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 Post subject: code P0140, please help
PostPosted: Thu Nov 19, 2009 6:05 pm 
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just installed new o2 sensors, both up and downstream, on ltb

now throwing a code 21, specifically P0140

might the distance between the 2 sensors be throwing the code? there about 3 feet apart, upstream is right behind head, and downstream is after the cat, but its a ways away due to the header length.....

needs to pass emissions ASAP.... any help would be awesome


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 Post subject: Re: code P0140, please help
PostPosted: Thu Nov 19, 2009 10:20 pm 
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P0140 Downstream O2 Sensor Stays On At Center
If you replaced the downstream O2 sensor, then obviously, it's the wiring.

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98 Sport Coupe Amethyst ATX to MTX swap (son's)
97 Expresso Coupe Black ATX stock (daughter's)
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http://forums.neons.org/viewtopic.php?f=3&t=402268


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 Post subject: Re: code P0140, please help
PostPosted: Fri Nov 20, 2009 2:20 am 
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ANYONE ELSE.... i still need help, please, if this has happend to you or you think its a distance issue, let me know thanks


Last edited by alpinegreenneon on Fri Nov 20, 2009 8:59 am, edited 1 time in total.
Extranneous off topic stuff removed


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 Post subject: Re: code P0140, please help
PostPosted: Fri Nov 20, 2009 6:59 am 
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The wiring or the connector from the O2 sensor connector to the PCM. The PCM is not getting the signal. The PCM is not capable of wireless input. Distance has nothing to do with the code.

Check PCM pin 7 on a '95 and PCM pin 51 on a '96 to '99, the TN/WT wire which is the signal wire for the downstream O2 sensor. Make sure there are no bent pins and that there is continuity from the O2 sensor connector to the PCM connector. Connect one lead from an ohmmeter to the the O2 sensor connector TN/WT wire and the other ohmmeter lead to the PCM connector TN/WT wire. Resistance should be less than 5 ohms. Also make sure the pinout in the connector has the TN/WT wire going to the black sensor wire, not to the grey(ground) or white (heater) sensor wires.
If all that checks out, the new downstream O2 sensor is DOA.

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Case

Image

98 Sport Coupe Alpine Green ATX stock
98 Sport Coupe Amethyst ATX to MTX swap (son's)
97 Expresso Coupe Black ATX stock (daughter's)
97 Sport Coupe Magenta ATX stock (wife's)
95 NYG ACR Coupe (restored to stock)
03 Dakota QC 4.7 4x4 ATX Patriot Blue stock

Can your key can be made from one of the free keys?
http://forums.neons.org/viewtopic.php?f=3&t=402268


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 Post subject: Re: code P0140, please help
PostPosted: Fri Nov 20, 2009 2:28 pm 
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wiring isnt an issue
and this just started after i put in the long tube headers
i had my mechanic check it out, he and another dodge mechanic are banking on the fact that the o2 sensors
which are normally close, are so far apart they arent reading the right a/f ratio, hence throwing a code

the code 12, p0140, comes on and off speraticly when i driver, it will stay on for a few minutes, go off, then come on again
reinforcing the fact that we think distance is an issue
im going to weld a bung lower and closer to my downstream o2 sensor, and see what happens from then


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 Post subject: Re: code P0140, please help
PostPosted: Fri Nov 20, 2009 11:43 pm 
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Can your scanner read the downstream O2 sensor voltage as the engine is running? Try wiggling wires and observe the voltage. Intermittant codes are almost always wiring.

From the Powertrain Diagnostics Manual (nothing here about distance from the upstream O2 sensor):
Set condition: If oxygen sensor volts stay between .29 and .72 for 30 seconds, the PCM pulls the sensor volts to 5.0 volts for 60 seconds and monitors the sensor voltage. If voltage stays at 5 volts, this trouble code will set indicating no activity.
Under possible causes, it lists open circuit in either the sensor or the ground wires or a defective sensor.

The downstream O2 sensor does not adjust fuel but rather measures cat efficiency. If cat efficiency deteriorates, the switch rate of the downstream O2 sensor approaches that of the upstream O2 sensor.

_________________
Case

Image

98 Sport Coupe Alpine Green ATX stock
98 Sport Coupe Amethyst ATX to MTX swap (son's)
97 Expresso Coupe Black ATX stock (daughter's)
97 Sport Coupe Magenta ATX stock (wife's)
95 NYG ACR Coupe (restored to stock)
03 Dakota QC 4.7 4x4 ATX Patriot Blue stock

Can your key can be made from one of the free keys?
http://forums.neons.org/viewtopic.php?f=3&t=402268


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 Post subject: Re: code P0140, please help
PostPosted: Sat Nov 21, 2009 1:42 am 
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i have a brand new cat on there, and yes i can check the voltage tomo morning, ill go to my shop and let ya know what i find out.. thanks!


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