Automotive problem analysis

Factual Questions
1

I drive a 1996 Nissan 200SX SE-R (it has been a fine car – essentially trouble-free). It just turned 90k miles, and the “Check Engine” light is now on. I guessed it might be asking for a new oxygen sensor (or similar) so I stopped by the local Nissan dealer.

Once, at about 30k miles I had a Check Engine light during a trip. I stopped at a dealer and in about 3 minutes a service guy had connected a hand-held analysis computer to my car and then to a printer, which produced a page of information on my problem (a stuck PCV valve, easily fixed).

But now my local dealer wants me to make an appointment. I was told that it takes “45 minutes to an hour” to “pull a code.” They basically denied that my previous experience was relevant.

Does this make sense? Is it typical? It seems that they are saying that it takes as long to diagnose a problem reported by the engine computer as it did when there was no such computer.

I recall being told that some car models can be made to “blink” the problem code so that it can be read without the special computer. Is this common?

2

On some vehicles, the check engine light comes on automatically at exactly 60,000 miles. I just had this happen on my Mazda, checked the manual, and sure enough. It doesn’t necessarily mean that anything at all is wrong, but rather that the manufacturer wants you to have the emissions systems checked. Seeing as you have a Nissan, your mileage may vary.

3

Hope this helps. From 10.11 Nissan Electronics Diagnosis:

Following that are some explanations of the codes.

4

You can also go to any nearby Autozone. They should be able to check the code for you for free. Or, if you think you are going to be doing a lot of this, you can by an OBD II scanner for yourself. They are probably around $50.

5

Xema, Yeah it probably only takes 5 minutes or so to shag your car from the lot, find the scan tool, hook it up read the code, and write it down. But I’m going to go out on a limb here, I assume that you would, at that point want the car fixed. Cars don’t fix themselves (and it takes time). By allowing one hour or so in the schedule, they will have time to read out the code, determine the source of the problem, and then fix your car. They will also have time to fix the others that they have scheduled for that day. (Some cars may take 2 hours to fix the next two may take 30 minutes each) If they said sure XEMA bring your car down we have 5 minutes to spare. You would show up, they would read the code and then tell you to come back another time, as there is not time in the schedule to do the repair. Not a good way to satisfy customers.
Why do they use appointments? Simple, to prevent 300 people from showing up on Monday and 6 on Tuesday. Shop scheduling can be a bitch, shops take appointments for the same reason your doctor does.
On the cars that I teach on there is something like 130 different engine management codes which after all the different combos (signal high, signal low, short to power, short to ground) makes up something like 450 different codes. And that is just for the engine. So yes it does take some time to read the codes and then figure out what is wrong. Oh and just because a code is listed for item X has a bad signal that does not always mean that X is bad. The wiring to X could be bad, or another sensor could be out of range making X give a wrong reading.
Ringo I don’t have a cite, but I am fairly sure that by 96 Nissan had deleted the flashy lights from their control units as a 96 is probably an OBDII car. Squink Those were actually a service reminder light, not a malfunction indicator light. They came on every 30 or 60,000 miles to remind the owner to tune the car up. Last one I saw was in the early to mid eighties. Cars with real check engine lights don’t use a 30K/60K reminder light (although they may have oil change reminder lights)

6

I second what Rick said, except–some manufacturers do indeed use the “check engine” light as a maintenance reminder, in addition to its warning function for the electronic control system.

As to this: It seems that they are saying that it takes as long to diagnose a problem reported by the engine computer as it did when there was no such computer.–Yes, and sometimes it takes longer. There seems to be a common misconception that the ECU (“computer”) tells right away what needs to be done. While occasionally this can be the case, it’s not at all unusual to find that the information provided is only the starting point. Sometimes it takes a fair amount of testing and evaluation to pinpoint the cause of the problem. These systems are complex, and not all of the problems they pose are as simple as a stuck PCV valve.

I don’t see anything unreasonable in the dealer’s approach.

7

Thanks for the help. I finally managed to Google my way to some detailed instructions (similar to what Ringo found) for reading the code without a special computer, so I’ll try that when I get time (car continues to run fine through all this).

The service manager who spoke to me made it fairly clear that the 45 minutes to an hour was only to “pull the code” – repair time would be extra.

Much of my less-than-thrilled reaction to this was based on my previous experience where, instead of taking a couple of minutes to explain to me how long it took and that an appointment was needed, the guy just whipped out the computer and read the code. Basically zero time was needed to interpret the code – he simple connected the diagnostic computer to a printer, and the whole story was neatly printed out.

I remember telling muself that Nissan was really up to speed and using computer diagnostics to help both the customer and their service departments. Now I’m not so sure.

8

Uh, Xema, are you female? I’m asking because some car mechanics think that they can scam a woman, so they might be planning on pulling a fast one on you if you are. Which would tell me that I needed to find some place else to take my car. If you go to Car Talk’s website they have recommended garages from listeners, you could check to see if there’s one in your area.

9

*The service manager who spoke to me made it fairly clear that the 45 minutes to an hour was only to “pull the code” – repair time would be extra.

Much of my less-than-thrilled reaction to this was based on my previous experience where, instead of taking a couple of minutes to explain to me how long it took and that an appointment was needed, the guy just whipped out the computer and read the code. Basically zero time was needed to interpret the code – he simple connected the diagnostic computer to a printer, and the whole story was neatly printed out.*

I’m going to make some guesses here as to the discrepancy between these two experiences. I’m in the auto repair field, which gives a fair bit of knowledge in this area, and I’m sure colors my perspective on it.

It’s true that hooking up and reading the trouble code memory can be done in a number of minutes. But most shops–especially the good ones–are busy, and cannot make themselves available for drop-in, do-it-right-away, while-you-wait service. Their days are scheduled, and they work on an appointment basis. And because auto repair doesn’t always proceed exactly as planned, it’s not possible to predict to the minute when they will start–or stop–on a given car. Some shops would insist you leave the car for the whole day, not because of how long they expect to be working on your car, but because of the logistics involved in taking care of multiple customers with various needs. A window of an hour to pull the codes strikes me as more than reasonable.

Another possible factor may be the psychological aspect of what they charge for this service compared to the actual time consumed doing it. The fee for code-reading may be the better part of their “hourly” charge. Auto repair is not billed by the hour (60 minutes on the clock), but by the job (often by the “flat-rate hour,” which is NOT a unit of time). The professional scan tools used to interact with the computer cost thousands of dollars, and properly run businesses are going to factor that into the price for using them. So if they charge, say 50 bucks to read the codes, and it takes them 5 minutes, they may want the car for an hour to avoid folks’ getting the feeling that they’re being overcharged.

In your previous experience, apparently you lucked into a situation where the shop was not terribly busy. They may also have given you some priority because you were traveling, where it would be very difficult for you to leave the car or wait for an appointment. And it was a different business in a different place; they just might do things differently.

So in answer to your questions in the OP–Does it make sense? Is it typical?–I would say yes and yes.