MIL light on, two new codes on my 2000 Sable Vulcan OHV

O2 Sensors have heaters in them so they respond quicker when the engine is still cold. On Cold Engine Start, the sensors respond slowly to conditions that exist in the exhaust. On any given car, this does not matter, but on millions of cars it makes a big difference in emissions. This will not cause you any problems, except that it will annoy the smog technician.

There could be a blown fuse that is keeping the heaters off. It's unlikely that both sensors developed the same problem at the same time, therefore finding a common thread -- like a blown fuse -- is a smart first step.

It's P0, not PO, by the way.

P0 (zero) is a generic code that always means the same thing on all cars that produce it, P1 is a code that is unique to the automaker that produces it. The same P1 code can be produced by Ford and BMW, for example, but the meaning can be different because the code is defined by the automaker. A P0 code made by a Ford and a BMW would mean the same because it is defined by the OBD II conventions.

Do you know which fuses I should check? In my owner's manual, I am unable to find any fuses either in car or under hood for the sensors. Thanks.

I do not know which fuse you need to locate. There has to be one though. If the car has a secondary air pump, the same circuit that makes the pump come on with Cold Engine Start, and remain running for about 2 minutes, is the circuit that powers the O2 Heaters. The heaters are only on for a couple of minutes because the hot exhaust will make them hot. The heaters only shorten the time that the sensors need to work properly. If there was no heater element built into the sensor, the sensor would eventually be hot from the exhaust.

You can safely drive this car while you are sorting it out.

Alright, I'll take a look at the manual shortly. Thanks. There is one thing that has occurred to me, however. After I replaced the intake once I changed the plugs a few weeks back, I did forget to hook up a small harness that clips to the rear bottom side of the intake on this car (it's a green sliding clip). In reviewing the video I used to help me remove the manifold, the mechanic talks about this leading to the O2 sensors; I'll be me not clipping this back onto the manifold bottom has caused a short somewhere because that harness is just dangling in place.

The fuse involved is fuse&28, and I highly doubt the fuse is the problem because according to the owners manual, that appears to be a

HEGO Sensor, Transmission Shift Solenoid, Canister Vent, A/C Clutch Relay, Thermactor Bypass Solenoid If the fuse was bad the tranny wouldn't shift very well either and he'd be getting an evap code.

I do also get P1000 code, but I've had that ever since MIL reset 6 weeks ago. It did not fail inspection with this code.

I'll check that fuse later this morning just in case.

I can find very little, if any, change in terms of how it runs. I know nobody wants to hear this as I really pushed the issue the last time, but LTFT still run around +10. STFT do not and stay around 0.

I wish I knew for a fact where these sensors are located. I believe when I had the manifold off a few weeks ago, one of them was underneath the manifold between the engine and firewall. Not sure if this was the upstream sensor or not. I don't have much luck finding diagrams for the location and I'm also going to need a schematic I would think to check the voltages if I need to.

Thanks.

Leaving the plug disconnected could easily be the trouble. But it isn't a short, it's an open. If the connector leads to the O2 sensors, AND it is the power to them, then the fault conditions would be that the heaters do not turn on. A connector that is unplugged is the same as a fuse that's blown. You might not find any blown fuses because the problem is really an unplugged connector.

Sam, you must connect the plug that is hanging free. Nothing else matters until you plug everything back together. The O2 sensors are mounted to the exhaust system before the CATs. Typically the sensor is located where the manifold for 3 cylinders comes together. There is a sensor on each bank of cylinders, and there is a sensor before the CAT and after the CAT. The sensor before the CAT tells the computer to make small adjustments to the fuel trim, the sensor after the CAT only detects that what comes out of the CAT is cleaner than what went in.

Put your hand on the engine. Move your hand along the exhaust system until you come to an electrical device/connection. This is the upstream O2 Sensor -- it is before the CAT by the direction that the exhaust flows. Continue to follow the exhaust system over the CAT to the next electrical device/connection. This is the downstream O2 Sensor -- it is after the CAT by the direction that the exhaust flows. Some cars can have additional CATs, and there will be an O2 Sensor after any additional CATs, but I'm pretty sure your Taurus does not have any additional CATs, so the point is moot. I only mention it for the possible educational value in telling you that some cars have more than one CAT per exhaust bank.

The codes you are having, P0135 and P0155 tell you nothing about how well the sensors work, or do not work, they only tell you that the heater elements do not work. YOU told us they are not connected -- you left a connector unplugged -- and the computer does not know unplugged from blown fuse, so it is all the same to the computer.

Sorry to mislead, Jeff, but they are connected. What I was trying to say was that there is a plug and socket that I believe goes to the one O2 sensor, and this plug/socket "clip" to the bottom of the intake manifold. I did plug them back together when I did the spark plug job a few weeks back, but what I failed to do was slide the clip back onto the bottom of the manifold. So there is continuity, yes, I just didn't reattach the socket/plug combo to the manifold via its clip. So it has been this combo which has been dangling since I did the job. One of my suspicions is that since it wasn't reattached to anything to stop movement, that I now have an open or short in one of the wires. I plan to reattach this combination under the manifold, maybe replace a fuse, if one is blown, and reset the codes and see what happens.

I'm trying to follow you regarding sensor location but can I access this all from under the hood, or do I need to be under the car?

thanks

Whatever it takes. Open the hood and start from the top and go as far as you can, then crawl underneath and pick up where you left off. All cars are the same, so once you learn to identify the parts on your car, the next car might be a variant with respect to specific location, but it will be the same from a block diagram view.

The front half of the engine -- your engine is sidways in the engine bay -- is easy to follow, the other side is more difficult, but is still pretty easy.

When you open the hood and look down, you should see an exhaust manifold that connects three cylinders. You may or may not have the CAT visible -- on my BMW, the CATs can be seen easily, but on my F150 I have to get under the truck to see them -- and there is an O2 Sensor before the CAT and another one after. Depending on obstructions, you may or may not be able to reach the stuff you are looking for, and some of it might be blocked from view.

Frankly, if this is difficult then you should give pause to doing your own service else you risk introducing new problems. I appreciate that you want to fix your own car, but doing it over the interweb is perhaps not the best strategy. There is a certain amount of insight that you can only get from a guy, or gal, standing beside you pointing some of this stuff out. (Fixing your car is not out of the realm of female capability, so if you have a girl in your life that knows her way around a car, do not hesitate to ask for some help.)

Not that difficult, I just need guidance like that provided here and other forums. It really is appreciated.

What has made these problems bad for me is that they have all occurred during Winter and the Winter here has been very bad this year, mainly with extreme cold. Lacking a garage, all I have is a leaky carport with poor lighting so I've had to make sure to try working both at the 'heat' of the day and when lighting is best. If this were Spring/ Summer, there would have been a lot less issues.

Hopefully, once all the ice build up from yesterday thaws today, I can start the troubleshooting process. The first thing I want to do is reclip the sensor wire harness to the holding location on the manifold and run the fuse tests, then I'll go from there.

Not sure if this was you or someone else, but someone I thought said I could still drive the car this way, is that correct? Other than the codes, I don't see any abnormal readings on the scanner and the car seems to be running ok.

Sam

Well,I think I can stop my troubleshooting as I found the source of the problem. I suspected me not clipping the 02 sensor plug back onto the bottom of the manifold was the problem and it definitely is. Dangling there, the plug came up against something hot and was burned halfway through. It is a two part plug, green, four wires on each side going to the O2 sensors. Any idea what part this might be? In a pinch, I might be able to just clip off the plug on each side and splice the wires together if I color match them correctly. I can only hope that this short didn't burn out a sensor. Have yet to check the fuses, but will do so now with this info.

Not likely you burned out the sensor.

One issue with splicing is that the sensor is making millivolts of electricity at milliamps of current, this means that a defective splice can disrupt the circuit and prosent you with even more faults.

Since your fuel trim is calculated at least in part from the input from the sensor(s) and the trims change with the conditions, then it seems that the delicate part of the sensor is still connected. By the codes you report, it appears that all you took out is the control to the heater elements. By shorting the heater control to ground, you removed the heater signal from the sensor and it does not work. I'm concerned that you cannot identify a fuse for this circuit, but no matter. If all that's wrong is that the heaters are not working in the O2 Sensors, then you can safely drive this car without further damage -- assuming you capture the burned wires and prevent further damage there.

By having no heaters in the O2 Sensors you only cause them to perform slowly during the first two or three minutes of engine operation. The problem here is if that there are millions of cars all performing poorly during this time, then there is significant pollution being generated.

So today I cut out the connector and then spliced, soldered, heat shrinked and finally coated each connection with liquid electrical tape. I had some difficulty owing to the tight spacing, but did complete the job. I then tied this wire group to another wiring harness across from the manifold. Hopefully, that will suffice and no nasty overheating/ burning again.

I rechecked the fuse that Clare mentioned but it was good.

Driving cycle completed shortly afterward and no MIL light.

Hopefully this is solved now.

Do yourself a favor and go to a wrecking yard - a u-pull-it would be best, and buy the plug from a wreck of the same year and model - make suere the connector is green because there are more than one style of sensor/plug used on early 2000s Taurus and Sable and the plugs are not interchangeable. Remove the damaged plug and replace with the one from the wreckers. Solder and shrink tube the joint, then tape over that. Plug the O2 sensor into the new plug.

In retrospect, a U Pull It would have been ideal but there isn't one closer than 50 mi from me. The last one closed about 15 years ago.

I ran into the issue you mentioned when trying to order it online. I couldn't find the 'green' one and since it was melted on both sides, I probably would have had to cut off and replace the plug completely on the sensor side too. Rockauto, for example, had a brown connector on the harness side but no plug separately available on the sensor side. So a yard would have been best had one still been around.

Well, I think what I did worked out. I've never been a big fan of splicing where a connector was originally present, but if done correctly and thoroughly, 99% of the time it should suffice or at least I hope. Since the batt was unhooked while I did the splices, MIL reset and then I did a couple of driving cycles yesterday. No MIL after one deliberate cycle and then an additional 60 mi of driving. Hopefully problem solved.