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Topic Index > Repair and Maintenance > Sordid Tale of a "Service Engine" Light

Sordid Tale of a "Service Engine" Light

There's a lot to my sordid tale so I'm going to try to be as brief and concise as possible:

Car Info:

1998 Ford Taurus station wagon V6 3.0L DOHC

"Service Engine Soon" light is ON. 140k miles. New spark plugs and air filter. Oil changed last week. Engine tune up and transmission flush about 3 months ago.

Got car inspected: FAIL.

Error Codes:

P0135 - O2 Sensor Heater Circuit (Bank 1 Sensor 1)

P0155 - O2 Sensor Heater Circuit (Bank 2 Sensor 1)

P1131 - P11XX Manufacturer Controlled Fuel and Air Metering (aka mass air flow sensor)

The Service Engine Soon light is ON. I live in NC. While visiting parents in VA last weekend went to their trusted mechanic. He replaced the two O2 sensors. I drove the car a few miles and the SEL came back on. Sent it back to mechanic. Mechanic had hell of a time finding the problem, some kind of "tree" test (this is a monroe muffler) and it pointed towards the O2 sensors again. He replaced all 5 O2 sensors including the first two he replaced (for free, he's a great guy). In the end I think he forgot to do anything about the mass air flow sensor. At that point I had to go home to NC but on the way the SEL came back on. Took it to an inspection place and they kindly read the codes, all three original codes were still present. Guy looked under the hood and showed me that one of the air lines is ruptured. Went to Advanced Auto Parts and got new hose, attached it, disconnected battery for a bit. Next day after about 20 miles the SEL came back on.

All the while I've been told that the engine is running rich and that can screw up sensors. My question is this, can 150+ miles of driving with new O2 sensors and a ruptured air line (don't' know what the line is called, it is not very big or long) ruin my new O2 sensors? Frustrated, I bought all new sensors including the mass air flow one to try to resolve this on my own but I don't want to ruin these sensors as well. Also I've read varying opinions on how to clean them (petrol, blow torch, etc.).

Thoughts? Opinions? Thank you in advance!

-matthew

Wow! A LOT of expensive guessing going on! Don't change those new parts. You'll still have a chance to take them back to the store. All of these circuits, which contain sensors, can, and should, be tested CORRECTLY. So far, you've not had that. No.

In the DTC (Diagnostic Trouble Codes), P1131 through PXXXX doesn't indicate the MAF (Mass Air Flow) sensor to me (I could be wrong........or, right).

My DTC look-up says, for P1131, "Lack of H2OS11 Switches--Sensor Indicates Lean (See P2195"

P2195, "O2 Sensor Stuck Lean, Bank 1, Sensor 1"

You need someone who really understands these systems ------ beyond being able to read a code reader.

Updated: 07/17/2008 10:54:02 AM

Thanks hellokit!

Are you insinuating a dealership? I've been at my present location for about two years and I've yet to find someone I trust. I pour over reviews online of different mechanics, but I've never walked away happy... It's gotten to the point that I'm going to start trying to repair everything I have the tools for myself. I just bought ramps yesterday, next purchase will be a specific repair manual.

After you purchase the items you described I would recommend you buy a good scan tool, go to class & brush up on your electrical dianostic skills and prepare yourself for a whole lot of head scracthing & headaches (don't forget to also get some advil). Simply put todays cars are not as simple to work on as they used to be. Without a decent scan tool I wouldn't work on them myself. A code reader cannot tell you if the part sensors are working or not. Stick with a decent mechanic whom thinks he shouldn't charge more than 3 hrs for what he just spent 10 hrs to fix and you will come out way ahead. Just show some compassion when he apologizes for snap on not making a crystal ball so the fix would have been much quicker.

My guess is look for a leak in the exhaust somewhere upstream of the o2 sensors that are giving the error. The oxygen sensors detect if there's oxygen in the exhaust due to incomplete combustion-- but if there's oxygen leaking into the exhaust between the cylinders and the o2 sensors it'll tell the computer that the mixture is lean and try to adjust the mixture to compensate. When it doesn't address the issue, it'll trigger the codes you've listed. Try popping open the hood and, have an assistant hold something over the tail pipe (a hand with a thick glove perhaps) and listen for an exhaust leak somewhere near the exhaust manifold on the engine or some of the more forward pipes.

How long can I safely cover the tail pipe without messing something up?

A stretch of hose is a great way to locate exhaust leaks and pinpoint odd sounds. 3 feet of garden hose will do nicely. Stick one end in your ear and move the other end around suspect areas, kinda like a stethoscope. Caution: DO NOT tangle you or your apparatus with belts or rotating parts!

Word of mouth can often find the best person for a given problem. Ask around of people who have had emissions coded problems.

Read this Ford service Article No. 98-23-10, dated 11-23-1998. It's still pertinent. Its title is, "Mass Air Flow (MAF) Sensor Contamination Service Tip". A spray can of MAF cleaner (available from auto parts stores) may solve some of the problems.

Thanks, I'll get the MAF cleaner tonight.

Back to my original question for a second though, could the ruptured air line have screwed up my sensors to the point where even after repairing the line, the new sensors would still be showing errors?

Since you've got the 2 O2 circuit codes, it could'nt hurt to take a quick look at the O2 circuit fuse.

The fuse list in your owners manual will probably show this as the "HEGO system" fuse.

The P-1131 is a perfect match for the
ruptured hose that you replaced.
If the hose was sucking air, it would certainly cause that lean code.

The new sensors should still be fine, I would'nt replace them.

Thank you so much, everyone, I really appreciate everyone's help.

So, it is sounding like if the MAF is bad/dirty/bad fuse, then that could be throwing off the O2 sensors that are giving errors? I was going to ask earlier, but it didn't seem logical to me.

I'll second 87 Ranger about checking the fuses. Since you have a failed heater circuit on 2 O2 sensors that is more than likely the problem and I also agree any new O2s will be fine.

Absolutely ignore any comments made by Shakespirit; the resident troll whose knowledge of automotbiles is far less than zero and continues to prove it on a daily basis. The advice he's been dishing out here actually belongs here.

http://www...zlG28B-R8Y

98 Taurus Manual (fuses page: 111) http://www...manual.htm

I do not see a fuse listed "HEGO system" anywhere in the manual. I do see a fuse for "Heated Oxygen Sensors, Canister Vent" (mini fuse)...

I'm going to try following the steps on this nice looking forum thread on cleaning the MAF sensor: http://www....php?t=563

Yep,thats the one to check. If it's blown it explains the P0135 & P0155 codes.

Alright. I just finished cleaning the MAF sensor with the MAF sensor spray, I'll have to wait until tomorrow to test it out. Unfortunately, the sensor (wire thingys) did not look dirty to me... I used a clean cloth to wipe the dust from the inside of everything anyways (without touching the sensor). I DID, however, see some black, oily substance below the round metal plate with the hole in it leading into the engine. I wiped that up too. Air filter is still clean as a whistle.

I checked the fuse, it was fine. I held the tailpipe ends and listened under the hood, but didn't hear anything obvious.

I DID see another air line that was cracked at the ends, so I went ahead and replaced it, but it was probably not leaking...

If your car has flex fuel capability, it has fuse #28 for the common power to ALL four O2 heaters. They are not individually fused. If the car isn't flex fuel capable, the fuse will be the main power fuse for the ECM (engine computer).

You (or, a mechanic) need the specific instructions for checking the O2 heater voltages to the O2s and on to the computer terminals. Or, be able to read and understand the wiring diagrams.

Power is provided to the O2 heater elements, for a couple of minuets,when the engine is cold, and just started. The O2 heater ground sides go to the ECM terminals. The ECM grounds each one (making current flow through the heaters) just long enough to heat the O2s to operating temperature. Then, it opens each circuit and current flow stops (and O2 heating element heating stops).

Updated: 07/17/2008 11:54:13 PM

You have reached my choice of car disposal points. 140,000 miles is when I get rid of a Taurus. No particular reason; I just wouldn't keep on maintaining it.

Well, 15 miles to work and the CEL did not come back on... but then again it didn't come back on last time until my drive home from work... so we'll see then. Either way, I will probably go back to Advance Auto Parts to have the codes read again and cleared if they exist.
I'm going to be doing more research and digesting your last post, hellokit, thanks again (and no, the car is not flex fuel capable).

RE: pleasedodgevan, I want to keep my Taurus because it is a station wagon and I do a lot of home repair, so it is convenient for hauling large things inside and I have had very few problems with it. That said, within the next year or two I do want to supplement it by buying an electric car for my day-to-day commutes.

Updated: 07/18/2008 08:46:09 AM

The CEL DID come back on... So I guess at this point I"m convinced that it's not the sensors or a leak... damn because those would have been easy...

Don't assume they are the same codes (they may be). Get them read.

Several things can contaminate MAFs and oxygen sensors: silicone from ArmourAll; Son of a Gun; silicone in potting compound from the connector of the MAF, itself; some spray electrical contact cleaners contain silicone; RTV sealant used as gasket or sealer. If any of these products are used near the air intake to the filter (the air intake could be near a tire, or the bumper), the silicone could be drawn into the MAF. That gooey stuff you saw may be potting compound containing silicone.

Please read the Ford service bulletin Article No. 98-23-10, dated 11-23-1998 Mass Air Flow Sensor Contamiation Service Tip. You'll find it in Technical Service Bulletins and Recalls, section Electronic Devics, Computers, PROMS, Sensors. The article outlines how to determine if the MAF is faulty, or not.

Clean the MAF, again. Look for that gooey stuff, and spray and clean it.

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Sordid Tale of a "Service Engine" Light