Water Cooler Diagnostics
We’ve all heard the phrase, “codes don’t fix cars, good diagnostics does”. Codes are merely a direction or path, not the answer as some might think. Those “codes fix it all” believers are usually at the bottom of the diagnostic chain. You know the type; those Neanderthals with little wrenches and big cheater bars, or the ones that follow the old adage, “When in doubt-rip it out” method of diagnosing a problem.
It’s seems to me that car repair for a certain demographic of people has always been something related to hand-me-down repair information, not diagnostic skills. I believe it’s all because of the availability of cheaply made parts and bad information. Some of it is hearsay, but a lot of it comes from two guys chatting next to the water cooler at work, and neither one of them have any automotive diagnostics background at all.
This latest case study is a perfect example of why swapping parts and paying attention to those water cooler experts isn’t always a good idea. A trained technician with diagnostic background and less time at the water cooler may be what you need.
A 2007 Dodge 4.7L pickup came into the shop with a stalling problem. The owner had already stopped by the water cooler and made a trip to the code fairy. Since no codes were stored, there wasn’t much for him to do except follow the water cooler genius’ advice. He swapped out every sensor and computer part he was told about and a few more he could barely reach, just to be safe. All of which didn’t change a thing. Before writing up the work order, I had to listen to his story, which ended like most of them do, "I've already spent too much on this truck, and I don't want to spend a penny more." (I wonder what kind of commission the water cooler guy got from the part store for helping this guy spend all his cash.)
The stalling was pretty predictable, usually every 15 minutes. Just as it would stall, the check engine light would rapidly flash, then the truck would sit silent. If you turned the key off and back on, the truck would run perfectly as if nothing happened, right up to the very moment the whole scenario repeated itself.
Since the only odd thing was this momentary flashing of the MIL, I decided to hook up a scanner and wait to see if this odd failure would show up on the screen. Sure enough, code P0688 popped up momentarily, just as the truck stalled “ASD signal low”. Out of habit I reached up and cycled the key. Dang it, the code never stored and the truck is back to running correctly again. I’ll have to wait one more time and see if I actually had the right code number. Since it only occurred as it went through its death roll, catching this failure was going to be tricky.
It was the correct code alright, but no signs of dropped voltage or weak connections anywhere to be found. It’s time to pull out the big guns. Break out the scope boys! With the scope hooked up to two different injector leads and the remaining channels on a couple of coils, I spent the afternoon watching the ASD voltage like a nervous hen watching her chicks. As if on cue, the truck died. Not a bit of change on the scope. I’m definitely going at this the wrong way.
Something is dropping off, or at least I assumed it was. Instead of looking at the ASD signal, how about checking the injection signal and coil signals from the PCM? This time the scope did have a weird response. Just as it stalled there was a little extra squiggly line that didn’t belong in the pattern on the coil input leads. Very subtle difference, but enough of a difference that it needed closer attention. The voltage signal spiked a bit higher than normal just as the truck would stall, and then the voltage would drop to zero. It must be the PCM or a coil. Since the signal was only there for a brief blip on the scope, it wasn’t exactly something I could put my finger on just yet.
Time for some old school tricks. Since the PCM was new, I could at least (with some trepidation) rule it out for now. I could test further, or I could try to create a problem that might mimic what I was seeing on the scope pattern, or with luck, if it was a spike that was coming from a coil, disconnecting it could show the problem. I decided to give this truck a miss of my very own and see if I could increase that little squiggle into a bigger one.
I'll unplug one coil and watch the scope pattern. If I’m lucky, the truck will either stay running longer than it normally did, or it might show me a larger voltage spike. Sure enough, I found it on the third coil. As long as that particular coil was left unplugged, the truck ran well past the usual stall time. To verify it, I plugged the coil back in and watched the scope readings directly at that coil. A millisecond before the stall the coil spiked to the top of the screen as the truck shut off. Just as I suspected, if it was on the coil that was causing the problem the spiked voltage would show higher there than on the adjacent coils.
The big question for me was why did it not set a code? The reason was the coil lead led straight to the PCM. The extra high voltage going back into the circuit simply turned the PCM off as if the key was turned off. There’s no codes for shutting the truck off, only codes for failures that make it shut off. The solution...replace the coil.
Now and then there are problems that don’t follow the diagnostic steps laid out by the engineers. Even though you’d think every aspect and every type of condition has been tried and tested, or at least talked about around the water cooler. There are times when you’ve got to look past the “assumed” problem and dig a little deeper to find the cause. There's no doubt this repair is going to be another one of those conversations around the water cooler, but I seriously doubt anywhere in this story will the novice know-it-all admit that it took an experienced technician to locate his problem, not his water cooler buddy. Oh, and I don’t expect to hear him say as he leans on the cooler, “Codes don’t fix cars, mechanics do” even when there isn't a code.
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Thinking Outside the Box
An 04‘ Ford pickup came into the shop with a non-functioning cruise control system that had already spent some time at a couple of other shops. None seemed to give the customer any kind of answer as to why the cruise control wasn’t working. And, like many of these types of jobs I get in from those “other” shops, they all eventually come to the same conclusion as to what’s wrong with the vehicle. You know, the typical bail out answer for a problem they couldn’t solve. They’ll tell the customer, “It must be electrical”, and of course, they don’t do electrical. Seriously, what isn’t electrical these days?
A lot of times I find the term “It must be electrical” is just an excuse from these other shops to throw their hands up and send the customer down the street. They either don’t understand the diagnostic procedures or have already spent way too much time swapping parts and components hoping they’ll eventually run across a solution rather than actually diagnosing the symptoms.
I’m not one to shy away from some “electrical” problem. I’m more than a bit bull headed and stubborn enough to stick it out to the very end. Even if that means going to the extreme to diagnose a given problem. This one was no different. But, first things first, as always, verify the customer’s complaint. So, off on a test drive I go. Sure enough the cruise wouldn’t engage. There was no green indicator on the dash and no signs of any action taken by the PCM to engage the cruise. Now, it’s back to the shop and grab the scanner.
Codes were absolutely no help. No codes were stored and no history to see. Which, is probably where these other shops stop testing things and came up with their conclusion, “It must be electrical”. For me, codes are only step one of many to solve an electrically related problem. Let’s face it, codes are not the defining answer. Today’s cars have so many different methods of watching the various components involved with each system that it just makes sense to use the scanner as a tool to aide in diagnosing, and not just simply for reading codes. For this problem using the scanner to look at the PID’s (Parameter Identifications) was going to be more than a bit helpful.
As I’m sitting in the service bay watching every function involved with the cruise (according to the operation description), I did not see anything out of place or giving me incorrect readings. Everything from the emergency brake signal to the BOO (Brake On-Off) signal were correct. There didn’t seem to be anything standing out as the culprit, but there had to be something, something that everyone else has overlooked. Sitting in the service bay is not where the cruise control does its job. The vehicle has to be brought up to speed, before you can rule out if all the various components are actually working according to the manufacturer’s specifications. So, it’s back out on the road, but this time with the scanner installed. The safest method is to have a co-pilot watching the laptop screen. With the truck moving down the road there was only one item that didn’t act the same way it did when the car was stationary, and that’s the BOO signal. As we drove around the BOO stayed ON all the time. It never switched from ON to OFF when the brakes were applied.
It’s back to the shop to try this whole thing again. This time I left the engine running and watched the BOO signal. As I pushed the brake pedal down, the signal switched back and forth from OFF to ON just as it should. Now what in the world is going on? I know I saw a constant ON signal while we were driving, but it shows ON/OFF as we are sitting still. That’s when I reached over and dropped it into drive and allowed the truck to roll forward just a bit. Well what do ya know, the signal never switched anymore. But, in park it worked just fine. I tried the same thing over and over again, and every time I had the same results. It can’t be the brake switch, I’m not changing anything there. The only thing that’s changed is the gear selector. So it’s got to be something with that. Could it be the TR switch? (Transmission Range) Nope, it’s working perfectly. So, what else can it be?
I went back to the description and operation page of the service manual, but even after reading it a second time nothing seem to make sense as far as what I was seeing on the scanner. But, there was one thing I thought might be involved that the general description page didn’t mention anything about, and that’s the shift interlock switch. According to the wiring diagram there is a signal for BOO at the shift interlock, but only briefly mentioned as a possible cause of loss of BOO signal in one of the sub headings regarding the diagnostic procedures for testing the brake switch. Still confused, but willing to go with the “It must be electrical” as the primary cause of the problem, I decided to check further into the shift interlock switch. This time instead of driving it or spinning the roulette wheel of possible components, I’m going to pull the shift interlock and check it myself.
From the outside of the little box everything looked great, all the connection are solid and there were no signs of something that might have been spilled into the console. The circuit box was not glued together and could easily be taken apart, and I had a pretty good idea it had to have something to do with the BOO signal going awry, it seemed like the logical thing to do. After I opened up the box, all I could say was, “Holy cruise controls there’s the problem!” A transistor had a burnt terminal. Now I’m more than confident this is the problem, time to order one.
After installing the new shift interlock I took it down the road for a quick test drive. The green cruise indicator light came on, it accelerated, resumed and functioned just as it should. The shift interlock was definitely the problem. Of course, just to prove my hypothesis that it was the cause of the entire problem, I had to perform the same test I did earlier by placing it in and out of park and letting the truck roll forward while watching the laptop. The BOO signal was doing its thing. ON then OFF just as you’d expect it to do.
It’s not the first time I’ve run across a diagnostic situation where all the PID’s or information given wasn’t in plain English. Sometimes what you have to do is go that extra step and follow your instincts as to what you believe is the problem. I’m sure another sharp tech would have a completely different way of coming up with the same answer, but in this case, this is how I came up with it, and it worked. That’s what counts in the end. The customer is happy, I’m elated and you can be sure I’ll be watching out for the same kind of problems in the future, too.
Even though my diagnostics information didn’t have all the answers laid out with pinpoint accurate details the answers were still there. Ya just had to dig them out from between the pages of the diagnostic manual. As with a lot of today’s electronic mazes, you might find yourself having to solve a problem that wasn’t a problem just a few years earlier. I mean seriously, who would have thought a shift interlock would have something to do with the cruise control 20 years ago? Or for that matter that you could look at so many different sensors or components all at the same time on one tool.
At times it does seem like an uphill battle to keep up with all the changes in the modern mechanics field, but at the same time very gratifying when you overcome a problem that seemed impossible to solve. Sometimes, ya just gotta think outside the box or in this case… open it up and look inside.
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My new policy is if a customer says he just came from another shop I want to know what shop, how long it was there for and what it was there for. Then I will give that shop a call and see if the story checks out.
Dealing with a situation with a RIDICULOUS customer that I come to find out was pushed out by 2 other shops.
By Joe Marconi
My manager took day off yesterday, so I decided to step into his role and oversee shop production for the day. Boy, the things I uncovered! How does anything ever get done? The schedule is a mess, jobs not checked out early enough, too many wait customers, too much conversation among the techs, and they even took a lunch break!
By noon, I was so frustrated that I needed a gin-n-tonic to calm down. (Just kidding, actually drank an Ice tea).
I pushed all morning long MY WAY, and everyone pushed back. So, after their “Lunch break”, I decided to do more observing than interfering. And guess what happened? By the end of the day, all the work was done, all the customer problems were solved and everyone ended up on a high not. What? How could this be?
I need to take some of my own advice, and let go of control. Not doing things MY WAY is not always a bad thing.