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Does anyone know of an easy way to disable the check-engine light for a bit?

I have a vehicle that I'll be selling soon. A couple of months ago, the check-engine light came on. I took the car to the dealer, and they said the codes were 300 and 302, which mean misfiring cylinders. I spent $500 to have a number of minor repairs completed (sparkplugs replaced, etc).

This week, the light came back on. I stopped by an AutoZone for a CheckEngine diagnostic, and the same codes came up as before. Since 60 days have passed, the dealer won't check the car for free, even though they clearly didn't fix the problem.

The car runs perfectly, so the Check-Engine light is just an eyesore at this point. Still, I think it will scare away buyers, even though nothing is wrong w/ the car. Do you know of a way to disable that light?

UPDATE: This is an old question, and I've moved on. I left the Check-engine light as-is, and traded the car in to a (different) dealer; I needed a bigger car for a new baby. I took a hit on the trade-in value because of the check-engine light, but I'm okay w/ it. (I added this as a comment too).

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Step 1. Take to dealer (hopefully with a printout of of the autozone diagnostic). Step 2. Proceed to yell loudly at the customer service representative. In all seriousness, check your state warranty laws, they may be required to honor service for longer (just not offer a free "check") so if they didn't do their job they should fix it. –  crasic May 13 '11 at 17:43
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Sounds immoral, unethical, and possibly illegal to me. –  Tester101 May 13 '11 at 19:50
    
IANAL, but this sounds like fraud to me. There is something wrong, or the powertrain controller wouldn't be throwing fault codes. –  Mark Johnson Apr 2 '12 at 13:33
    
This is an old question, and I've moved on. I left the Check-engine light as-is, and traded the car in to a (different) dealer; I needed a bigger car for a new baby. I took a hit on the trade-in value because of the check-engine light, but I'm okay w/ it. –  WEFX Apr 2 '12 at 14:03
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How to disable the CEL is a valid question and there are legitimate reasons to clear codes, particularly after a repair. The OP's motives are irrelevant, really. Calling him immoral, unethical, illegal, fraudulent doesn't answer the question. –  geoO Jun 9 '13 at 10:06
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2 Answers

up vote 9 down vote accepted

To answer your question: Tools that check the code normally can also clear them (some handheld ones are cheap). However they only stay cleared until the next warm up cycle that takes the measurement. (Note: emissions testing machines will realize if the code has been cleared and if a good measurement has not yet been taken).

However, the bigger problem is this is completely unethical. Instead of hiding the engine light, tell the truth. Show the dealership invoice and explain the situation. The car might be "running fine" but the dealer did not fix all the problems or created new ones. The check-engine light is not an eyesore, it is an indication that either something is wrong with the engine/system or that a sensor is malfunctioning.

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Also, if the problem doesn't reoccur, normally a fixed number of key/startup cycles clears the code. –  Doresoom May 13 '11 at 17:13
    
@Doresoom on some cars Unplugging the battery for 10-20 minutes can clear the codes. –  crasic May 13 '11 at 17:41
    
@Doresoom ... and the radio security codes and everything else. :-) Make sure you have that radio code handy... –  Sean Reifschneider Jun 4 '11 at 7:00
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In a US car made after 1996 (and 2008 with a CAN bus) the check engine light (CEL) appears after a specific set of parameters are met with respect to vehicle sensors, generally having to do with emissions performance. This is why cars with CEL lights illuminated automatically fail emissions testing in many jurisdictions, including New York and California.

Possibly the CEL is illuminated for a reason that does not affect drivability, but only emissions performance. In any case I only endeavor to answer your question not judge your motives.

To turn off this light it a simple matter to use an inexpensive code reader plugged into the OBD II diagnostic connector (that is mandated to be located within 2 feet of the steering wheel) and reset the light using the controls on the device, which vary by brand. Some auto parts stores will perform this service or the code reader can generally be purchased for less than $100.

Two caveats:

One, the OBD II will now report that the car is in an "unready" state and attempting to pass an emissions test in this state will cause the car to automatically fail despite the CEL being off. A retest will be required.

Two, driving the car through various "trip" cycles will provide enough data to the car's computer to make the car "ready" but also will cause the CEL to illuminate again if the underlying trouble is not addressed.

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