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Oxygen Sensor Heater Circuit; Code PO141 on 2000 Metro 1.3 Automatic
Topic Started: Jan 2 2010, 05:39 PM (3,832 Views)
cckelleyiii
New Member
[ *  * ]
Anyone have any ideas for me?

I'm new to the forum. I have a 2000 Metro Lxi, 1.3 Automatic. Driven daily.

CEL was on and the code was PO141 - O2 Heater Circuit. In the fall I had replaced the entire exhaust and put in a generic four-wire sensor.

I checked resistance on the heater wires of this sensor and had an open circuit. The new sensor that I had (same generic type) showed 3ohms on my meter. I installed the new sensor, erased the code and assumed fixed on 12/31/09. Today I had the CEL and same code again!

Any ideas on what might fry this little heater so quickly?

Also, this is the rear O2 sensor. If I understand right, it doesn't come on unless the car is going 50 mph. How much voltage does the ECM send to this heater and how can the voltage to it be tested, etc.?

Help! Any thoughts? :hmm
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Murf 59
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Welcome to the forum. I am no help on this one. But someone will be around who has the anwsers. Hes Mr Wizard LOL Sorry I got carried away.
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cckelleyiii
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Thanks for the encouraging word :)
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Bad Bent
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Facetious Educated Donkey

Yes, welcome to the forum, cckelleyiii! :coffee

I'm of no help either. :shake :shake

My source, www.obd-codes.com/p0141 says;
Causes
A code P0141 may mean that one or more of the following has happened:
* open or short to ground in the wiring harness
* O2 heater circuit wiring high resistance
* O2 heater element resistance is high
* Internal short or open in the heater element
Note: Typically a failed catalytic converter does not cause this code. You're more likely to see a P0420 code for a failed converter.
Possible Solutions
* Replace oxygen sensor (cannot repair open or short that occurs internally to sensor)
* Repair short or open or high resistance in wiring harness or harness connectors
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mwebb
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FOG

lesson learned by you

do not use generic 02 sensors

another lesson as of yet unlearned
DO NOT USE ohm meters on cars - the results are useless
any test results from UNloaded circuits may not be accurate and will result in need less tail chasing ...
===============================
anyway
white wires are heater wires
one gets 12 volts positive or system voltage from Fuel pump relay / main injection relay
the other gets ground , 12 volts negative
at the pleasure of MR ECM , yes , after 50 mph has been crossed on my 1996 10G

so
what is measured voltage to your rear 02 sensor heater after you reach 50mph BEFORE you switch off the key at hot idle
?

see the "how to" about T pins in connectors before proceeding
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cckelleyiii
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Hey thanks Bad Bent and mwebb!

Mwebb, pardon the ignorance of a amateur shadetree mechanic. How do I fool my car into thinking it's going 50mph? :hmm

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mwebb
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FOG

cckelleyiii
Jan 3 2010, 04:47 PM
Hey thanks Bad Bent and mwebb!

Mwebb, pardon the ignorance of a amateur shadetree mechanic. How do I fool my car into thinking it's going 50mph? :hmm

how about , just drive the car at 50 mph
once the system has switched the rear 02 sensor heater circuit to on
it stays on

until you switch the key to off
so after you get to 50 mph
let the engine idle and then
test the rear 02 sensor heater circuit

post results here
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cckelleyiii
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Thanks mwebb, I didn't know it would stay on.

I got 13.8 volts on the heater wires using the t-pins. I think I saw in a manual several years ago for a previous car that they called this backprobing.

Great idea and good explanation on the guide that you wrote. :rocker

Turned the key & engine off - no voltage. Out of curiosity turned the key on and had 11.9 volts (27 deg. outside). I turned the key off and started the engine again - 13.8 volts again. Turn off the car and turn the key on again - 11.9 volts again.

I thought it was supposed to be off until 50 mph? :-/ Or does the warm engine keep the thing ready to go back online right away for awhile?



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mwebb
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FOG

..."Turned the key & engine off - no voltage. Out of curiosity turned the key on and had 11.9 volts (27 deg. outside). I turned the key off and started the engine again - 13.8 volts again. Turn off the car and turn the key on again - 11.9 volts again. "...

i did not know a hot engine is a criteria which would allow the rear 02 sensor heater to be powered up after crossing the 50mph threshold after the key was cycled .... good to know ....
=====================================================
those values should be consistent ...
to see which side the problem is on

you will need to measure voltage drops on the rear 02 sensor heater ,
a simple task my dear departed mom could do with her good hand tied behind her back
blindfolded.

DVOM positive test lead to battery positive , negative test lead to rear 02 sensor heater POSITIVE side
engine running after exceeding 50mph , hot engine
what is the value ____________? cycle key a few times , does the value change or is it constant ?


DVOM negative test lead to battery negative , positive test lead to rear 02 sensor heater NEGATIVE side
engine running after exceeding 50mph , hot engine
what is the value ____________? cycle key a few times , does the value change or is it constant ?

both value should be UNDER 200mv and should remain constant
post test results
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cckelleyiii
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Okay, I don't have a very sensitive DVOM. It's one with a clamp-on ampmeter that works well for larger currents, A/C etc.

But...I did get .1 to .2 vdc(toggling back and forth) to the + lead and -.0 (neg. sign toggling on & off) on the neg. side.

Isn't that way too much drop, or do I need a more sensitive meter?

It's a balmy 19deg. :cold At least I'm out of the wind chill!
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mwebb
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FOG

100 to 200mv is too high

but on a 02 sensor heater circuit , should not affect the functioning of the heater

your rear 02 sensor is bad -

do not use a FRED's part
===============================================================
and your alternator may be doing something too ,
try measuring voltage on the battery with the engine at hot idle
with and without all loads switched on

you can measure across the battery using AC volts as well , if there is ripple or AC voltage present above about 2 to 500 mv or .2 to .5 volts
the diodes in the alternator are in trouble
they may not act up until they are loaded or hot
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cckelleyiii
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Readings on the battery at hot idle: :type

No loads, headlights on automatically, everything else off - 14.1-14.2 vdc, 0 vac

All loads on - 13.0-13.1 vdc, 0 vac

I think it's pretty normal for 12 volt system to be going over that a bit with the alt. running :dunno

So did both these O2 Sensors go bad because they are generic? Do you think there's another problem?

Is a universal senor okay, just use one from a reputable company like denso or bosch?

Hey, thanks for all the help with this!



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Johnny Mullet
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Fear the Mullet

I never use "universal" parts myself. They only cause problems down the road. I messed around with 02 sensor wiring before also. Apparently, yours has an internal problem. There are basically 4 wires.

2) heater wires
2) signal wires

As long as the wiring is good and not shorted anywhere, this code (heater circuit) should not come up with a good sensor and a good circuit. You can follow both 02 sensor circuits easily by tracing the wires. They end up at the passenger strut tower. Carefully double check the wiring and connectors and if they check out, get a good 02 sensor. This car saves you money on gas, don't cheap out on fixing it.
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mwebb
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FOG

cckelleyiii
Jan 6 2010, 05:55 PM
Readings on the battery at hot idle: :type

No loads, headlights on automatically, everything else off - 14.1-14.2 vdc, 0 vac

All loads on - 13.0-13.1 vdc, 0 vac

I think it's pretty normal for 12 volt system to be going over that a bit with the alt. running :dunno

So did both these O2 Sensors go bad because they are generic? Do you think there's another problem?

Is a universal senor okay, just use one from a reputable company like denso or bosch?

Hey, thanks for all the help with this!



i dunno why the "universal" parts fail so regularly
i suspect it has something to do with what they say in the Bronx

you can not polish a turd
but that is not true , you can if you dip it in liquid nitrogen ....
but even if you do , what do you have when you finish .....?

be aware that a 6 inch drop to concrete will kill an 02 sensor , even a new
OEM part
or
squirting oil or coolant or penetrating oil on the thimble OR
the 02 sensor body can also kill it
deader than dog poop

and
if you solder a signal wire connection on a FRED's 02 sensor
you block the path for atmospheric reference and
not kill the 02 sensor but render it NON functional .
=====================
regarding your charging system voltages under load
http://geometroforum.com/topic/2716924/1/#new
read the 2nd post in that thread -
if you have a mind to
perform the test and post results
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cckelleyiii
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I haven't tried the voltage testing under load.

I did resolve the problem!

I did read on another thread where Johnny Mullet said the purpose of the rear sensor was to keep tabs on the cat. converter. :news

Well...this car has a brand new one because the old one rusted out and I replaced it. So I figured that perhaps I should just attach another universal sensor that I had lying around - trust me it's the last one I have! and just strap it up by the firewall. I figured the heater element in these universals just couldn't handle the exhaust heat. I didn't want to spend $90 on a drop in 02 replacement just to have it burn up also. Not that it would, but...

No smog tests here in good ole Indiana and I've never ever had a cat plug up or cause a problem on any car I've had. They all seem to rust out first!

Week and a half, no codes and car running great. :thumb

I'm ready to try some of those gas mileage mods I been reading up on! Right now I'm doing 32-33 mpg, 1.3, 4cyl, 3 spd auto. It tops out at 36 mpg in the summer w/o mods. I wish it were a freakin' 5 manual - way not enough gears. :rasp

Thanks mwebb and Johnny for the help!
cckelleyiii
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