Please clear up my confusion. First you were talking about a gas odor by the left rear wheel. Now, for the first time you mentioned a burning smell while driving. A lot of things come to mind for a burning smell, but if we stick with the recent service, it is possible a wiring harness became mispositioned and is laying against something hot. That type of thing should be directed back to the shop that did the work so they have a chance to correct any mistakes they might have made. More on that later.
Not related to any recent service, some common causes of a burning smell are overheated and melted wires on the ignition switch, overheated wires or switch for the heater fan speeds, and a failing heater blower motor. Other wires can become overheated too in electrical connectors. All of those smells will subside shortly after turning off the offending circuit.
Even something as silly as the rubber strip along the back of the hood can allow normal engine smells into the fresh air intake if it is loose or mispositioned. Leaking heater cores will allow hot antifreeze to drip into a drain pan inside the car. That will cause an oily fogging on the windshield and a sweet smell, but some people describe it as a burning smell. There really isn't anything a mechanic could do to cause a leaking heater core. That occurs from the natural buildup of acids in the antifreeze over time. That acid eats away at metal parts and the heater core is usually the first thing to be affected. These acids are the reason we change antifreeze every two years.
If you do indeed have an electrical wire, connector, or switch contact overheating, the most common cause is from using the heater on the highest speeds a lot. The fan motor draws very high current which stresses the switch contacts and wiring. An overheated ignition switch is a very common cause of vehicle fires on Ford products. On other cars it mainly just makes an irritating smell and eventually some circuits will stop working. Most commonly the engine will stay running. The affected circuit is for the heater, radio, power windows, and possibly the dash gauges. If the heater fan switch is the culprit, the fan is the only thing that will stop working.
In general, if the smell stays the same whether you're moving down the road or standing still, it is probably coming from inside the car. If it gets more noticeable when standing still, it could be exhaust sneaking in from a leak in the system or it could be fumes from under the hood that normally blow under the car while it's moving.
There are a lot of reasons people, (not just women), don't trust mechanics, and most of them have valid explanations. There are disreputable mechanics just like there are disreputable tv repairmen, sales clerks, plumbers, etc. But it is unfair to hold an entire industry responsible for the actions of a few. Mechanics are actually held to much higher standards than doctors. When a doctor doesn't come up with the right diagnosis on the first try, we keep going back until he does. When a mechanic doesn't come up with the right answer the first time, we call him incompetent at the very least, or assume he is trying to rip us off. Doctors only have two models in varying sizes to learn. Only the cures keep improving. Mechanics in the 1960s could repair any system on any car in the world if they could memorize 5,000 pages of service manuals. Today they have to learn changes to hundreds of models with all kinds of variations to their systems sometimes twice per year. The insane addition of a computer to every part of a car makes things so complicated that it's almost impossible for anyone to keep up. Repair bills for these computers has driven repair costs through the roof and most manufacturers have their cars designed so you must go back to the dealer for these expensive repairs. Manufacturers profit handsomely from forcing you to buy their expensive replacement parts. Unfortunately, the mechanic is stuck in the middle being forced to sell you those expensive parts and services.
There is no longer such a thing as a mechanic who is an expert on even one brand of car. Young mechanics just starting their careers can do a little of everything, ... A little engine repair, a little suspension and alignment repair, a little electrical diagnosis, etc. But just as seasoned doctors specialize, so do mechanics. They are no longer a "Nissan specialist". Now they might be a "2004 - 2010 Nissan engine performance specialist" but know nothing about Nissan brakes or heater controls. For that reason, you might have a different mechanic work on your car at each visit to that shop.
I will never defend a disreputable mechanic or shop, but being a former mechanic and tv repairman, I've seen the best and worst of both worlds. Here are some of my observations that can lead to your mistrust. The person you spoke with at the shop was most likely not the mechanic who worked on your car. That is normal. Think of the mechanic as the doctor who pokes and prods you, and the service adviser as the person who schedules your next doctor's appointment. The doctor doesn't have time to do paperwork; he has to run to see his next waiting patient. Mechanics have very good diagnostic skills but they typically have rotten communication and customer skills. It's the service adviser who translates the mechanic's findings into terms you can understand, but most service advisers never were mechanics. A lot of them know little more about cars than you do so very technical things can get mixed up in translation. To add to the misery, two different mechanics will write their "story" on the repair order in different ways and two different service advisers will describe those findings in different ways. The two final versions might seem like they're describing two different cars but none of the people involved are lying or trying to mislead you.
Going back to your observation that the first mechanic said you had a bad catalytic converter and the second one said it was the mass air flow sensor, all that happened was the first guy stopped too soon. I can imagine hearing the second one say, "this car has a bad catalytic converter because it's glowing red, but let me check further. Hmm, there's no excessive back pressure so the converter is not damaged yet. I wonder what would be causing too much fuel to enter the engine". It that point, further testing would have also led the first mechanic to the sensor. He just jumped to the logical conclusion based on a quick observation and not enough diagnosis. Very often troubleshooting involves ruling out what is not causing the problem to narrow down the cause to what is causing it.
Some people will bounce from doctor to doctor looking for a diagnosis. To be sure nothing got overlooked, each new doctor will probably start from scratch and repeat what the previous ones did, so you can see how that is not the best way to approach the problem. Just like it's better to stick with one doctor you feel comfortable with, you will usually get better service when you stick with one repair shop that knows the history of your car. The service advisers at the very large dealership I used to work for knew most of their customers by name and their cars' service histories popped up automatically when the computer spit out the repair orders. While there are advantages with sticking with one shop, that becomes even more important when there's the possibility a new problem is related to their recent work. They should have the chance to correct their mistakes and apologize. That doesn't mean every new problem is their fault. Sometimes it's just coincidence that a number of things go wrong all at once.
Kind of related, most larger shops pay their mechanics on a system called "flat rate". That means every task can be looked up in a flat rate guide that lists the number of hours that job should take. He is paid his hourly wage for that job regardless of how long it actually takes him, and you will be charged for that many hours regardless of how long it takes or how many people work on your car. These guides let the shops provide you with a fairly accurate estimate that is in line with their competitors. It insures they will charge enough to cover their costs and they won't overcharge you.
As an example, I might pay my neighbor's kid ten bucks to mow my lawn. If he uses a scissors, it will take him all week! If he pushes a mower, it will take him all day. If he invests in a riding mower, it will take him an hour. Either way, it costs me ten bucks. The advantage of flat rate to the mechanic is if he invests in high-level training or expensive tools, or if he is very experienced and has done this same job many times before, he will get the job done faster. If he is being paid $10.00 per hour and does a one-hour job in half an hour, he still gets paid ten bucks for that job but he has extra time to get to the next job sooner. He is rewarded for sticking to business and working as quickly and efficiently as possible.
The checks and balances comes in when he makes a mistake due to his haste or he overlooks something. Under the flat rate system, he does not get paid again later to correct his mistake and you don't get charged again. That's another reason to stick with the same shop. Fortunately these mistakes don't happen often but when they do, that's what people remember and tell their friends about. They tend to forget all of the positive visits in the past.
A typical entry in a flat rate guide would look like:
Replace water pump
(4 cylinder): 3.4 hrs
(V-6 engine): 4.7 hrs
With air conditioning: add.6 hrs
That type of job is very specific and does not include the time it took to find it leaking or some other defect. The clock starts after the diagnosis has been done. Many shops do not charge for that diagnosis if it only takes a few minutes, but sometimes other related things get overlooked. For example, it is common for a worn water pump to ruin the drive belt. The cost of a new belt should be included in the repair estimate. Service advisers really hate it when the mechanic comes running up with a chewed up belt after the repair job is half done. Now they have to find you and tell you that more parts are needed than originally thought. The impression that leaves you with is "as long as you have your wallet out, I found something else to sell you". And if you agree to that part, they'll surely find something else later. You can see how that would make you mistrust them even though there was no intent to defraud you.
Sometimes the need for additional parts or services can't be foreseen until things are taken apart and inspected, but experienced service advisers will either warn you ahead of time or they might build those extra costs into the original estimate, then hope they can surprise you later with a bill that's lower than expected.
One last point. Now that I suggested you stick with one shop, if an estimate seems unusually high, there's nothing wrong with getting a second opinion. Doctors don't take offense at that and the only mechanics that would are those who are afraid they'll be found out for coming up with an incorrect diagnosis. The shop owner knows he might lose the job to a competitor but if that second diagnosis agrees with the first one, he knows there's a good chance you'll come back in the future.
Here's one thing to watch for with that second estimate, ... Well, actually both of them. There is nothing secretive about the flat rate guide. As long as the service adviser isn't busy with other customers, he should be willing to show you the labor times he is looking up. First of all, look at the book to be sure he is looking under "Nissan", not some other brand, and he is using the correct engine size and accessory information. GM cars are very involved and complicated. Their labor times will be much higher than for that same job on a Nissan so an unscrupulous service adviser might open the book to the GM section and show you that. Be aware too that there will often be two labor times listed. The shorter time is for vehicles still under warranty and are not practical. They assume no bolts are rusted tight or break off and the entire job goes smoothly. These times can rarely be met when you consider the time it takes to find the car, drive it in, get the parts, and test drive it after the repair. The mechanic does all of that for free. Usually there is only about a.2 hour difference between the standard and warranty labor times.
The last thing to look at is if there are multiple things being done to your car, do they each have separate labor times? As a steering, suspension, and alignment specialist, two jobs I did quite often were to replace the rack and pinion steering gear and replace the high pressure power steering hose on one particular model. Each job paid 3.4 hours so you would think I earned 6.8 hours pay for that car. In reality there was an entry in the flat rate guide that said the two jobs together only paid 3.7 hours. That's because all of the same things had to be taken apart to replace either part. According to my story for my students, that would be similar to paying for a five hour surgery for a lung transplant and another five hour surgery for a kidney transplant. If both were done at the same time, you might pay for six hours but not ten. Now, keep in mind that a brain transplant involves a whole different part of the body so while you might already be in the operating room, combining the two jobs might not always be practical when it comes to billing out labor times. Performing an alignment and replacing a muffler are two totally different things so there you COULD expect to be charged for both jobs.
For my water pump story, there will be an entry for replacing only the water pump belt, but that labor time is already included as part of replacing the water pump. It is not correct to add the belt replacement time to the bill. The belt, in that case, will be listed as included with the pump.
One final note, there are no labor times given for such things as smells, wind and water leaks, squeaks and rattles, or electrical problems. That's because there is no way of knowing what is causing the problem or how long it will take to diagnose it. Once the cause IS diagnosed, that's where the flat rate guide spells out how long it should take to replace something, but that will still potentially leave you with a separate diagnostic charge.
Hope I didn't bore you with too much information. Feel free to holler back with more questions.
Wednesday, November 10th, 2010 AT 11:55 PM