Check Engine Light

Tiny
LEV1017
  • MEMBER
  • FORD TAURUS
I have a 2000 Taurus wagon with the 3.0 DOHC V6 Duratec engine. I bought it used last year and It has 138,000 miles on it.
About a month ago, the transmission started giving me problems by not shifting when the engine was cold. I took it to a local transmission shop and it was diagnosed to be the speed sensor, which was replaced for $350. I thought this was a bit steep, but I paid the bill and was on my way.
The next day, I was on my way to work, when the 'Check Engine" icon lit up. This had never happened since I bought the car 14,000 miles ago, so I went back the the repair shop, thinking maybe they neglected to connect everything back.
The mechanic ran the diagnostics and the codes P0172 & P0175 [System Too Rich (Banks 1&2)] showed up. He thought it was my O2 sensors, but he didn't see anything physically amiss. He reset the codes and said it could be a glitch in the system and if it came back, he'd investigate further. By the way, the original problem was corrected - it shifts normally now.
A couple days later, the 'Check Engine' icon came on again, so I decided to take it in for a thorough diagnostic checkup at a reputable engine specialist in my town. He ran it through the diagnostics and reported that the P0172 code popped up, further explaining that the O2 sensor was switching slowly, causing the icon to be tripped.
He said that it would cost between $300 and $600 to replace the sensors and that his advise was to just ignore the 'Check Engine' icon, that it wouldn't be detrimental to my engine. He did suggest running a couple tanks of gas with injector cleaner in it, he reset the code, & I was on my way.
Well, about three days later, the dreaded icon came on again! Now my questions (finally!).

1) Do you think it could be just a coincidence that the icon illuminated right after trans work was completed or could the trans shop have caused it? They stated that they dropped the trans for the speed sensor repair, but didn't disconnect the exhaust.
2) Why would the icon not come back on immediately? As I stated, it would stay off for a couple days before reappearing.
3) Is the price I received ($300-600) reasonable to replace the sensor(s)? How many sensors are we talking about, which ones should be changed, and where exacxtly are they located? Can a mechanically-inclined person (me) change it/them or are there special tools/skills needed to complete the repair?
4) Or should I just take the last mechanic's advise and learn to live with a constantly lit 'Check Engine' icon?

One last note - the engine's performance doesn't seem to be affected by the icon being lit, but I did read that when it is lit, the engine's computer runs a 'limp program' that decreases gas mileage and increases emissions. Because of this, when the icon reappears every couple days, I disconnect the battery for a few minutes, which resets the code and the icon disappears for 2-3 days.

Sorry for being so lengthy, but I figure too much info is better than not enough! Edit at will! And thanks.
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Wednesday, September 12th, 2007 AT 7:32 PM

5 Replies

Tiny
SERVICE WRITER
  • EXPERT
Post is not too lenthy, but informative and necessary. Thank-you.

The tranny shop sounds like they did good. The second Specialist shop scares me. You do not ignore the CEL. Ever. An intermittant problem and such can be trying and all, but it needs to be addressed.

While it is technically, possibly true damage is not going to happen to the engine it may affect other systems and your fuel miliage. I am not confident with their response.

Your first question is hard to answer, mostley becasue we don;t know the true cause yet. Maybe they did, maybe they didn't cause it. Since it went a week, I am more inclined to think they didn't cause it or it would have happened within a day. The harness may have been placed in a position that it may be damaged and causing part of the problem.

2-The particular self test may not runn right away. Self-tests or monitors sometimes run in sequence or the vehicle needs to be driven in a prticular way to make the test run. If it fails, it throws the light.

3-We can cross that bridge later and provide help if needbe.

4-Hell, no!

First thing I would try is to get some electrical cleaner spray froma parts store and clean the Mass Air Flow sensor.
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Wednesday, September 12th, 2007 AT 7:48 PM
Tiny
BMRFIXIT
  • EXPERT
HI
1 I DONT THINK THEY ARE THE CAUSE OF YOUR PROBLEM SPEED SENSOR DOSNT REQUIRE TRANNY REMOVAL ON YOU CAR

2 ECM RUN A CHECK ON THE SYSTEM EVRY SO OFTEN CONDITIONS HAVE TOBE MEAT BEFORE THE ECM GET READY SO THAT TAKE TIME DEPAND ON THE DRIVING YOU DO MAY BE UP TO 50 MILES
3 MAY BE IF THEY FIX IT WRIGHT 600 BIT HI
4 NO NO NO NO

CHECK : YOUR FUEL REGULATOR
MAS AIR SENSOR
COOLANT
COOLANT SENSOR
THERMOSTATE
HIGHL UNLIKLY ITS THE O2 SENSOR

GOOD LUCK

[
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Wednesday, September 12th, 2007 AT 9:01 PM
Tiny
LEV1017
  • MEMBER
Paul, I had said that the idiot light came on the day after the transmission shop completed the repair, not a week later, but anyway, I inspected and cleaned the Mass Air Flow sensor as you suggested and reset the CEL 2 days ago - the icon came back on today. Now what? Should I replace the MAF sensor? In reference to my question #3:

Is the price estimate I received ($300-600) reasonable to replace the O2 sensors? How many sensors are we talking about, which ones should be changed, and where exacxtly are they located? Can a mechanically-inclined person (me) change it/them or are there special tools/skills needed to complete the repair?

Thanks.
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Friday, September 14th, 2007 AT 6:37 PM
Tiny
SERVICE WRITER
  • EXPERT
I'll update this shortly, but here is somthing from another mod:
Having spent many years "under the hoods" of countless cars and trucks, I've had the opportunity to note quite a
few common vehicle problems. I've seen many DIY repair folks struggle to diagnose their cars and trucks. This will
be another continuing series in DIY Auto Repair. Hopefully, some of these problems, tips and fixes will help you to
quickly and accurately diagnose and repair your car or truck!

A recurring P0171 and P0174, System Too Lean Banks 1 & 2, have been a common problem with the Ford 4.0L
engines (VIN Code "E", Plastic Intakes) Not only are there recurring codes, other symptoms may include, stalling
when hot or cold, rough or erratic idle, excessive fuel consumption and misfire codes may also be present.
(P0300-306)

Common Causes:

1. The most common cause is the failure of the seals between the upper and lower intake assemblies. Resulting in a
gross vacuum leak, causing the above symptoms. Some very quick and easy ways to diagnose this issue are:

a) With a can of Carburetor Cleaner, spray around the mating surfaces of the upper and lower intakes. (Please use
caution while spraying! Do Not spray on hot exhaust manifolds!) If the idle "settles out" or increases there is a leak
at that point and the seals should be changed.

B) If you have a scan tool and can view O2 data stream then use the same procedure and "view" the O2's as you
spray. You should note that they both will go "fixed rich" for a short time. Indicating a leak at the seals.

2. The second most common cause, and this is not limited to the 4.0 engine, is a contaminated Mass Air Flow Sensor
or a M.A.F. That has failed completely (A good portion of the time it will not set a code!)

a) A quick fix for this is to remove the M.A.F and with some electrical cleaner or isopropyl and Q-tips, gently clean the
small coiled wires inside the M.A.F. If this does not cure the symptoms, then further testing is required.

Though there are other causes for these symptoms, these are the 2 most common. Additionally, it has been a trend
that the upstream O2 sensors fail when the vehicle is above 100k miles. They will usually not set a fault code and
can cause a wide variety of symptoms similar to the ones earlier described. Other symptoms may also be P0172,
P0175, Bank 1&2 System Too Rich.

Until Next Time

Chris
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Saturday, September 15th, 2007 AT 7:45 AM
Tiny
SERVICE WRITER
  • EXPERT
The price for the O2 sensor replacement sounds reasonable. Keep in mind your paying for not only labor and parts but an additional mark up on the part by the shop...Which is necessary for them to sta in business. IF your going after them, the front two would be the ones I would expect.

You'll need an oxygen sensor socket to replace them. Without knowing you and your capabilities or having the car in front of me I don't know how easy this would be for you. You'll certainly stand to save a fair amount of money if you can.
DON'T BUY UNIVERSAL SENSORS.


http://www.2carpros.com/forum/automotive_pictures/30961_o2loc_1.jpg



The O2 sensors produce a waveform pattern that can be evaluated with a quality scan tool, if the shop did this on their recommendation of the sensors replacement, then it would be a fair guess.
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Saturday, September 15th, 2007 AT 8:26 AM

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