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[WV Hillbilly]

I bought my 1997 Nissan truck about three years ago . The service engine soon light has been burning ever sinse I bought it . The truck seems to run great so I've never really been to concerned about the light being on . Now I'm wondering if my gas mileage may be suffering because of whatever's causing the light to stay on . The truck is a four cylinder , standard trans , & 4X4 . On a trip I get about 20-21 miles per gallon in 2 wheel drive . I have heard that autozone will read the codes & tell you what the problem is for free . I have also considered buying one of the less expensive code readers & checking it myself .
Your thoughts & suggestions would be greatly appreciated .

 

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[corklabus]

A free check from a parts store can't hurt anything. What good it might be would be considered questionable. FORD is the most original rip off company when it comes to identifying and correcting computer and sensor codes. They say "our equipment finds a bad one and it has to be corrected before we can detect another one." I say B.S.
My first impression in this case would first be to research the vehicle maintenance procedure. Many vehicles now require a special mechanical procedure to turn that light off when the regular maintenance is done "supposedly at the dealership by the dealership". If this is the case all you need to do is learn the trick to turning it off and then do it again when it comes back on every so many miles. Just another dealer rip-off trick.
If the free check from the parts store shows anything, it will be related to something a sensor is telling the computer. Often times the oxygen sensor in the exhaust is the culprit and reading the codes will say you have a rich or lean exhaust. This in itself usually isn't a problem because of the terrain we drive and weather conditions.
If the light comes on and flashes before you move the key to the start position, the system should all be operating properly and is probably the maintenance light aggravation mentioned earlier. After having the codes read at the parts store and making written note of what they are for later comparison, disconnect the positive battery terminal for 30 seconds. This will clear all the computer fault codes. Drive it for a few days and have it read again and compare any fault codes. If there are none your'e good to go. If there are some and they are the same, you have a point to begin looking for the problem. A fault code reading in the system will NOT tell you what is causing the problem. It only tells you which SYSTEM is causing the fault. Usually a sensor in the system is at fault and can be easily replaced.
BUT FIRST OF ALL....... Check ALL vacuumm lines for leaks and deterioration. Take them off wherever you can and shorten the ends if they even look bad.
SECOND.....check every visible section of wiring you possibly can. Look for wear spots that could create grounds or voltage leakage, bad connections or corrosion, missing insulation,etc;. You get the idea. 90% of problems can be tracked to aged vacuum hoses and wiring defects and can usually be fixed with little or no cost.
Since you only "suspect" something might not be right, I'd still just ignore the stupid light. I know dozens of people with the same stuck light. For gas mileage, put about 7 pounds more air in you tires than the recommended air pressure on the side of the tire. Drive the speed limit or less when you can and take your foot OFF the gas pedal every chance you get to coast down a hill. I gained 10 mpg just doing that and I ain't gettin' anymore Hundred dollar speedin' tickets either.

 

[SgtSki in MI]

BUT FIRST OF ALL....... Check ALL vacuumm lines for leaks and deterioration.

A little trick to check vacuum lines that I learned somewhere. Take a propane torch and open the valve (but DON'T light it!!!) Run the tip of the torch around your vaccum lines in question with the engine running at idle. When you hear the RPMs pick up, then you've found your leak! I'm sure this method is nothing new to a lot of people but I think it works pretty well.

-SgtSki

 

[corklabus]

Sounds like an interesting trick, but I'm not sure I would trust this idea. Any form of unexpected spark from anywhere could ignite the torch which could in turn ignite any stray gasoline fumes or leaks which could also cause battery fume explosions. I see this as a very risky way of hunting vacuum leaks and I'm not the brightest lightbulb in the lamp when it comes to doing risky short cuts.

 

[Mike Moutray]

It can't hurt to get the codes scanned for free at Autozone, but don't let them sell you anything on the spot. Autozone sells parts, they DO NOT diagnose. If you get the code scan, post what it is and the engine size of your truck and I'll try to lead you on the right path.... Take care, Mike.

 

[Starbuck]

Hillbilly,
I agree with what most of everybody else is saying a thorough visual check and then get the code or codes checked only. Your Nissan is an OBD2 vehicle. 1996 and newer light duty trucks and cars were built under new standards that require a standard set of codes that apply to all US vehicles. The code readers you mentioned are cheap but that is all they do is read and clear codes. If you need to see the actual sensor data (which in most cases is pretty important) you will have to spend a little more$$$ A good code reader that has all generic OBD2 data is the Auto X-ray it can be ordered through parts stores like Advance , O'Reilly's, NAPA and others shop around for the best price. If I were thinking about having my own scan tool this is the route I would go save a little more money and get the data capabilities too! For the time being get the vehicle scanned and lets see what code you have. OBD2 vehicles also monitor systems that were never tested on previous models for example the Evaporative system. This part of the vehicle prevents the venting of gasoline vapors to the atmosphere and stores them in a canister of activated charcoal until conditions are acceptable then the vapors are purged into the intake manifold and burned in the engine. A loose, incorrect, or poor sealing gas cap will now turn on a check engine light something we never tested during vehicle operation in pre 1996 cars. Get a free scan and report back to the forum and the folks here will probably be able to help.- Starbuck

 

[WV Hillbilly]

Thanks everyone . The service engine soon light comes on as soon as the switch is turned on &
doesn't blink or ever go off until the switch is turned off . I always wondered what the purpose of
the charcoal canister was . If I remember correctly the manual says the canister has a filter which
is supposed to be changed as part of the regular maintence . I've never changed it & doubt it's
ever been changed . I'll take care of that & get the codes read & check back in & let you know what
they tell me .