In a move to the states (Hawai’i), I will most likely be obliged to purchase a second hand car. Was looking at ads on Craigslist and sometimes you see an ad (for a car) and in the ad, occasionally you will see written as part of the description: “check engine light is on”.
Does this mean that the car is going through its death throes? Should be avoided at all costs? What does such a general warning mean? When I was young we used to call these sort of warning signals “idiot lights”.
(Most likely I will be starting an opinionated thread in the correct forum area as to which make of vehicle folks recommend for reliability and gas mileage)
In my car, it could mean anything from gas vapor pressure in the emissions system to a misfiring cylinder. If you live in an area where an emissions check is required, it could make the car fail. In fact, you couldn’t even get the car checked with a lit engine light. No emissions check, no registration. You should have a mechanic check the code to see what the computer says the problem is, and if it’s going to be an expensive repair, I’d walk away from the sale.
On my car, though, sometimes it means I just have to unscrew my gas cap to release vapor pressure, then replace it, start the car, and drive it until it’s warm three times.
If the light is on, walk away. It means there’s something wrong with one of the systems in the car. It could be anything from, as Grrr said, a loose gas cap, low tire pressure, to a very expensive system failure. Bottom line, NEVER buy a used car without having a mechanic check the car out and list what is wrong with it. Never buy a car with a check engine light on unless you have an estimate to fix it in hand, an estimate YOU got, not one furnished by the owner.
Yeah, while it technically *could *mean anything, the context makes it unlikely that it’s something like a loose gas cap or a catastrophic engine problem.
A check engine light mentioned in an ad for a car that is otherwise presented as being all tuned up and running fine probably means it can’t pass a smog check and may need a new catalytic converter or something to pass inspection.
What it literally means is that someone with the correct equipment needs to check the fault codes that the car’s computer has stored, and then fix the fault.
I tend to avoid cars that have the check engine light on. The code tells you what the engine computer thinks is wrong, not what is actually wrong. Often, the computer is right, but sometimes it’s not. For example, what you think might be a simple gas cap code could actually mean the purge valve is shot, which is a more costly repair.
I always assume that if the check engine light is on, the owner already tried to have it fixed (since most folks don’t want a car that won’t pass emissions) and failed to fix it for a reasonable price.
It’s not optimal, but it’s certainly not a show stopper, especially if the price is right. As mentioned when buying a used car it’s wise to have a reputable shop put it on the lift and inspect it, check the codes and generally give it the once over. They have the experience and training to look for things that are often missed, like previous collision damage and repaint, or flood damage amomg other things. Often just the casual mention of having the car professionally inspected will cause unscrupulous sellers to start acting sketchy and maybe get pissy. Anyway a “check engine” light isn’t necessarily impending doom, but somebody needs to pull the codes and see what’s what. Incidentally an inspection like this should probably be less than $100, well worth it if a car seems otherwise a good prospect.
I highly recommend getting a bluetooth diagnostic scanner, which plugs into your car’s OBD port and transmits all kinds of information to your smartphone, including all check engine light codes. You can even use it to turn off the check engine light.
By law, the “check engine” light is supposed to come on when the PCM senses a condition which can cause the vehicle’s emissions to exceed its certified levels. It’s also supposed to store diagnostic trouble codes (DTCs) to indicate the condition(s) it detected which caused it to activate the CEL. And the list of possible DTCs is long.
A flashing check engine light means the PCM is detecting repeated misfiring and means you should stop the car else risk destroying the catalytic converter.
It can be a show stopper if your state has mandatory emissions inspection, because your car automatically fails if the CEL is on.
In my view - the presence of a warning light should be a deal breaker, unless you are a mechanic and have access to the correct diagnostic equipment with the expertise to interpret the results.
It’s not unknown for sellers to clear the codes to get the light out, which, if they haven’t cured the underlying fault, is only a temporary cure. In the UK, legislation gives us some protection if the seller is a dealer, but it’s hard to enforce with a private seller. Cars are so complicated now that ‘shade tree mechanics’ can’t cut it anymore.
jz78817 has it exactly right. It’s just the car’s computer telling you that something that affects the vehicle’s emissions is (or has been) not working perfectly. You can but a code reader at most auto parts stores for about $20. Doesn’t have to be bluetooth and fancy. The problem could be anything from a $10 rubber gasket on the fuel cap, to thousands of dollars for a new catalytic converter on some cars.
The CEL is not a deal killer, but it’s a negotiation point.
The answer to the OP is “Some problem between trivial and serious has been detected - time to investigate.”
Speculating about the problem is not very useful - for an analogy, when your answering machine has a message you could speculate as to who left it and what it says - or you could play the message and know.
This is the right advice. An inexpensive device that transmits the data via Bluetooth plus a Smartphone app (like this one) make it simple to find the number of the code, which you then Google to get a full description of what’s wrong and how to fix it.
A used car with an active Check Engine light could be ideal for a prospective buyer. You check the code, find out it’s calling for replacement of a $5 part, and negotiate a $500 discount with the (not-very-bright) seller to cover the terrible risk you are running.
This is all great information for me. I’ve been out of cars for a few decades, used to work on them up till about 30 years ago, but never one with an onboard computer. Thanks so much. I’ve been checking out code readers and watching tutorials on youtube. Very interesting all of this. Is this a recommended check on checking out any car, even with no check light on?
Many auto parts stores will do a free scan to determine the code the computer detected. Note that these codes themselves often don’t pinpoint the problem- there can be several reasons a certain code is thrown. But it gives you an idea.
A reasonable seller will allow you to have this done as part of a test drive.
OTOH, I would not waste my time. I assume that the seller has already determined the reason for the fault and the economics of fixing it vs. the value of the car isn’t good. What’s worse, the owner might have been driving for some time with the light on, turning a small problem into a big problem.
The car is for parts or significant work by a really good DIYer. (And based on the OP’s question, the latter is ruled out.)
yes, and this is why it’s important to understand that parts stores don’t do this out of the goodness of their hearts, but in anticipation of you spending hundreds of dollars on (non-refundable) parts trying to fix the problem. The key thing to keep in mind is that reading code(s) is not a diagnosis. A check engine light and DTC is telling you “there’s a problem in this area.” It’s akin to you going to the doctor because your knee hurts. All you can tell him/her is that “my knee hurts.” The Dr. then needs to do however many diagnostic tests to determine if your knee hurts because of a torn ligament, pulled muscle, cartilage damage, bursitis, etc.
for example, a car I had in the past set a CEL P0340 “Camshaft Position Sensor Circuit Malfunction.” Note that it does not say “P0340 Camshaft Position Sensor Bad,” it says “Circuit Malfunction.” That means the fault could be the sensor itself or anywhere in the wiring between it and the PCM. So you go to the parts store, they read that code, and you buy a new CPS and install it, and when you start it the CEL is still there. So not only have you wasted money, you now need to spend more time digging into the wiring harness to look for shorted/broken wires, corroded terminals, rub-throughs, etc.
(in the interest of full disclosure, in my case the fault was a failed cam position sensor, but it was 2.4 liter Neon and CPS failure at about 100,000 miles was widely known.)
Also, most other electronic modules have their own diagnostics and trouble codes, but only emissions related P0xxx codes are mandated by law, and most inexpensive code readers will only look for P0xxx codes. Most cars also have Uxxxx (network) Cxxxx (chassis) and Bxxxx (body) diagnostic codes which will not set a check engine light, nor will most code readers scan for them.
All the above commentary about various technical details is correct as far as it goes. But it misses the larger point.
*The * key decision-making issue for the OP is what city & state is he in? Does that location have emissions checks? What sort of checks?
If not, the CEL and underlying problem is *probably *ignorable. For a while. It may also indicate a car whose fault causes crappier than normal gas mileage. Which may offset the lower price you can get for buying a CEL-on car.
If the OP is in a location with stringent emissions checks the situation changes completely.
If so, now he has bought an unregisterable car with an unknown cost-to-repair before it can be registered. A code reader plus Google, or better yet a local mechanic, can *estimate *how hard/expensive fixing this particular code or codes *probably *will be. But with pretty large error bars. And the bigger the potential repair, the bigger the corresponding uncertainty.
That’s about of like agreeing to buy a used car for some number between $1000 and $4000 based on rolling some dice after you’ve shook hands on the deal. IOW, some people might take that gamble; experienced car people won’t. Getting a mechanic’s inspection reduces the amount at risk, but doesn’t eliminate it.
yeah; a steady CEL without driveability problems is typically not immediately critical. A flashing CEL is.
yep, and you can’t just clear codes and go to the inspection, because they’ll also do a code scan and the PCM will report “OBD Monitors Not Ready” and they’ll tell you to come back after driving it for a while.