Mechanic shmechanic (semi-long read) (1 Viewer)

[Scott L]

I'm sure most here have a love/hate relationship with mechanics. Love when they fix the car, hate when you get the bill (harhar). Anyways, the Check Engine light in my car came on at 155k. I just knew my usual mechanic would charge me an arm and a leg for probably something relatively small so I did some searching on the net.

It turns out you can put your ECU into a diagnostic mode which will flash the check engine light in numerical pattens, giving you a 4-digit code (for my car anyway). So I did it and took this number to a site that's a big database for all 4th generation Maxima codes. Turns out it was a faulty knock sensor, a common problem with my year.

Some more searching led me to several DIY repair guides with pics included. They also said where I can get the sensor for $95, as opposed to $168.50 which is usually what the mechanic would charge. So I got the sensor but had reservations about installing it since I've never done any engine work or repair. I called my mechanic, told him how I got the code fromt the internet guides and all. He answered back in a condescending tone saying that you should never trust those and he'd have to run a full diagnostic test for $75.

I said thanks for your time and hung up. So let's see: $75 + $168.50 + $50 labor + tax!? No way, well not yet anyway. I ended up taking about an hour doing it myself. Got a still-painful manly gash on my right hand but it was worth $200.

So now the Check Engine light turned off by itself after about a day and my car accelerates much better below 3k RPM. Next up; replacing brakes!

 

[Kevin_Spradley]

I know what you mean about the mechanics responding in a condescending tone. My check engine light came on in my Durango, so I checked the code myself using the on-board diagnostics and also an OBDII reader. I notified the mechanic and they replied "we have our own set of codes, you need to bring it in and let us check it for $75." I took the car in for them to check it and perform the work. When I picked up the car and the receipt, the engine code listed on the work order was the same f****** code I had determined. I have not been back to that mechanic.

 

[LDfan]

You can also go to any Autozone store. They will hook up a scanner and give you the codes.
My 99 Accord has had the check engine light on for over a year. Runs fine despite the fact the computer is saying I have a bad EGR valve. I replaced the EGR valve and the computer is still pissed.

Jeff

 

[Al.Anderson]

Jeff, from what I understand, on many cars you have to manually reset the light after the problem that caused the light is rectified.

 

[Jay H]

Some cars you can use the dashboard trick to read the OBD code. I believe any OBDII car, like 1997 and later the dashboard trick doesn't work anymore and you need the OBDII scanner.

Not sure if car-wide, but my '97 BMW had to use the scanner to read the code.

Yes, there are certain car-specific codes too but no point not trying a cheaper generic scanner first before shelling $$ out to the dealer...

Jay

 

[Zen Butler]

A mechanic never wants to finish the job of another. Or in this case the diagnosis of someone else. People seem to think a mechanics diagnosis time is free.

1. Many times, if you get the work done there they will factor in the diagnostic hour into the labor time on the work order.

2. It's only tax on the part, not the labor.

3. $168 is what a knock sensor for a Nissan Maxima costs from the dealer.

4. 1.5 labor is what you charge for remove/replacement of a knock sensor(91-95ish Maxima) $75 + $50 = $125(1.6 labor @ $75/hr labor rate). Looks as if he factored in diagnosis into the total time.

5. If you wanted a cheap aftermarket part you should have told your mechanic about your budget.

6. To get a guarantee from your mechanic, he should diagnos the problem. Find a backyard parts slapper if you just want to swap parts in hope that it fixes your problem. Of course, with no guarantees.

7. Your mechanic's quote was on the money.


Just a different angle.

 

[Scott L]

Now whoever said the replacement was a 3rd-rate no-name backyard POS part? It was new Nissan OEM which is cheaper either through eBay with a seller of 99.5% feedback or any online parts dealer.

I know they have a thousand dollar diagnostic machine but for the possibility it is something small (which it was), that's an awful lot of money to spend outright.

I appreciate the different angle, I guess I'm thinking it was the mechanic's fear and maybe his ignorance of how useful the internet can actually be to stomp it out that it could be of any use at all for the average Joe to fix their car. Much like how dealers hate people looking up the real invoice value of new cars on Edmunds.com. It's a common problem with my car and thousands of people before me did this. Guess I just got lucky this one time.

 

[Steve Schaffer]

We don't do work based on another person's or shop's diagnosis without informing the customer that there is no guarantee.

In other words, if a customer comes in with his own part and wants us to put it in, we will do so with the provision that we do not guarantee it will fix the problem.

A bad Knock sensor code can just as easily be caused by an open circuit in the wiring as by an actual bad sensor, especially at 155k miles.

We also tend to want to check codes for ourselves rather than trust that the customer has the right code, but this only takes a few minutes. Sometimes another shop will have written down the wrong code number or the customer may just have been told the code number verbally and may not have a perfect memory.

All that being said, I congratulate you on solving your own problem and replacing the part yourself--feels really good doesn't it?, and not solely because of the money you saved. Wear that manly gash proudly!

Good luck with the brakes, they usually aren't nearly as bad as knock sensors, injury wise.

BTW, most obd II systems will cancel codes if you interrupt power for the ECM's memory circuit--look for fuses marked "EFI" and remove them for a minute or so, or just disconnect the batter for a minute or so. Some codes will not reset right away if the problem is still there, many require the malfunction to occur twice with a key-off cycle between occurences.

For the guy who replaced the EGR valve to no avail, these are usually operated by vacuum and are switched on and off by electric solenoids--EGR is usually turned off when the engine's cold and always turned off at idle. A bad vacuum switching valve, clogged vacuum modulator, clogged egr passages in the intake tract, or just a vacuum hose adrift can disable the EGR system and cause it to throw a code.

In my experience failure of the egr valve itself is extremely rare. You can check if it's working by warming up the engine and lettin it idle. Disconnect the single vacuum hose going to the egr valve itself and apply vacuum directly to the valve--the engine should start to sputter or even die. If it doesn't then the valve itself is bad or more likely the egr passage is coked up.

 

[Philip_G]

sounds like an ODBI car, both of my current cars are ODBI, but I have a PC based ODB scanner from previous cars, sometimes it's right on, sometimes it's a hint at a symptom of a problem. Personally with the advent of the internet and the availability of information and advice I don't use mechanics for anything. Sure, I'll probably pay someone to put a clutch in my miata, only because it's so low to the ground that it's not worth my time without a lift.

Now, anyone want to help me diagnose a multi-temp sensor problem with my audi?

 

[Dennis Nicholls]

The regular scanners will also read the mfg. specific codes. You just need to find a table of these codes someplace online. E.g. for Ford http://www.svtlightnings.com/scantoo...tc%20codes.htm .