Intermittent failues are such a pain


Back in the early '80s I worked in a metrology/repair shop and there was an oscilloscope that was 2+ time callback.
It was an early solid-state Tektronics, big and took the big plug-ins.
It would go to the customer, work for a minute and go dark.
Come to the shop and work fine for days.
Several other techs had spent a lot of bench time and could find nothing out of spec.
One day I was working on something, I forget what, but I checked the 120VAC supply at the socket and it was 109V, kind of low because we had a lot of gear running in there.
A little switch flipped in my head and I put that 'scope on a variac. At ~120V it went dark.
Check the power supply voltages, which lead me to a power transistor that was breaking down E to C like a zener.


Nothing stops you does it? Let me explain this for you. This was not a case of finding a solution on the Internet and obediently repeating it.

The Sienna Chat posting gave me three important technical data items. Those of you with Siennas will want to make a note of these.

  1. Sienna canisters have self-actuated valves.
  2. Those valves since not powered can get sticky.
  3. When they stick, you get intermittent evap failures.

As far as your sarcasm about finding something on the Internet, that doesn’t say much for this forum, does it? Over the years, I am confident this forum has helped hundreds, maybe thousands of people fix their cars, by finding it here on the Internet.

There are probably many people who come here with a search engine, find the solution to their problems, and never tell us. It is a great resource of data. But, no source of data can always deal effectively with intermittents.


A neighbor asked me to check his pickup out because it would veer slightly to the right on the highway. I found a worn outer tie rod end and followed the owner to a full service franchise tire store nearby to bring him home. When the service manager insisted that they do a 4 wheel allignment in order to determine the problem I choked back my smart azz answer and suggested that we shop around first. A sign on the door advertised 2 wheel alignment $59-4 wheel alignment $99. I wonder how many customers were robbed of $40 in that place? But the manager insisted that they must do the alignment to diagnose the problem. If only the public knew that all that is needed to set the rear end alignment on a solid axle vehicle is a tape measure. My friend does now. And the tire store lost a customer.


You folks are kinda getting me going. This is just so obvious, I don’t what there is to argue about? Some years ago my son stopped at Bobbie and Steves in Minneapolis Saturday night and his Pontiac wouldn’t start again (no starter sound). A guy there told him it sure seemed like the starter. At any rate, this is a pretty obvious problem 95% of the time so I drove up there Sunday and picked up a starter, then we went over there to have them put it in. B&S is one of the few places that have mechanics working on Sunday. At any rate the kid at the counter wanted to charge their standard $135 diagnostic fee or they couldn’t guarantee the work. We argued a little and I told him just put the starter in and I’ll take the chance on it not being the problem. It was the problem. Worked fine.

Now I understand both sides but why the heck would I pay $80 for a starter and another $135 to some kid to make sure its the starter, when its a pretty obvious repair 95% of the time?? Kinda like the tail wagging the dog. I’m the one paying.


Well, I’ll shake my own hand, because it was me who mad that comment. Well, I’ve got nothing to apologize for, and I stand by what I said.

There’s no “hand shake” emoji, so this will have to do.


Yeah, sure

With me, it’s all about inflating my own ego, NOT actually fixing anything. I probably have come backs each and every day. I probably couldn’t diagnose a flat tire. :crying_cat_face:

Seems you’ve got me all figured out

Let me pose a question to you . . .

If you already know what the problem is, why don’t you just buy the part yourself, install it, clear the codes, let the evap monitor run to completion. Drive the car under the exact circumstances in which the code would set, and THEN maybe you can say you know what the problem is, and you have proved it

Until then . . .

Sure, we understand each other just fine . . . whatever you say

As I said before, I respect you

But you apparently have no respect whatsoever for the mechanic profession

Seems to me you think you’re so much better than us “poor old grease monkeys”

Put your money where your mouth is and prove it

Get out of retirement, invest in tools and training, get hired somewhere. Then tell us how easy it is. Tell us about all the great experiences and/or run-ins you had with customers, management, etc.

It amuses me to no end . . . since I would theoretically refuse to work on your car, on YOUR terms . . . as would several of the other mechanics on this website, I might add . . . you are quite sure that also means I have no diagnostic skills, when it comes to intermittent problems

Glad you have everything figured out

You should sell these :crystal_ball: since you seem to possess at least one. You could make a fortune :thumbsup:

I just gave you a way to make a fortune . . . you should be thanking me :triumph:


In my earlier post about being sued and taken to court; I mention that because adhering to what a customer wanted is what led to that suit.

Customer comes in with an old air-cooled VW with the Auto-Stick. He wants the fluid changed (no pan or converter drain; only a resevoir tank) and mentioned the “shifting is balky”. I tell him the fluid is not likely the cause. The service manager (moron…) says to run it in and change the fluid.

Since I was the shop foreman and the techs were busy I brought this .2 hours job in and did it myself to keep it off the backs of the flat rate guys. Once done I did the usual; flagged the job under a tech’s number to help their check a bit by offsetting being screwed on warranty.
The trans was still balky and I told the car owner it was likely a problem with the electro-vacuum valve that controls the clutch operation.

Car owner balked at going any further and said “don’t worry about it” before leaving.
Three months later is when the deputy sheriff walked in the door with a handful of paper…

I could cite other examples of the same. This one was mentioned only because it wasted half a day of our time and half an hour of the court’s time.


Curious, what did the guy sue for and why?


He sued us “for ruining his transmission”.

His car was a mile away at an independent VW shop (well known for being shady) and the claim was that it was going to require 800 and some odd dollars down to the penny to fix it.
However, in court the car owner stated that the VW shop had barely looked at it and that the transmission was still in the car having never been removed or diassembled for inspection. We were the VW dealer of course.

The transmission itself was fine. The problem was in the electro-vacuum valve; a device called by different names.
The Auto-Stick cars had a clutch like a manual transmission but also a torque converter like an automatic. There is a set of contact points in the gearshift lever. When the driver is ready to shift the weight of the hand closes the points.
That in turn energizes the valve in the engine compartment and allows engine vacuum to operate the throwout bearing.

Most problems were due to vacuum leaks or the valve needing adjustment. The adjustments would control the harshness of the shift, release of the vacuum, and so on.
When the points in the gearshift lever burned (normal over time) this would also cause shifting difficulties. The usual fix for that was to remove the shifter and file the point surfaces.

When the guy first came to us he wanted fluid change only and refused to allow us to diagnose anything. Odds are any problem would have been cheap to fix. So he turned our original 25 dollar bill into a court case where he came off looking like a jackass. He was still arguing the point when the judge slammed the gavel and said enough.


Since the moron customer lost the case . . . did have to recoup the shop’s fees for appearing before the judge?

Or was his only punishment being forced to eat crow?

Boy, I wouldn’t be surprised if the guy’s wife made him sleep on the couch or in the garage for a LONG time after that

And she also probably told him “You’re a moron. I told you right from the start to just pay the dealer to diagnose and repair the car. But NOOOO, you don’t listen very well, do you?!”


Were you laughing when the judge slammed the gavel and the moron was still yapping away . . . ?!



And currently if they are a protected minority you could count on being sued for discrimination.


I have been wondering if you guys are fully aware of the enormity of what you have done on this thread.

There are going to be people reading this thread in the future. You guys might think everyone else, not a mechanic, is an idiot. But, they are not. They just don’t know mechanics, and mostly don’t want to know mechanics.

I said I was a Senior Technician with decades of experience on conceptually similar military self-test, and they will find it believable.

And, I also said I found a man who discovered what fixed that evap intermittent and why it did. They will also find it believable. He said there are non-powered valves in the canister that stick and cause the intermittent evap failure. Which is what the problem was.

And, very few car owners have not had the experience of paying for diagnostics for an intermittent with No Trouble Found. So, they are going to understand why I did not want to give it to a mechanic at great expense.

They are going to note that no one bothered to ask if it fixed it, and they will know this means you guys already knew it fixed it, which essentially means y’all well knew I knew what I was doing.

Yet, it didn’t matter to you whether I really knew what the problem was. It’s not just that you guys think customers are idiots, you obviously won’t tolerate any other type of customer. Your self-esteem comes before customer satisfaction.

What you have done is aid and abet and perpetuate the public stereotypes of mechanics. Good job, guys, please carry on.

You guys have to try to work with all sorts of customers. You have shared tales of Customers from Hell, and we believe those tales. You also in this era are going to have customers who really do know that is wrong with their car. Retired master mechanics with no access to hoist nor tools. (I had a neighbor like that in McAllen; he eventually died which happens a lot in retirement parks.) Senior Technicians. Car hobbyists. Automotive engineers who helped develop and maintain OBD but have no desire or time or tools to replace their canisters.

There aren’t many of them, we all know that, but they do exist and when they do come in the door you need to be able to work with them, rather then view them as the enemy.


customers like you are why there is a minimum diagnostic fee for shops. Yes, you may know what you are talking about, and have properly diagnosed the issue yourself, but for every “irlandes” that comes into a shop, there are 20 other “experts” that have no idea what is wrong with their car- other than what Dr. Google has told them. As mechanics, we have to deal with all types, and, unless we have an extensive history with a customer, no real way of differentiating between the experts and “the experts.”

So what do we do? We do our job as best as we can. We try to figure out what the problem is, and we try to fix it. Sometimes things get overlooked, or flat out missed, but I bet most of us save exponentially more time by doing our own diagnoses based on customer input, as opposed to if we just replaced what the customer told us to replace.

Not only does this save our time over the long run, but this also saves our reputation. Say Steve comes in and tells me that his starter is bad and to replace it, and that doesn’t fix the issue. Who’s gonna get the blame when Steve is talking to his friends? Not Steve, you can be assured of that. The shoddy mechanic down the road will get the brunt of the blame.
But if I check the starter, and save Steve some money by only replacing the needed relay (at a fraction of the cost,) who is gonna get the recommendation next time Steve hears about someone having starter issues? Yep. I may have gained a customer for life- all because I did my job right.

yes, irlandes- you were right about your 2002 Sienna. But you are a rarity in our field. But even so, customer input should be always taken into consideration when diagnosing- ESPECIALLY an intermittent issue. It can be so valuable.

but, if you came into my shop with the attitude you have displayed in this post- I’d politely ask you to go elsewhere. For exactly the situation that ok4450 shared. I don’t need that kind of customer causing me long term issues. I have a family to feed, and appreciative customers to take care of.


@eddo - Rather than click on the dumb heart button and just give you a like I would like to say you posted a very good reply to Irlandes. I wanted to but could not have done as well as you did.


you fixed it…give it up while you are ahead.


IMO irlandes does not personally have knowledge what fixed the evap problem

I carefully read can be summed up as thus

Some other guy told him what the problem is

irlandes did not diagnose it himself

he did not verify the repair, as per the factory service procedures

some other guy did all the legwork, and irlandes is accepting it as gospel truth

not quite the same as diagnosing, repairing, and VERIFYING the repair all by yourself

I have respect for everybody that took place in this discussion

But we all know some of us won’t see eye to eye


I don’t dislike irlandes, but I won’t agree with him on this particular subject

Some of the other guys I also don’t always agree with, but that doesn’t mean we hate each other

I don’t always agree with mountainbike and keith, but that doesn’t mean we hate each other

I might add something else

I’m not talking smack about engineers, scientists, etc.

But unless I missed something, irlandes did spend a LOT of time talking smack about mechanics

Perhaps he’ll dispute that and say it was directed solely at me

But that’s okay, because I have a thick skin . . . it’s a requirement if you want to survive in my business for any length of time

I’m not worried about some nameless and faceless person in cyberspace reading this and thinking that all mechanics are idiots

I’m not trying to win any new customers

I am done with this particular discussion

irlandes, I guess you can tell yourself you won by default or tko . . . whatever floats your boat



irlandes, I think you’re painting all mechanics as being callous, uncaring dolts and that is not the case.
I also do not think for one minute that all customers are idiots. Far from it.

In every shop that I’ve worked in we always went out of way to work with the customer; up to a point.

db4690, in regards to the guy who took us to court, he was still cursing under his breath when the gavel hit the bench.
Since I was the one doing most of the talking he gave me a dirty look. I just winked and smiled at him.
He started to fly off the handle and thought better of it.

All of that crap waste of time over 25 bucks which he was advised to not even spend in the first place.


Diagnosing intermittent problems is usually very time consuming. Generally factory warranty pays nothing and customer pay is limited to one hour of labor.

I have never rejected a customers request to replace a part, I have recommended to replace the actual failing part if it was apparent.

There are many occasions when a part is instructed to be replaced without diagnoses. Technical service bulletins, factory service actions, instructions from technical assistance and requests from management will instruct a part to be replaced. I wouldn’t object to replacing a part on a customers vehicle however I have suggested a more appropriate solution.

I have been employed as a diagnostic specialist and feel most of my co-workers need a lot more training and supervision, I see nothing wrong with a customers request to replace a part.


There are good mechanics and there are bad ones too. Same with doctors. I call them “the commoner”. The most common cause of chest pain in a 50 year old man is probably going to be heart attack, so if you treated them all as having a heart attack, then you are probably correct 9/10. The art part is finding the cause for the other 10%. Same goes for cars. I have had scenarios that I would tell a certain mechanic that I have already ruled out the most common causes (of lets say a “no start”) and at this point it is down to zebra’s. Quite a few I have dealt with, would try to charge me for changing a part I do not need (I have plenty of receipts to prove this). I am still okay with this, but the problem is when I go back because the problem was not fixed, they say now you have a “new” problem and charge me again for diagnosis and repair with no credit applied from the previous unnecessary repair.

On this forum, we have a gang of what I think very uniquely brilliant technicians that not only do a great job in their shops, but also provide a great free service for the rest of us. Unfortunately, the same can not be said for the average mechanic where I live.

If I had a shop and someone asked me to change a part that I wasn’t sure is needed, I would definitely have them sign a waiver.


I’ll be expelled if I give my full rant on doctors and the medical profession. They all too often want patients to believe they can walk on water but insist on demonstrating on Lake Superior in February. My local hospital has a monopoly on healthcare for a 5 county area and their staff nearly let me die of type 2 diabetes as they gave me tests for cancer, COPD, heart disease and various exotic blood disorders. I finally googled my symptoms and for less than $20 bought a glucose meter and found what the problem was. It was then that I realized the hospital’s business model was to begin with the most expensive tests first and work down to the least expensive regardless of the likelihood of successfully diagnosing the problem. Many shops find that strategy to be quite profitable.


My mom was in the hospital 2 days ago. high blood pressure dizzieness etc, the doc said the hospital is not a place you want to stay, cryptic remark, jst wondering if leaving yor car at a mchanic has any relevance.