A Mechanic's Life - Tales From Under the Hood

roadburner

Now that I'm working on the "inside" it's fun to observe what's happening in the service lane; my son has additional insights since he's working in the same place as a valet for the summer. So far I've only had two "My car's BT isn't working." issues and in both cases the client had accidentally turned their phone's BT off....

Mr_Shiftright

Are we sure customers REALLY want to see this?

stever

Well, not everyone I suppose, but I'd enjoy the updates.

Had more dental work today and I got to see the x-rays and photos that the guy takes. It's a real gadget office and I like gadgets so it made the experience smoother, if not actually enjoyable. They mill the crowns in house and you can watch that process if you like.

Being visible like this helps your customers understand a bit more about the work and why it costs what it costs.

The auto techs may need to keep the audio muted and invest in a blood filter....

Mr_Shiftright

I had that machine beamed on me some month ago. It shows you a picture of your skull and teeth. The tech said to me: "See, this is what you'll look like when you're dead".

Cheery guy.

stever

"When your mechanic took my console out, he found $100 bill and brought it to me in the waiting room. I misplaced that $100 last year and did not know where it was." (link)

Guess it's time to list all the rings and other stuff found by mechanics when they work on someone's car. Not sure if I want to hear some of the gore stories though.

thecardoc3

There has been more than one time that something in someone's car cost me my lunch.

Mr_Shiftright

I found a dead squirrel in one old truck I bought.

qbrozen

I had the opposite experience. After having a remote start installed on one of my wife's vehicles years ago, I found a test light.

Mr_Shiftright

That's a good find. That reminded me of another--I found a nice 17mm Snap-On wrench firmly stuck on a suspension bolt in a really tight place. Still have it!

qbrozen

Also a good score.

thecardoc3

Mr_Shiftright said:

That's a good find. That reminded me of another--I found a nice 17mm Snap-On wrench firmly stuck on a suspension bolt in a really tight place. Still have it!

I can't imagine keeping a tool like that. But then, I won't let a cashier give me the wrong change in my favor either.

Mr_Shiftright

I had no choice. It was a used car I bought from a charity. I had no idea whose wrench it was.

But I know whose wrench it is now

thecardoc3

My first set of Snap-On wrenches cost as much as my weeks take home pay at the time. Granted I made payments on them for two months, but for just 10 wrenches they literally cost half a day's take home pay a-piece.

I still have them although a couple are not the originals. If you try hard enough, even they can be broken.

Mr_Shiftright

I have a question. I always thought that if a 4X4 didn't have locking hubs, then the front driveshaft and front axle shafts will turn while in 2WD. But then I dimly remembered (or did I?) that some GM systems overcame this with some sort of actuator ???? Or did I make all this up?

I presume my 1998 Dodge Dakota does turn the front half shafts while in 2wd.

thecardoc3

I'm not totally sure what you are referring to. If the car does not have some type of a locking hub, then the shafts would be splined to the wheel hub and turn all of the time. GM does have an actuator that disengages the right hand axle shaft from the differential which serve to reduce 4WD drag, but the outer half of the shaft would still be turning with the wheel.

Mr_Shiftright

Sorry I was unclear there. On a truck without locking hubs and with manual engagement of 4X4, if the truck is in 2WD, will the front half shafts turn? Seems like they'd have to, in this case.

thecardoc3

If the axle shafts are not disengaged from the hub with a lock in device, then at the least the outer half of the axle shaft will turn with the wheel.

thecardoc3

This is already diagnosed and repaired but will shared here as an example of just what it takes to perform diagnostics on a system like this. The vehicle demonstrated is a 2008 Chevrolet Silverado HD2500 with the 6.6l diesel.
The customer reported a service park assist message on the instrument cluster and the Red LED comes on and stays on. Testing started by pulling trouble codes and the system responded with the B0958-01. Service information reports that as Sensor #1 (left rear outer) signal shorted to battery.

Part of a solid diagnostic routine requires acquiring a wiring diagram. You can do that here For the path to the schematic put in Interior and Driver Amenity for the system and Parking Aid for the sub system and you will get the O.E. schematic.

From service information, circuit/system description ;
Each object sensor is a 3-wire sensor that is both a transmitter and receiver that includes a signal circuit, a low reference circuit and an 8-volt supply voltage circuit. The object alarm module supplies 8 volts to the object sensors via the supply circuit and provides the ground. The object alarm module triggers the sensors in a sequential loop. After each sensor transmits the object alarm module uses the echo or signal return to calculate the distance and position of an object from the rear bumper.

Conditions for running the DTC
Ignition voltage between 9-16 volts
The vehicle is in REVERSE.

Conditions for setting the DTC
The object sensor signal circuit output is greater than 11.5 volts.


The owner has already replaced the sensor and that didn't fix the problem. He suspects that either the harness or the module has failed.

What would you test first and where would you perform the test?

Here is what the left rear outer sensor (in blue) and the left rear inner sensor (in red) signals looked like after the repair. The yellow trace at the bottom is the ground circuit voltage, and the green towards the top is the 8v supply.

stever

I'd get a spray can of electrical contact cleaner and spritz the module connections and jiggle it.

thecardoc3

If you were flat rate technician you would get paid .3 under warranty to diagnose this. The module is under the passengers side front seat and you would have to remove it and re-install it for access and that would be unpaid time.

BTW, for what it's worth that also would not have fixed the car and now you are working for free.

thecardoc3

There is a big difference between testing and guessing. Pulling a connector and doing anything without first making and recording measurements at the appropriate connections is guessing and bound to fail more often succeed. What's worse is when an attempt like that causes the problem to be corrected temporarily. You see posters complain all the time about failed diagnostic and repair attempts. This exercise is about how that is averted and the problem solved the first time.

I provided the information necessary to find the schematic. Make specific requests for testing data based on wire colors and pin ID's and I can provide the answer as if you made the measurement. Then attempt to analyze from that point and make your next test request.

roadburner

I'd just avoid owning a Chevrolet truck...

kyfdx

@thecardoc3 I am in actual need of some free advice. (see, it never ends, even here in the forums).

Purchased a high-mileage 2013 Audi A3 TDI, yesterday. All fine on the 100 mile drive home, but when I restarted the car, the MIL light came on. From my reading, it seems this is mostly emission equipment related.

The experts at AutoZone tried to pull codes for me, but can get no info, other than the VIN. Not even make/model. They think Audi has a proprietary system.

Do you think this is an Audi dealer only fix, or would my local independent who subscribes to all-data be able to diagnose it? Thanks!

thecardoc3

By MIL you are referring to the check engine light, correct? Anything that illuminates the check engine light should result in a code in the OBDII system. It is however possible that the communication data bus is down and the instrument cluster as well as their generic tool might not be able to communicate with all of the modules.

At this point its most likely a tool issue that has them not getting any (enough) information. A properly equipped indy should be able to help.

kyfdx

thecardoc3 said:

By MIL you are referring to the check engine light, correct? Anything that illuminates the check engine light should result in a code in the OBDII system. It is however possible that the communication data bus is down and the instrument cluster as well as their generic tool might not be able to communicate with all of the modules.

At this point its most likely a tool issue that has them not getting any (enough) information. A properly equipped indy should be able to help.

Exactly.. Audi calls it the Malfunction Indicator Light, but as near as I can tell, it's the same thing as a CEL.

Thanks!

thecardoc3

roadburner said:

I'd just avoid owning a Chevrolet truck...

As the park assist, lane assist, brake assist and other features are added to today's cars, more and more people are going to have to learn to deal with electronics at this level. GM isn't alone when it comes to experiencing failures with these systems and they darn sure aren't alone when it comes to poorly written diagnostic information.

I'm not surprised that no-one has made any attempts to work through this example. What I posted here hasn't even been shared on most technicians forums yet because it takes a lot of time to do the testing and collect the data on top of trying to be productive and still earn a living.

The failure this time is pretty simple and no parts were required to correct the problem. However isolating the failure for most isn't as easy as one might try to make it sound, especially when the trouble tree information, as well as the code description are very misleading. The code stated that the circuit was shorted to battery, the conditions for setting the code required the signal to exceed 11.5v, and the vehicle had to be in reverse. The code actually set the moment that the key was turned on.

Here is what the signals looked like when the circuit failed. The red trace is the LH inboard sensor at key on, and the blue trace is the ground circuit of the LH outboard sensor when the code set.



The rest of the time the signal circuit for the LH outer sensor looked like this.


The 8v displayed is coming from the controller, not the sensor. When you look at the initialization waveform the controller communicates to the sensor, giving it instructions and then it awaits a response. The response is created by the sensor pulling the 8v reference signal down and it never responds because of a faulty ground connection leaving the voltage high. As fast as the system detects a failure, it shuts down leaving both 8v signals (supply and signal) and the ground circuit intact. This is never explained in service information, nor is it explained how when everything works the module pulses the signal wire to ground, and then awaits the sensors response which provides both distance and signal strength in the coding.

Here are four more scope captures after the repair. The first one has an assistant moving behind the truck and you can see the changes in the response from the sensors after the module request. The next three are zoomed in captures of the data.






This is a very slow system with the request and reply occurring about seven times a second. The communication itself is taking place at about 5000hz. That is still way too fast for conventional testing routines.

stever

Bad ground eh? Guess I called it again.

You did jiggle it first, right?

thecardoc3

stever said:

Bad ground eh? Guess I called it again.
You did jiggle it first, right?

No you didn't (you guessed the module) and no I didn't jiggle anything first. (wiggling the wires before actually testing is a rookie mistake) The failure was the terminal inside the connector for the LH outer sensor. The scope connection started to bridge the failure which is why some of the initialization signal is visible on the ground.
If someone would have followed the trouble tree for the test of the ground circuit, which included pull the connector and front pin to the grey wire, and at the module connection they would have gotten a good connection and that test passed. Using the scope to test the circuit live showed the failure right away.

stever

You jiggle it to fix it, not test it. Amateur

The real question is why did you have to pull out an expensive tool and generate a bunch of read-outs when the dash should have just told you "module sensor failure"? (The next question is why this stuff relies on copper for the inter-module connections in the first place, especially in this kind of tough environment).

I know 2008 is ancient history but how many more years do we have to put up with this kind of junk?

thecardoc3

First, that expensive tool (the scope) is just one of the three that were pressed into service for this. To me, this was just another normal event in the shop. These tools were used on several cars that day and didn't just come out for one event.

The biggest concern with not testing correctly and completely is that when a circuit has started to fail due to age and conditions anything less than a complete proper repair will see it fail again. This time it was just a parking aid, next time it could be part of the autonomous driving system and it won't make an owner very happy if they have a random failure in some system like that if a shop can't fix it. Trying to just wiggle wires hoping to get lucky leads to making the problem hide instead of proving and fixing what was wrong the first time.

The whole point is that this IS what it takes to do the work and when faced with having to step up and approach the task correctly and efficiently no-one even tried and you only wanted to throw darts in the blind. Those represent the attitudes that have created the shortage of qualified technicians. The pressure to dumb it down only serves to make it less likely that you will find a tech who can handle this stuff someday when a customer (you) really need them. The routine that went into analyzing this sensor failure has to be practiced constantly or it doesn't get followed at all and that leads to inefficiency and failure to fix it the first time.

As far as how long do we have to put up with this stuff? Forever. These systems are just starting to fail on a regular basis. Most techs haven't had to do anything with them and almost no-one has spent time actually looking at the communication data with the scope as the different sensors identify and report obstructions as I did.

You asked why can't the dash just show "module sensor failure", because it just can't. The module cannot test past its connector. It can report if the voltage on a given circuit is too high, too low, open or shorted and in many cases use other inputs to determine if there is a performance issue with a given system but that is all they can do, and all they ever will do. It will still take a technician to prove why a module is not happy with a given input and solve the problem.

thecardoc3

Hey Steve. Here is what taking technicians talent out of the picture looks like.

http://forums.edmunds.com/discussion/41964/honda/cr-v/baulamistic-air-pressure#latest

stever

Yeah, some doofus comes along and figures out what the guy is talking about - oh yeah, that was me who (correctly) guessed that the poster was talking about a barometric related sensor. Seems like a case of GIGO more than a printer error on the diagnostic paperwork.

Mr_Shiftright

Steve's flying car of the future will be even more complicated than the ones we have now

thecardoc3

stever said:

oh yeah, that was me who (correctly) guessed that the poster was talking about a barometric related sensor. Seems like a case of GIGO more than a printer error on the diagnostic paperwork.

The diagnostic routine is as simple as it gets. The Baro sensor is inside the PCM instead of being separate components. So instead of addressing a wiring or sensor issue, the poster gets to deal with replacing the entire PCM. Instead of a $150-200 repair they are looking at $1000. IMO. You should be telling them how happy you are that Honda did this your way. After all it saved them $20 on the wages of the technician.

As far as guessing Baro, even a blind squirrel finds a nut once in a while. Accurately guessing the power ball numbers would be a notable feat.
(and like any guess non-repeatable)

Mr_Shiftright

Oh c'mon, give him SOME credit.

Actually I read somewhere that even squirrels with 20-20 vision forget about 75% of the locations where they bury their nuts.

stever

>The diagnostic routine is as simple as it gets.

Then why not have the car do it? And for $1,000 bucks, it should self heal.

(I hit the Power Ball two weeks ago - it's the other numbers on the tix that I keep missing).

Mr_Shiftright

Ahem...as Doc has pointed out, this would often require complex levels of redundancy. How does a module report back to you at ground zero when the elevator it uses is stuck on the 44th floor?

thecardoc3

stever said:

>The diagnostic routine is as simple as it gets.
Then why not have the car do it?

\

It did.

guitarzan

thecardoc3 said:

Het Steve. Here is what taking technicians talent out of the picture looks like.

http://forums.edmunds.com/discussion/41964/honda/cr-v/baulamistic-air-pressure#latest

LOL, recalling Rush Limbaugh's story from decades ago about his mechanic telling him that he replaced the "disgronificator". Does that part sound familiar doc?

Mr_Shiftright

The history of technology seems to tell us that when a certain system reaches an unbearable level of complexity, economic pressures will either create a new technology or a retreat to a simpler form.

I think we're there with automobiles.

Look at the commercial jets we fly

Look at the rocket motors we use to launch things into space.

Old tech---reliable.

Ever try to start up a steam car? Takes forever. Enter the 1912 Cadillac...turn the key, starter engages, and you're off.

Now I see there's a new thing called TwinCharging...combining a turbo and a supercharger. Gimme a break.

stever

thecardoc3 said:

stever said:

>The diagnostic routine is as simple as it gets.
Then why not have the car do it?

\

It did.

Right, so why not skip the tech and tell the driver?

thecardoc3

stever said:

Right, so why not skip the tech and tell the driver?

They did, by turning on the light and making a trouble code retrievable. And so that Honda owner is looking at a $1000 bill instead of one much more reasonable.

guitarzan

l

Mr_Shiftright said:

Ahem...as Doc has pointed out, this would often require complex levels of redundancy. How does a module report back to you at ground zero when the elevator it uses is stuck on the 44th floor?

Right, you cannot put in a test for a single connection. What is missing is easy access to these connections. If there were little labor in getting to them, then one could inspect/clean/replace all connectors in the offending system in a short period of time and tell the customer to come back if the problem returns.

Here is something I learned from the land of computers and programming: If reducing repair labor is not a spec given to the engineers, you definitely won't get it in the final product. If the mfrs. made this a priority, a great deal of repair labor would vaporize. Before someone retorts, "easier said than done", I can assure you, there are an infinite number of ways to design every system. The systems we get are merely reflective of individual decisions. Get it out of your head that, "They created the best design that they could." Nope. They gave the feature that was asked for. Everything else is gravy (or headache) generated by committee.

stever

>Right, you cannot put in a test for a single connection.

Why not? If you have an A/B switch and the circuit fails at the switch box, the error tracing should be able to tell that one or more pin-outs are bad.

Serious question - I've seen others throw this out there and it doesn't seem like a difficult problem to test for.

Mr_Shiftright

It's crazy to place a sensor near a hot exhaust manifold behind a power steering pump and that needs a special wrench to extract it, after you've broken the connector by merely twisting it.

guitarzan

Mr_Shiftright said:

The history of technology seems to tell us that when a certain system reaches an unbearable level of complexity, economic pressures will either create a new technology or a retreat to a simpler form.

I think we're there with automobiles.

Totally agree, in fact you were reading my mind. These fancy schmancy systems are a big cosmic joke, and I don't get the joke. But we must realize that, the consumer took us here! It's not like this stuff happens in a vacuum. People, society, demanded all of these features. What is wrong with people?

To me the car should have kept going down in price. I should get a brand new, $5,000 vehicle, that lasts 10 years. Instead the tenet of "it is better because it does more" has become a disease, taking car design in the opposite direction.

No doubt that safety is an illusion. People buy 5 star vehicles, with every added safety feature, then they all continue to tailgate each other down the 70 mph freeway. Guess what causes most of the accidents? The people think the latest bolt-on will save their life, when all they have to do is drive like a sane human being.

stever

Not to shift gears in mid-thread, but wanted to share this service review, since @thecardoc3 should appreciate it.

guitarzan

stever said:

>Right, you cannot put in a test for a single connection.

Why not? If you have an A/B switch and the circuit fails at the switch box, the error tracing should be able to tell that one or more pin-outs are bad.

Serious question - I've seen others throw this out there and it doesn't seem like a difficult problem to test for.

In a single wire you cannot programmatically report back that there is a short 1 foot down the wire, a melted terminal connector at the end, or the connected device/sensor is bad. It all appears the same from the connection. Unless like Mr. S. suggests, you double up the system. Of course, implementing higher quality wiring and connectors to prevent problems is more appropriate for the car than redundancy, which is far more expensive, as well as appropriate for airplanes.

thecardoc3

guitarzan said:

In a single wire you cannot programmatically report back that there is a short 1 foot down the wire, a melted terminal connector at the end, or the connected device/sensor is bad. It all appears the same from the connection. Unless like Mr. S. suggests, you double up the system. Of course, implementing higher quality wiring and connectors to prevent problems is more appropriate for the car than redundancy, which is far more expensive, as well as appropriate for airplanes.

Right on. I have said it over and over, the computer can't test the circuit beyond its connector. Then we have the Honda where the Baro sensor is in the computer, so it can in fact test the entire circuit if the engineers want it to do that. The result is a very expensive Baro sensor replacement compared to other systems that use a discrete sensor.

Oh, and doubling up the wiring only creates more chances for something to go wrong.

guitarzan

John Deere repairs anyone?

http://www.foxnews.com/tech/2016/07/25/farmers-fight-for-right-to-repair-their-own-tractors.html