Posts to, and from, the original post “Sordid Tale of a “Service Engine” Light” aren’t showing up on the board. Why? Technical glitch?
Huh? Did someone say something?
Dave S, you’re right. There is a lot of silence. To be specific, this is the post that I’m talking about: http://community.cartalk.com/posts/list/1326611.page Sordid Tale of a “Check Engine” Light .You may have to wait a few moments for it to load.
Sordid Tales…is about oxygen sensors and oxygen sensor heaters that defy diagnostics and a cure. A bad case of DTCs P0135, and P0155, just won’t stay fixed. The victim is a 1998 Ford Taurus Station Wagon SE with a 3.0L, V6, DOHC engine.
…A VERY SHORT RECAP:
…The Ford Taurus had intermittent problems of rough running, stalling, and DTCs of P0135 and P0155 for front oxygen sensor heaters. It had a couple of other DTCs (Diagnostic Trouble Codes) as well.
After exhaustive troubleshooting and inspection, it was determined that the Transmission Selector Sensor (aka the neutral safety switch), MAF (Mass Air Flow) Sensor, and both front and both rear oxygen sensors were bad. All of these parts were replaced with new parts.
The DTCs P0135, and P0155 for the front oxygen sensor heaters continue to come on. The scan tool reveals that all the oxygen sensors (front and rear) are operating properly except for the front two oxygen sensor heater circuits still set the DTCs P0135 and P0155.
Proper voltage (11.57 volts) was measured for all oxygen sensor heaters up to the PCM (engine computer) connector pins. The ground wires, from the PCM, tested good resistance values.
A replacement PCM (engine computer) was ordered and (finally) received; but, not yet installed because it’s Passive Anti-Theft System (PATS) hasn’t been programmed to recognize the original ignition key. So, the original PCM is being used to (attempt) find out where in the front oxygen sensor circuits the cause of the DTCs P0135 and P0155 truly is. If the orignal PCM isn’t really at fault, there will be no need to have its PATS reprogrammed and to change it out.
311 posts??? You guys still messing with this same car Hellokit???
transman
Thanks for this post hellokit. Yes… it’s my car… I’m working on it for the first time, ever, so it’s been a steep learning curve for me, to say the least.
Yeah, we’re still on this project and haven’t given up, but at least it is making some good progress now and think of the good info you have learned Matthew.
I also have had to repost some responses so I now copy them before sending them just in case.
When is the new PCM due in Matthew?
I got it, but it will not work until my “Passive Anti Theft System” module (a little chip in my key) is reprogrammed so that it matches the configuration of the new PCM. The new PCM HAS been flashed and it’s not one of those where you just switch the chips. So, the car will not turn over until the PATS module is taken care of.
Of course, I did not learn about any of this until after I installed the PCM and tried to start the car (it will not turn over because of PATS). I have since gone to google and learned about PATS.
Now, I have to spend between 60-100 dollars to reprogram or get a new key. I only have one key, which makes it complicated. Though, before I do that, I’m going to check the wiring (again?) for the O2 heaters.
Read some of the Web sites when you google: ford pats. One shows the steps to reset the PATS in a procedure which takes 46 minuets if the pcm is PATS I.
Some 1998 Taurus may have had PATS I PCM, others may be PATS II. How does one tell?
Another approach is to use a Ford PATS Remote Start Bypass Module which bypasses the PATS ($44): http://www.audiooutfitter.com/1100f/directed/p321256.html
Durn! Some people get to have all the fun!
Here’s a quote from an alldata article on Heated Oxygen Sensor: “An O2 sensor heater circuit fault is determined by [PCM] turning the heater on and off and looking for a corresponding change in the Output State Monitor and by [the PCM] measuring the current going through the heater circuit.” A fault will set "DTCs P0135, or P0141, or P0155, or P0161."
With these little tidbits in mind, if the common voltage/current for the front O2 sensors’ heaters has too much resistance (over a couple of ohms) the voltage AND current through the O2 sensor heater circuits will be lower…perhaps too low.
When you measure the red wire at the oxygen heater, the voltage should be very close (within a fraction of a volt) of battery voltage. If it’s not, resistance somewhere in the wiring / fuse between the battery and the O2 sensor is excessive (several ohms).
Someone (author unknown) is quoted in this forum: http://www.ford-trucks.com/forums/715534-p0135-and-p0155-codes.html that, “IF the PCM determines (based on coolant temperature [as reported by the engine coolant temperature sensor] that too much time elapsed before the oxygen sensor began operating properly, it will set P0135, P0etc.” How, and why, could too much time elapse? I’m not sure.
Anyway, make sure the engine warms quickly, past 160F degrees, without the engine cooling fans coming on, when the engine is yet too cool (less than 220F degrees). Make sure the engine thermostat is installed (some people remove the thermostat for some ignorant reason).
Here is an article which should help you in your understanding of OBD (On Board Diagnostic) Monitors: http://everything2.com/node/1685894
Why don’t you start a new thread, and call it Sordid Tale II. You can link it back to this one (Post not showing up. Why?), AND to the original thread Sordid Tale of a “Service Engine” Light. That way, every thing about your Sordid Tale can be kept in the same shoe box.
I know I’ve said this a few times before, but I think I found the problem and will now try to fix it.
Based on hellokit’s previous link, that contains this image: http://www.fordscorpio.co.uk/images/heatercirc.gif , I learned that the heater wires are spliced twice before going to the PCM. I had no idea what a splice would look like, but after a lot of rooting around under the hood, I found a splice that looks like the problem splice. Basically it’s a big black, plastic connector box with holes and pins. This particular box is right next to the battery. Several months ago I was having really bad problems with corrosion at the positive battery terminal. As a result, corrosion gunk went everywhere. Of course I checked the wires in the area, but I did not check this box because I did not know what it was and it’s so nondescript that I did not know how to look it up.
EDIT: I just opened it up and I think everything looks OK inside. The pins are covered in a slimy substance that is obviously supposed to be there. HOWEVER: Just before the wires go into the half of the connector closest to the firewall, they are completely exposed. Among those wires are a pure red wire that is ***** DAMAGED WITH COPPER EXPOSED ***** A grey wire with a black stripe is also damaged, but no copper. I will post pictures later.
Bingo?
If the wires aren’t touching anything else or each other and are making good contact then they are most likely ok.
We have been down this road numerious times already and to me you are wasting your time with further trouble shooting of the heater sensor circuit but that is just my opinion and it is your time. If you want to check out the heater wiring again remove the PCM connector then do a resistance check with one probe on pin 71 of the harness and to each of the pins 93,94,95, and 96 with the other probe. Hopefully all four of the readings will be around 10 ohms. This will verify the entire heater circuit of each sensor starting from the power side (pin 71) and the switched ground side of the PCM connector.
Well, that red wire was in really bad shape. There was a big chunk taken out of it and some of the strands of copper were corroded/damaged. I fixed that. Later tonight I will take the car out for a test drive.
If the CEL comes back on, I’ll whip out the multimeter again, tomorrow.
Well, if that wire is just tieing in the front O2 heaters you may have found the real trouble though other tests we made earlier indicated the PCM was at fault.
You may have found the power junction which serves the front oxygen sensor heaters. A wiring schematic is representational. The actual wire routing may be all over the place. I couldn’t tell you where the power junction is, just that there is one, and that it’s on the suspect list for causing a voltage / current drop.
If the battery was (is?) blowing battery acid, then, the battery case was (is) cracked, OR, the alternator was (is?) overcharging the battery…damaging the battery. Anything the battery acid came into contact with can be damaged.
If you haven’t started the repairs to the wires, you could do a voltage drop test to see what you have to start with (voltagewise) and then, later, to see what you have after repairs.
To check voltage, attach the multimeter negative probe to ground, and touch the positive probe to the battery positive post. Record value. Turn ignition switch to RUN (ON). Now, place red probe on that power junction. Record value. Backprobe each red wire at each front oxygen sensor connector. Record value. Backprobe the red/white wire (to PCM 93); then, the backprobe the white/black wire (to PCM 94). If you recorded these values before, wait until you do the repairs before making the measurements. It may be easier to frontprobe the PCM connector. The pin numbers, and locations will be the reverse, and backwards, of the PCM connector view you may have downloaded. So, be careful to check the correct ones.
We’re having fun, now, yes?
I allready fixed the wire…
The corrosion coming off of the battery is simply from the positive terminal, I do not think it is acid…? When I keep that red-spray-stuff on it, that green-blue gunk does not grow on the terminal. So, maybe it isn’t a big problem? The battery is only two years old.
Going out for test drive now. If the CEL is going to come back on, it WILL come back on after about 20 miles, as it always does.
EDIT
I just got back from a test drive. I drove the car to work and back. Total distance is about 25 miles. Historically, the CEL has ALWAYS come on after the first 20 miles. This time the CEL did NOT come on. There were no stored codes or pending codes. I’ll drive it more tomorrow.
Let’s hope that this time, you’ve got the critter.
Battery acid shouldn’t come from any post. Even a good battery will emit battery acid if the alternator is overcharging the battery. An overcharge voltage is a voltage over 15 volts; desired is 14 to 15 volts. A healthy battery (with the engine off) should have a voltage of 12.75 volts.
You can check the charge voltage, with your handy dandy multimeter, when the engine is running above 1,000 rpm. Excessive charge voltage usually requires replacement of the alternator, when the voltage regulator is built into the alternator. On some cars, the PCM regulates the charge voltage (controls the alternator voltage output).
uh oh, I think I’ve seen 14v before… I will check again
It sounds like you may have found the problem with the front O2 heaters this time Matthew, outstanding.
As far as the charging voltage goes 14 volts is no problem. As long the voltage goes no higher than 14.8 volts you are good to go.