO, the extra cost of a factory O2 sensor is worth the
reliability and with a known longevity.

Let us know how you make out!

[davejo...@gmail.com]

This is probably a dumb question, but how do I check if there's a
problem with the connection between the ECU and the O2 sensor?
Thanks,
Dave

[Ray O]

<davejo...@gmail.com> wrote in message
news:1157054292.9...@i3g2000cwc.googlegroups.com...

> This is probably a dumb question, but how do I check if there's a
> problem with the connection between the ECU and the O2 sensor?
> Thanks,
> Dave

It is not a dumb question. The way to check for a problem in the circuit
between the ECU and O2 sensor is to check for continuity, basically zero
resistance, between the O2 sensor and the corresponding pin on the ECU
connector. It helps to have about a 5 or 6 foot long piece of wire to
extend the reach of your ohm meter.

While you are checking, make sure the wire that leads into the pin on the
ECU connector is not loose, and make sure the splice connection you made at
the O2 sensor is good. In fact, I'd start by checking continuity in the
wire before and after your splice.

Also, with the ignition off, you want to check for continuity between the O2
sensor circuit wires and ground. I doubt if this is a problem unless the
vehicle was in an accident or heavily modified where wire harnesses were
disturbed.

[Jeff Strickland]

I'd look at the connections, not the wiring.

<davejo...@gmail.com> wrote in message
news:1156945943....@74g2000cwt.googlegroups.com...

[Jeff Strickland]

"Ray O" <rokigawaATtristarassociatesDOTcom> wrote in message
news:e19b2$44f5b1ca$44a4a10d$60...@msgid.meganewsservers.com...

>
> <davejo...@gmail.com> wrote in message
> news:1156945943....@74g2000cwt.googlegroups.com...
>> Ya, the sensor I used was a "universal O2 sensor" that I had to snip
>> and join to the existing plug. I'll do the same check and I'll look for
>> a problem in the wiring.
>> Thanks,
>> Dave
>
> The need to snip and splice is one of the big reasons I am not a fan of
> aftermarket O2 sensors. They live in a pretty harsh environment, exposed
> to exhaust heat as well as road debris, water, snow, etc. The factory
> connectors are designed for this environment, while many DIY splices
> become the weak link. IMO, the extra cost of a factory O2 sensor is worth
> the reliability and with a known longevity.
>

I second.

[Jeff Strickland]

Also, the circuit operates on milivolts or some very low logic voltage like
that. I don't really know or care, my point is, any problem with the
connection points will translate into poor operation of the system.

This is one of those circuits that must perform to a certain level within a
specific time frame, then do something different within another time frame,
then report what it detects every so often -- a period of several times per
second. The long and the short is that the signal is actually very
complicated, and a poor connection will make the signal shape -- time and
level -- be incorrect for what the computer is looking for. The result is
that the signal is out of range, and the Check light will come on.

"Ray O" <rokigawaATtristarassociatesDOTcom> wrote in message

news:aa91e$44f76857$44a4a10d$31...@msgid.meganewsservers.com...

[Coyoteboy]

Jeff Strickland wrote:
> Also, the circuit operates on milivolts or some very low logic voltage like
> that. I don't really know or care, my point is, any problem with the
> connection points will translate into poor operation of the system.
>

Only the sensor side operates at low voltage (0-1.1v to be precise),
the heater side (that the error is) is 12v and fairly high current.