Sordid Tale of a "Service Engine" Light

Maintenance/Repairs
, ,
261

Good question, I would think that the scan tool records data once a second… So the distance between each circle (or triangle, or square, etc.) on a line might represent a second (and the distance between each X tick mark might be one second)… I cannot figure it out based on the manual: http://www.harborfreight.com/manuals/98000-98999/98614.pdf I guess if I timed how long a recording session takes (it records 60 “frames”) and divide that by how many frames it records, that would get me the answer.

Note that for the graph you cite, the car was not shifting properly again and thus the RPMs where much higher than they should have been. If that matters…

262

Oh, so you think that my results may not being showing that anything is wrong, because I did not do the tests while the car was moving at 30 and 50mph. Am I understanding you correctly? You don’t have to respond if I have that right.

263

Air flow is different when the engine is under load (moving the car at speeds). See, above for later post (out of chrono order).

264

Well, Autozone has screwed me. PCM didn’t come today either.

265

hellokit,

In regards to your previous post updated on 09/19/2008 11:09:15 AM:

Firstly, I think the scan tool records data approximately one every 3 seconds… It graphs live data faster than that, but it doesn’t save the graphs.

For kicks, here are today’s codes, freezeframe:

Control Module
$10 SAE J1850 PWM
Stored Codes
P0135 O2 Sensor Heater Circuit Bank 1 Sensor 1
P0155 O2 Sensor Heater Circuit Bank 2 Sensor 1

Control Module
$10 SAE J1850 PWM
Pending Codes
P0708 Transmission Range Sensor A Circuit High
P0455 Evaporative Emission System Leak Detected (large leak)

Control Module
$10 SAE J1850 PWM
View Freeze Frame
DTCFRZF P0155
FUELSYS1 CL
FUELSYS2 N/A
LOAD_PCT(%) 56.1
ETC(?C) 87
SHRTFT1(%) 1.6
LONGFT1(%) 0.8
SHRTFT2(%) 0.8
LONGFT2(%) 0.0
RPM(/min) 1718
VSS(km/h) 71

Now on to the tests (I will keep updating this post):

With the car on, engine off, the TPS held stead at 18% for about the first 40 seconds. Then it jumped up to 20.5 for about 2 seconds, and went back down to 20 were it remained for 30 seconds. Then it dropped to 18% for the rest of the test, which lasts about 3 minutes.

EDIT
Here is a graph of the MAF(g/s) and RPMs based on the test that hellokit requested. Remember to LEFT CLICK on the graph to make it BIGGER: http://badsushi.net/images/98taurus_livedata_19sep08.jpg

–

I have figured out that the scan tool simply records data as fast as it can. So, if I told it to record EVERYTHING, then it would take about 3 seconds to record 1 bit of data from each sensor/gauge. If I tell the tool to record data from just one or two sensors, then it records an entire set of data (60 frames) much faster. Maybe there’s nothing it can do about that, maybe some sensors only spit out a reading every couple seconds, while others every second?

266

Your car, Taurus LX, 3.0L, DOHC has a significant VIN S. You have to order the MAF sensor using VIN S to identify the correct MAF sensor for your car; but, install the replacement PCM, and test it, first, before ordering.
Your MAF sensor may be ok. The resistance of the PCM for the light blue/red Sensor Input has to correspond to a resistance in the MAF sensor. Together, the MAF sensor and the PCM drop the voltage by 12 volts (7.5 volts drop by the MAF sensor, and 4.5 volts drop (the remainder) by the PCM).

I think the PCM may have the wrong resistance. So, you need the replacement PCM to find out for sure.

267

Your graph of the MAF sensor http://badsushi.net/images/98taurus_livedata_19sep08.jpg shows air flow (in grams/seconds) which are about twice the values as my reference values from the alldata charts.
The alldata charts show expected values of 4 to 4.5 g/s at hot idle (700 rpm), and 11 to 13 g/s at 2500 rpm. The graph shows 8 g/s, and 19 g/s, respectively.
The error could be in several places: the alldata charts; the graph; the output signal from the MAF. The measured voltage (1 volt), at the MAF Sensor Input, is wrong (should be 4.5 volts, plus), and that will negate the values of the output indications. So, that supply voltage has to be fixed, first (see prior post).

268

So, I just got off the phone talking to Ken Gamble from The Driving Lane radio show (http://www.northhillsauto.com/) live on the radio. I’d like to thank Ken Gamble for that opportunity, I really appreciated it.

Here is what I got out of our conversation:

  1. I really should spring for Ford authorized parts. My O2 sensors may be Bosch, but his experience is that they can be lazy.

  2. He and the director of training for his shop agree that a faulty MAF sensor CAN be influencing my O2 heaters.

So based on that and hellokits latest posts, today I will trade in the MAF sensor I bought, that doesn’t fit my car, for the appropriate one (and install it before I leave the store) and drive it around a good bit this weekend.

I wish I could take Kens advice about Ford authorized parts, but unfortunately I simply cannot afford them right now. Remember that PCM I’m still waiting on? It will end up costing $115.00. When I called a Ford dealership to ask for a price, they wanted %500.00. I don’t want to think how much everything else must cost through them…

269

For the nth time, I’m not convinced that the MAF Sensor is faulty. It has the wrong input reference voltage; so, that is causing the wrong output voltage signal. The PCM is causing the wrong input voltage. So, I’m NOT voting for a faulty MAF Sensor. See what difference the replacement PCM makes before convicting the MAF Sensor, ok?

EDIT
There is NO proof for either position. The MAF Sensor resistance, between the red wire pin and the light blue/red wire pin, should be a certain value. I don’t know that required value; nor the MEASURED value. The PCM resistance, between pin 88 and pins 103 (et al.) should be a certain value. Again, I have neither, the required value, nor, the MEASURED value.
If one did have those ohm values, they would be, about, 70% for the MAF Sensor, and 30% for the PCM, of the whole. Add the ohms of the MAF Sensor to the ohms of the PCM, and you have the whole (or, total) for that circuit.
Right now, those percentages (ratios), of resistances, are: 92% in the MAF Sensor, and 8% in the PCM . Which one has the right value? No one knows.

270

OK hellokit, you have a better grasp of my situation than anyone, so I’ll follow your advice first. I just got my hopes up because I had to have everything fixed this weekend. But that’s not possible now because the PCM did not come in. In the meantime, just because I don’t have any other tests to do, I will try to follow the input wire in to the MAF back to the PCM to make sure there is not any physical damage on the wire.

If there is anything else I can do while I wait for the PCM, or just another way that I could display the data I’ve already posted to make it easier to decipher, let me know.

271

I agree with Hellokit. Wait to see what happens when you install the replacement PCM and drive around with it for a while. It seems that whenever you work on it something else changes status. Please don’t take that the wrong way, as I am not refering to your work when I say that.

As far as the MAF sensor having effect on the O2 heaters the only way I could see that happening is if the supply voltage to those sensors is caused a problem due to something wrong in the MAF sensor and we are not having a problem there, that I can see at least. If I remember correctly, the supply voltage is common to all those things from pin 15 of the PCM.

I think the PCM is supposed to supply the MAF either a regulated voltage or possibly a constant current to the sensor. Then as the airflow changes through the sensor and the resistance of the sensor changes with that, the changes in current are seen by the PCM and then it makes the fuel adjustments accordingly.

272

Make sure they have ordered the correct PCM…the one for VIN S, 3.0L DOHC, non-flex fuel application. Call’em.

273

Yes, I remember answering that question (correctly), but of course that doesn’t mean I have any confidence in them. When it does come in, I’m going to walk into the store with my old PCM and compare it to the new one, in the store, before walking out with it and installing it in the parking lot.

274

While you’re “jest twiddlin’ yore thums”, how about getting some resistance (ohms) readings on your old MAF Sensor, and the new (wrong) one. Measure, and record, the ohms across terminals A and B, A and C, B and C. Then, bring’em here. [Idle hands and all that.]

275

I admit, hellokit, I have not done that test yet… I will soon.

Maybe I’ll get the PCM today? I don’t know.

This morning my radio (original) started going in and out. As in, it would go mute for a couple minutes and then start working again. If I turned the radio off then on again, it would work for a bit. Change the channels, no difference. If I turned the speakers all the way up, I could not hear any hum or hiss from the speakers. I kind of saw this coming because a few months ago the radio started going silent while I was shifting from park to reverse or drive, it always does that now. Also, when I was parking I put it in reverse and the steering wheel tightened up as if there was something wrong with the battery. The dash showed the “low coolant” and seat belt lights illuminated. The lights went out when I put it in Drive. My seat belt was on at the time, and I’m pretty sure my coolant level is fine (I’ll check it it later).

SO, the only reason why I bring any of this up is I’m HOPING that this is further evidence that there is something wrong with my PCM and many things will be fixed once I get the new one. Maybe even my ABS light that comes on sometimes? Maybe the OD light that sometimes (rarely) comes on as well?

EDIT

Thursday. Thursday I have been promised my PCM.

276

Sorry Matthew, the PCM has nothing to do with the radio or warning lights turning on and off. They are due to a different electrical issue.

277

well that sucks

278

Go to the back of the repair manual. Look at the power distribution diagrams. Find each affected component and see if they share a common fuse. If they do, then, the problem is isolated to that one circuit. Then, it’s time for MR. Multimeter.

279

mfaerber,
I hadn’t forgotten about you; just got my own kettle of fish with a friend’s friend’s 1998 Ford. It has P0340 DTC (camshaft position sensor circuit gone to lunch) and other problems. I can apply some of the stuff I learned from “working” on your 1998 Ford Taurus, to it.

There is a Ford service bulletin: Article 98-23-12, dated 11/23/1998, which deals with P0705, P0708, and P1704. You said that your Taurus check engine light showed P0708, Yes?
The Article states that these DTCs “may be caused by the PCM, the wiring harness, the connectors, and/or the Digital Transmission Range Selector (DTRS)”. To troubleshoot it, you need the Ford scan tool (your scan tool may serve), and go to the PID table (included in the Article) and do some checks.

I’m leaning (to the left, about 25 degrees from the vertical) towards a wiring problem, considering the other problems.
While it’s dark, have able assistant sit in driver’s seat, with electrical power on, and radio powered on, sound muted, and shift through the gears, repeatedly. As aide is rowing the gears, look, and listen, into the engine compartment (keep under-hood light off), under the car, under the tranny and the engine. What you’re looking, and listening for, are little electrical sparks caused by electrical shorts. Continue with the rowing, and the looking, and the listening, as you use a stick to move wiring about. If you’re careful you can shake and wriggle wire harnesses and watch/listen for effects.
You may be able to read the Article through your public library. Here, it works by: going to the public library Web site; go to Electronic Databases; go to Database catagories: Reference; go to ARRC Auto Repair Reference Center. Ask a librarian for assistance.

280

Got my new PCM today. Big surprise, it didn’t work.

I changed out the old for the new PCM in the parking lot at Autozone. After installing it I went to turn the key. The car would not turn over. It would try to (“Ch-ch-ch-ch-ch”), but it was acting as if there was not any fuel in the lines. In the first key position, all the usual lights in the dash, and headlights, would turn on just fine. Checked the battery, it was fine. Removed the new PCM, then put it back in and tried again. Same result. Brought out a couple guys from the store, they had no idea. Brought the PCM back into the store to check the order and everything matched up (as in, they used the correct VIN number and one of the several numbers right on the PCM). I looked at their computer screen and they had the right car. One guy opened up the new PCM to make sure they didn’t need to switch out a chip (they did not) and said it smelled funny to him, and it shouldn’t smell at all. Then he said they are refurbs so his only guess was that I got lucky and got a bad one. I returned it.

So I’m pissed. At everything.

The whole “not turning over” thing, is that exactly what I would expect if the PCM was simply the wrong kind, or “flashed” with the wrong codes? I suspect so…

RE: hellokit,
Thanks, I’ll try that. Unfortunately, the only online car resource that my county library system provides is an online version Chiltons repair manual (which does include service bulletins). P0708 only ever came on once or twice. Last time I checked the codes (yesterday) I had P0135, P0155 and P0455 stored. No pending. And I had not worked on it for a few days.

The radio is getting worse, it usually does not stay on. Shifting is what effects it. In park it is fine, in reverse it is never on (which is something I noticed for the very first time after a mechanic worked on the car a few months ago… a hint?). In neutral it comes on. So, if I’m driving along with the radio on, and no sound is coming from the speakers, and I shift to neutral, sound will start coming out.

The low coolant light and seatbelt light are still coming on (at the same time) infrequently, usually right after I start the car, and at slow speeds. The steering wheel usually (always?) tightens up when they come on. All of my fluid levels are maxed.