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The Check Engine light (or Service Engine Soon, etc.) has a reputation of being the most cryptic, alarming, and sometimes trivial dashboard warning light.  Cryptic because it could point to any problem and you need a mechanic's computer to diagnose it; it gives him a code which he then interprets.  It's often not as catastrophic as it sounds and probably points to a simple emissions problem.  Don't assume you have to stop right away and get towed.

Anecdotes aren't worth much, but just as one example, my mechanic once left my throttle cable in a stretched position after servicing my car, which had me revving too high and was enough to turn the light on.

But depending on the car, if the light is blinking, it might point to an engine misfire.  Or so says my Nissan manual.
 

Recent studies have shown that 95% of all check engine light occurrences usually follow a messy and tragic explosion. Last year Ford Motors proudly announced having the safest post check engine light vehicles, boasting a family incineration rate of only 40% or so. Automotive calculates this means that Ford vehicles only melted around 30,000 Ford riders and drivers into the chassis of their vehicles in the last year. Personally I'd suggest doing what can be considered as the only safe/smart move in a check engine light scenario: Douse the car in gasoline and set fire to it. Kill your car before it kills you.
 

I have a drivetrain service light coming on in my jeep grand cherokee.
Any ideas what might be cousing this and more importantly how do i fix it?

thanks
 

the electrical system on my car has a short of some kind where the check engine light periodically comes on for short stints. i've taken it to the different mechanics and they can't seem to find out exactly what the problem is, the car is in decent driving condition with no glaring engine problems. they simply reset the system and it goes away. i've heard that the lights on a dash are like a street signal. if its yellow you need to slow down and get it checked out as soon as you can. whereas a red light means stop and get immediate help.

hib96 wrote:

I have a drivetrain service light coming on in my jeep grand cherokee. Any ideas what might be cousing this and more importantly how do i fix it? thanks

Yeah, even a loose gas cap will cause a check engine light to stay on. It costs around $50 for my mechanic to reset the light.;(  

My engine light came on as an A2 sensor warning... Not sure what the O2 sensor does... Senses O2 i suspect... Anyway, they reset it for 75$.   1 week later it came on again...  Can I reset it myself?   they said 200$ for a new sensor.  That is steep... Do I really need my O2 sensed that badly?
 

BigJaws wrote:

My engine light came on as an A2 sensor warning... Not sure what the O2 sensor does... Senses O2 i suspect... Anyway, they reset it for 75$. 1 week later it came on again... Can I reset it myself? they said 200$ for a new sensor. That is steep... Do I really need my O2 sensed that badly?

(1991 Ford E150 van V8 302)
Any help would be appreciated.  The van is undependable.

Right after I replaced a leaking float in my forward gas tank, the check engine light started coming on and the engine began intermittently balking (quickly cuts out then in) off and on.  Thinking there was cause and effect, I replaced the whole fuel pump assembly for the tank, including the vapor control valve and grommet and the lock ring rubber gasket.  However, the check engine light still came on and the balking continued.  

So, after reading the possible causes in my Haynes manual, I replaced the distributor cap, rotor, pcv valve, air filter, oil filler/air intake filter, and the in-line fuel filter (underneath the van attached to the frame).  I removed plugs 8 through 3 and checked the plug and gap which are OK.  Plugs 2 and 1 are very hard to get out, so I skipped those for now.  I added a thin film of dielectric silicon grease to the plug wire and spark plug connector for corrosion resistance and ease of removal.  

Now it takes much longer for the check engine light to come on (4-10 miles) and it now goes back out, on and off.  The balking is still there, and appears to be OUT of synch with the check engine light, but it takes a lot longer for the balking to start.  I have the engine cover off and there is a distinct loud clicking sound when the engine balks.  I can’t tell where it is coming from or whether it is a cause or an effect.

The next steps (not in order) I can think of are: (0) call Car Talk when they get back from vacation, (1) replace the in-fuel-line canister attached to the van’s frame forward of the forward gas tank, (2) replace the plug wires, (3) replace the gas tank caps, (4) replace the in-line fuel pump forward of the forward gas tank, (5) replace the coil, and/or EEC microprocessor and/or ignition module (6) start replacing other emission control components, (7) take it to a garage that can plug into and read the diagnostic system, (8) take it to a dealer.

Allen wrote:

(1991 Ford E150 van V8 302)
Any help would be appreciated. The van is undependable.