Auto Scanner pays off.

[publius]

Today, the idiot light ("check engine") went off on my '01 Crown Vic today. I thought it seemed to be running a little off before.

For those of you who like to do your own mechanickin', a scanner to read the darn computer's diagnostic codes is a must have. I bought one a couple of years ago, and it's paid off. I went and got a good one, that can read live data, and played with that for a while (tells you all the operating data -- air flow, fuel trim, manifold pressure, timing advance, etc, etc.).

Well, the code on the old girl was "P0401: EGR flow insufficient". Without a scan tool, you'd be lost as to what could be wrong, and at the mercy of a shop, or worse, a dealer. :lol:

The EGR valve itself was working fine. Trouble was this DPFE sensor (Differential Pressure Flow EGR). The supply pipe has a little orifice and the thing measures the pressure drop to determine EGR flow. That sensor went bad, making the thing open up the EGR too much, hence the poor running, and it finally went so bad, it tripped a fault and threw the idiot light.

That was $40 part and about 20 minutes of work and she seems to be running okay now. Again, you can't do without one of these scan tools these days.

-Richard

[novaderrik]

if you didn't have a scanner, you could always talk to a friendly mechanic at a local shop that works on every kind of car, and they'd be able to tell you what the different symptoms mean in different kinds of cars.
or find a website dedicated to your kind of car and hope there are some real mechanical types on there that know what they are talking about..
if i have any questions regarding pretty much any kind of car or truck, i head to www.chevelles.com and ask away. it's a site dedicated to 64-72 Chevrolet Chevelles, but they will tackle ANY automotive problem on any kind of car.

[mfumbesi]

Without the scanner you will only have the idiot light ("check engine") and your mechanic friend/forum will not be able to help you. When the idiot light ("check engine") comes on it can be any thing, so the scanner is still a good idea.

[darkhunter]

If you're doing you own work, a scanner definitaly pays off--when you make the repair, you can use the scanner to clear the codes from the computer. Otherwise, it's the old disconnect the battery and wait 15 minutes deal, which has the side effect of clearing everything so your engine has to relearn it all.

[Moose]

Thinkgeek has these neat scanners you can mount on your dash (multiple colors, of course). It interfaces with the standard port for this sort of thing, and can read, reset, and write to supposedly any car's computer (after 1994 when the interface was standardized) and a few from earlier times.

When my corolla gets a bit older and I have some cash to throw, I may get one.

[publius]

if you didn't have a scanner, you could always talk to a friendly mechanic at a local shop that works on every kind of car, and they'd be able to tell you what the different symptoms mean in different kinds of cars.
or find a website dedicated to your kind of car and hope there are some real mechanical types on there that know what they are talking about..
if i have any questions regarding pretty much any kind of car or truck, i head to www.chevelles.com and ask away. it's a site dedicated to 64-72 Chevrolet Chevelles, but they will tackle ANY automotive problem on any kind of car.

You see that's just the thing. The days of diagnosing problems from symptoms are over. And they've been over for a while. The computer control system is becomming so complicated, more and more every year, that you have to have a scanner so the computer can tell you what it thinks (*thinks* mind you) is wrong. And then you start.

A symptom such as "hesitates when accelerating" could be a thousand different things. Experience may tell a mechanic who works on various models what it is likely to be, but it's no guarantee. For example some particular model might be known to have some sensor or other part fail and that usually produces a given symptom. But you don't know. And I can't stand the philosophy that some have of just replacing parts until you stumble on the bad one.

The idiot light just means "the computer thinks something is wrong".

-Richard

[Neverfly]

On older vehicles, if you insert the key into the ignition and turn it to "on" (not start) then to off, three times in succession then leave it on, the check engine light will then blink out a numerical code. You then look up what the code means in the back of your owners guide and viola- diagnostic.
Not always perfectly accurate but then even the best scanner wont perfectly tell you the exact problem every time. But it does tell you were to start.
I don't know if that trick still works on todays newfangled cars:p

[hhEb09'1]

You'd think there'd be some sort of auto auto scanner

[novaderrik]

Without the scanner you will only have the idiot light ("check engine") and your mechanic friend/forum will not be able to help you. When the idiot light ("check engine") comes on it can be any thing, so the scanner is still a good idea.
not true. once you get past all the extra wires and sensors, there is still an internal combustion engine in there somewhere. give me a little time with any car, and i can narrow most problems down to one of a few things as good as or better than the guys at the stealership that only know how to plug in their $5000 scanner.
sometimes, those scanners can make you replace a bunch of stuff that has nothing to do with the root cause. unless, of course, you have the factory flowcharts that show what it means if this code is shown with this other code when the car is doing either this or this..

[publius]

Okay. Take what just happened in my OP. You've got a car with the idiot light on. It sort of ran a little off before it came on. That's all the information you have. What do you do and where do you start without benefit of a scanner to tell you what the system is complaining about?

Yes, there is an internal combustion engine under there. However, rather than being controlled by simple mechanical systems, it is now controlled by a complex computer system that relies heavily on a vast array of input and output sensors that tell the computer the instantaneous operating conditions of the engine.

The reason for that is primarily emission control, but better performance when they can squeeze it in, has been a nice side effect. Priority is emissions, fuel economy, engine life, and performance, in that order. Emissions trump all. As emissions requirements get stricter, that system gets more and more complex.

My '04 F-150 doesn't even have a mechanical throttle control anymore. It's fly by wire. The gas pedal simply connects to a sensor (actually two for redunancy that must agree) that tells the computer how much oomph the operator is requesting. It then decides how much to open the actual throttle plate via a servor control. Scared the heck out me, but after reading up on it I was sastified there was no more chance of failure than that of a regular mechanical linkage. They added parallel "sanity check" routines that watch what the main routines are doing.

The idiot light on my '92 F-150 came on intermittantly a while back. Code was "lean limit reached", which meant the computer, trying to maintain "stoke", had reached the limit of the fuel "trim" on the injector on the lean side. That is, it kept getting "rick" feedback, and went way past a programmed limit on how far it can lean back on the injector pulse. The systemr realized something was out of whack somewhere, and tripped the idiot light.

The scanner is only the beginning there, for certain. :) But tell me, without a scanner, what are you going to do there? Oh, the O2 sensor was fine.

-Richard

[phaishazamkhan]

not true. once you get past all the extra wires and sensors, there is still an internal combustion engine in there somewhere. give me a little time with any car, and i can narrow most problems down to one of a few things as good as or better than the guys at the stealership that only know how to plug in their $5000 scanner.
sometimes, those scanners can make you replace a bunch of stuff that has nothing to do with the root cause. unless, of course, you have the factory flowcharts that show what it means if this code is shown with this other code when the car is doing either this or this..

QFT, when I purchased my first car I discovered that it didn't have a gas cap. Being an idiot I drove around without the gas cap after the discovery and the idiot light came on. Went to a nearby dealership because they were near my work and I wouldn't have to bum rides or miss work.
They told me that the oxygen sensors were bad and then they sold me a gas cap for six bucks. Three hundred and twelve dollars and two years later I discovered the issue was the idiot light needed to be reset after replacing the gas cap.

[publius]

Ah, yes, that's the dreaded enhanced "EVAP" system that checks for leaks and will throw the idiot light if the gas cap is not sealed. That is one thing I dread, EVAP problems.


EVAP is short for the evaporative emissions control system. Gasoline is volatile and slowly evaporates, especially in a fuel tank in a hot car. These raw hydrocarbon vapors are a scourge that is destroying the planet and probably killing millions of people per year, you see, and so they had to prevent those vapors from escaping.

First generation solution was simply to seal the tank and hook up a charcoal canister to absord the vapors. When the engine was cruising, you opened up a purge valve to let the engine suck the vapors out of the cannister.

But the deadly vapors still escaped, and so the system had to become more and more complicated. This kind of stuff is mandated by people who've never had to work on anything, nor even get their hands dirty probably. And so a persnickety leak detection system had to be added, which uses vacuum and or pressure changes to determine if the system is leaking. IIRC, it's now down to the equivalent of a .020" hole. The system must detect and flag a leak that small.

It's a royal you-know-what when it fails.

And even with all that, the biggest remaining source of the deadly vapors is during refueling. So they're mandating crap to try to minimize that.

-Richard

[novaderrik]

Okay. Take what just happened in my OP. You've got a car with the idiot light on. It sort of ran a little off before it came on. That's all the information you have. What do you do and where do you start without benefit of a scanner to tell you what the system is complaining about?

Yes, there is an internal combustion engine under there. However, rather than being controlled by simple mechanical systems, it is now controlled by a complex computer system that relies heavily on a vast array of input and output sensors that tell the computer the instantaneous operating conditions of the engine.


The scanner is only the beginning there, for certain. :) But tell me, without a scanner, what are you going to do there? Oh, the O2 sensor was fine.

-Richard
it depends by what you mean by running a little "off"..
if it idles rough and kind of stumbles like it has a constant vacuum leak, the first place to look is at the egr valve. well, after checking that all vacuum lines are in good shape and plugged in. first, i'd unplug the egr valve and see if it runs any different. then, maybe i'd tap it with the trusty "Ford tool " (you might call it a hammer, but a wrench works just as well) to see if it "fixes" itself. then i trace the "path" leading to the egr valve and see where it takes me.
one thing about egr valves and the switches that operate them- they rarely go bad. but they do get chunks of carbon in them holding them open, resulting in a constant big vacuum leak that makes it run really lean- and, to compensate, the ecm tells the injectors to throw in more fuel, which causes a surge and a big loss in fuel economy and drivability.. pull off the valve, clean it, and put in a $5 gasket from NAPA that has a screen to prevent it from happening again. but most people-and shops- go straight for the expensive fix and replace the egr valve, which "fixes" the problem until another chunk of carbon gets dislodged and takes up residence in the egr valve. it might be a day or it might be a year, but it will probably happen again if it happened once. some engines are worse than others- like, for instance, the Vortec 4.3 V6 in my 92 AWD Astro van. they are known to "eat" egr valves, but in reality, it's just a small piece of carbon getting in there that takes 10 minutes and the aforementioned $5 gasket to fix.
one other thing to check on your car is that crappy plastic intake manifold- they are known to crack and cause a huge vacuum and/or coolant leak, but all the code reader is going to tell you is that it is running lean for some reason and the ecm is trying to compensate by putting in more fuel.

[novaderrik]

and, for the record, i'm not against getting a scanner. but don't trust it as the final word in what's wrong with your car. i know plenty of people that have wasted a lot of time and a lot of money "fixing" what the scanner said was the problem, only to find out that it was something simple. and some of these people were good mechanics that put more trust in the little scanner they bought at Wal Mart when a little mechanical common sense would have told them what was wrong.
but it can be handy to have sometimes.

[publius]

I did not say a scanner tells you what the problem is. I said it tells you what the computer sees wrong. This thing here is out of whack. That circuit there is out of range. Without that, you're looking for a needle in the haystack. Knowing what fault the computer is seeing helps you narrow that down.

And yes, there are idiots, especially at these big box parts store that will read your code and sell you whatever part is closest to whatever code is read. That is not what anyone with any sense will do.

Now, in the case of my Crown Vic, the scanner told me the computer was complaing that the EGR flow was insufficient. That is, it was thinking it wasn't getting enough flow. By running a little off, it was just sort of flat cruising and opening the throttle. It was that way for a couple of days, and then it threw the light.

That result told me I need to think about why the system would think the EGR wasn't flowing. First off, it could be it wasn't really flowing. So, I manually opened the valve with a vacuum pump, heard the engine stumble. The PCM was able to compensate and keep it running, which surprised me.

That verified the EGR was not plugged, and also explained the flat running. It was opening it up too much, thinking the flow was lower than it really was.

The next culprit was then the flow sensor itself, the DPFE unit. I took that off, blew some air through the hoses to the EGR pipe to verify they were opened. Then it was time to check the DPFE sensor by applying a pressure differential and seeing if the signal output behaved as expected.

It did not. Ergo, DPFE sensor is bad. Went to parts store, bought new DPFE sensor and problem solved.

And my point is, without a scan tool, where the heck would you be there? Doing nothing but scratching your head and taking guess at a million different possibilities.

-Richard

[novaderrik]

actually, i'm better at actually "fixing" a car in person than explaining what i might do over the internet. if you know each engine design's inherent quirks, you know where to start. sometimes a code reader will get you there, sometimes not even close.
you seem to have a good analytical way of going about diagnosing and repairing things- which puts you a couple steps above the average "tech" at most new car stealerships that went to a couple of years of tech school to learn how to plug in a scanner and replace parts on the customer's dime.
had you taken it to a Ford dealer, you might have gotten lucky and had a person working on it that's seen it a hundred times and knew that particular switch was a problem, or you might have gotten a guy that saw the "egr flow low" code and started off by throwing an egr valve at the problem- at your expense, of course- and when that didn't fix it maybe the proper part would have been thrown at it. but you'd be out at least a few hundred $$$ in parts and labor due to his laziness and ignorance.
this is why i think more people should take the time to at least learn the basics of what goes on under that hood that they barely know how to open. if nothing else, you can be armed with the basic knowledge to know when they are trying to screw you over.