HELP! 2000 ford focus SE p0141 code

this code say problem with HO2S post cat. heater circuit itself. Maybe sensor is aftermarket, there is problem with heater circuit. Could be sensor itself, wiring, ECM.

The sensor is aftermarket. It's an bosch sensor from autozone. It has been a nightmare with this car. It coded p0141. I replaced the post car sensor. Did not clear the problem. Further research showed the catalytic convertor was failing. Had that replaced. Car coded for BOTH o2 sensors, fouled cylinder 4, and running too lean bank 1. I replaced plugs and wires. Cleared codes. Checked again, car coded p0135, pre-cat o2 sensor. Replaced the pre-cat o2 sensor. Cleared computer. Car coded again for p0141 post cat sensor. Replaced the sensor again today. Drove the car almost 20 miles, took it back to inspection and while waiting in line, the light came back on again. Checked codes again, p0141 post cat sensor. The car is also running rediculously rough at an idle. Stalls at stop lights. Seems to run fine at speed, but at an idle, it will stall. It did NOT do this before I replaced the catalytic convertor. I'm at a loss at this point.

Throw the bosch 02 sensor away and buy the correct part from your local ford dealer and check for that split pcv hose that all those cars seem to have going from the pcv valve to the throttle body!

pin 1 and 2 (two white wire or same colour wires) at lambda sensor is a heater circuit and should be approximately 7.5 ohm, pin 1 should be battery positive. Green-yellow wire is coming from fuse box fuse18 10A to pre cat. O2 sensor (you should have battery positive there). O2 sensor post cat. is connected via green-blue wire to wire above by junction somewhere. Also on this wire you should have battery positive. Check if you have got battery positive on this two wires. Check what voltage you have got between this two wires (green-yellow and green-blue), should be not more then 0.2V while engine running and hot.

PCV hose usually cause fuel trim too lean, by the way you can check, there are common fault.

This is my girlfriends car, and I am tracking down old issues that were never appropriately addressed. She had a "rough idle" problem about 3 years ago. So, I was digging around under the hood tonight and found the PCV valve had been removed from the valve cover and electrical taped to block it, and the corresponding hole in the valve cover was left wide open. Additionally, I found that the EGR Valve Pressure Sensor REF port hose that runs to the EGR valve was disconnected and left hanging. I reconnected both. The idle is better, but it still surges and fluctuates and threatens to stall if you don't hit the accelerator. I will be replacing the PCV and hose and investigating the EGR valve as it appears someone beat the crap out of the top of the housing with a hammer. The question is this: Could these obvious vaccumm issues be causing false readings on the O2 sensor?

Not at O2 heater circuit. O2 sensor have inside two separate circuit, first one is for ECM emission reading, second one is heater circuit inside O2 sensor. P0141 is heater circuit in post cat. O2 sensor. You have got sensor itself faulty, or wiring or ECM. Please check fuse no18 10A for power supply maybe dose not give right voltage to O2 sensor. If you put volt meter across battery positive and pin1 heater circuit on O2 sensor you should have no more then 0.2V reading, do this test on each sensor, it will mean you have got good voltage supply to each sensor. Do this volt test while engine running and hot, this is important, circuit has to be on LOAD.

Thanks Peter. I appreciate the help. She cannot afford to replace this car, and this thing has been driving me bonkers! We ran the car for well over an hour last night. Ran it to operating temperature several times. Started and stopped the engine several times. Could not get the computer to code. She ran it the 12 miles or so to work today, and still no check engine light. We will run it throughout the weekend (won't be able to get it to NJ inspection again until Tuesday morning anyway because of the weekend and holiday on Monday) and see how it performs. The PCV valve is definitely shot, when I pull the valve it has positive suction, which I'm told is indicative of PCV valve failure. But that is literally a $10 part, and since it has been just laying in the engine compartment for probably about 3 years, I will replace that regardless. But if the car does not code again, then it seems the problem has either self corrected or has corrected as a result of several other cascading issues. If the car does code, I will break out the volt meter and follow your instructions for testing voltage to the sensor. That is realistically the only other thing I can come up that would potentially be the problem. One additional point to note: While climbing under the car, I was presented with a MASSIVE oil leak. The oil filter was loose, so I took it to a buddy at a shop who did an oil change for me (considering he only charged me $20 to do an oil change, I wasn't going to bother with it myself, wasn't worth it). It is STILL leaking actively. To the tune of about a quart since the oil change was done just 6 days ago. (I am praying it is the oil pan gasket and not the engine seal.) That being said, the wiring harness leading to the rear o2 sensor was SATURATED in oil. Is it possible that this oil leak is causing the issue? When she gets it home today, once it cools, I will climb back under and hit the connections with cleaner, let them dry, and regrease the two electrical sockets, reconnect, wrap in tape, and see what happens from there just to be safe. (this car has made me love my old chevy truck more and more with each passing day!)

Oil should not effect wiring, dose effect electric boards (chips), but not wiring. By this "Could not get the computer to code" you means could not read engine codes or no code present?

Peter-atip wrote: Oil should not effect wiring, dose effect electric boards (chips), but not wiring. By this "Could not get the computer to code" you means could not read engine codes or no code present? I meant no code appeared, check engine light did not come on.

uhm oil will affect wiring! Especially in an 02 sensor as most 02's have to breathe through the sensors wiring! It's how some sample the air around the pipe as a reference! It's why dielectric should never be used on an 02's connector! It's the same effect that older silicone gasket maker had on 02's! If oil leaking onto wiring didn't have an effect then why do oil pressure sensor connectors often turn the oil check bulb on when tey leak and short across the terminals! Oil will conduct so that's why it shouldn't be in a sensor connector! Not to mention what an oil leak onto a harness will do to the wiring's insulation! Lets try and keep info posted on here as accurate as possible!

Just wanted to thank everyone for their input and help. This car really had me baffled. BUT. After correcting the vaccuum issues, AND cleaning the wire harness and connector on the sensor, the computer has not thrown a code yet. Not exactly sure what corrected the problem, I am guessing it was a combination of things, but it seems to be ok, and it's running a heck of a lot better now. True test will be Tuesday morning when we run it through NJ inspection yet again. Again, thank you to everyone that chimed in and offered assistance!

Here's your problem I believe". It sounds to me like it is your "Mass Airflow Sensor" which is easly located between your airfilter box and the intake manifold on top of the engine. You can't miss it". There is one wire assembly connected to it. You can buy a new one for $99.00 or do what I did and take it off, and spray carberator cleaner on the little metal wire you see inside it. "DON'T TOUCH THE WIRE". Spray it heavly 2 or 3 times and let it air dry. It gets a build up uf crap on it and gives the computer a false signal as to how much gas to give with the air. That's causing the terrible idle and stalling".

57KEVY wrote: Here's your problem I believe". It sounds to me like it is your "Mass Airflow Sensor" which is easly located between your airfilter box and the intake manifold on top of the engine. You can't miss it". There is one wire assembly connected to it. You can buy a new one for $99.00 or do what I did and take it off, and spray carberator cleaner on the little metal wire you see inside it. "DON'T TOUCH THE WIRE". Spray it heavly 2 or 3 times and let it air dry. It gets a build up uf crap on it and gives the computer a false signal as to how much gas to give with the air. That's causing the terrible idle and stalling". Thanks. I'll look into that as far as the rough idle is concerned. I don't know that that is causing the issue with the O2 sensor, which cropped up AGAIN on Sunday on her way to work. 2 days with no light, and then POOF, the light is BACK on again. I'm about to junk this thing and call it a loss!