Check Engine Light on a 98 Toyota Corolla

I'll go along with Jeff in his suggestion that you make sure your gas cap is REALLY tight, by ratcheting it a few times extra, and driving it a couple of weeks to see if the light goes off. It's a common problem and has happened to me....and cost me an hour's labor ($88) to tell me to tighten the gas cap.

When my "check engine" light came on in my '98 Corolla, it had a very simple solution: the gas cap wasn't on tight enough. Make sure it's on tightly - until you hear it click, & see if that happens to take care of it.

Cathy

Lots of the consumer auto parts stores will send a person out to the lot to read the code while you wait.

I didn't know that. Thanks!

Do not take the advice of anyone who tells you to replace a part without first checking the part because they generally have only a rudimentary understanding of automotive systems. Proper diagnostic procedure it to CHECK the part before replacing it, or you may end up wasting a lot of money, and IMO, VIP did you a favor by not attempting to diagnose something they are not capable of diagnosing.

All 3 codes can probably be diagnosed in an hour or less at a Toyota dealer, and they generally will apply the diagnostic fee towards the repair if you have it done. Your car will not pass an emissions inspection with the check engine light illuminated so you need to get the problem fixed before you take it in for an inspection.

I don't recommend investing in a code scanner if you are not familiar with automotive systems. They will give you codes but they will not tell you how to check a component or tell you if a component is working properly or not. For example, do you know what a throttle position sensor is, what its function is, where it is on the car, and how to test if it is good or not? If you are fairly handy, you can invest in a Haynes or Chilton's repair manual, or if you are more than fairly handy, you should invest in the factory service manual. You can get some basic repair procedures at

I had experience with a garage that didn't understand the problem but attempted to fix it anyway. My company car started to always hesistate on acceleration, which I thought was due to a weak fuel pump, clogged filter, or bad pressure regulator. I wanted to take it to the leasing dealership for repair, but the new manager insisted on using a nearby Pep Boys instead. They scanned for error codes, did a tune-up, put in new plugs, wires, cap, and rotor and wound up fixing nothing. The mechanic who worked on the car didn't seem to understand when I asked him if there were any abnormal computer readings that didn't generate error codes because he said that if no codes were generated, it meant there were no abnormal readings. I wasn't allowed to take the car to the dealer until I got a refund from Pep Boys, but fortunately they refunded the charges with hardly any argument. The dealer said that the car needed a new fuel pump, and that made the hesitation go away. .

And to add my 2c:

I would suggest to use Q-tip, spread 2-3 oil drops on gas cap gasket, fill the tank, "make sure your gas cap is

REALLY tight, by ratcheting it a few times extra, and drive it a couple of weeks to see if the light goes off."

Good luck, Mike

mack wrote:

Not bad advice, but that won't make the OP's check engine light turn off.

I doubt if a mechanic working at Pep Boys would be able to interpret the raw readings from the sensors and computer, even if they had the proper equipment to do so. He is correct that in that if there are no error codes, then there will not be any abnormal readings, since abnormal readings is what sets error codes.

The primary function of the check engine light is to warn drivers that an emission control system is not working properly, and there are systems in the car that, when malfunctioning, can cause noise or drivability problems without making the car out of compliance with emissions. The fuel pump and fuel pressure regulator are an example, as is the starter. To diagnose the fuel pump problem, a technician would have to connect a fuel pressure gauge to measure fuel pressure, measure fuel pump delivery volume, check voltage at the fuel pump, and then check to see if the fuel pump operates when voltage is applied.

That is like clearing an EKG when someone is in the early stages of a heart attack to see if a real heart attack develops.

IIRC, P0120 is set if a problem is detected once, while P0441 and P0446 have

Pun intended?

I believe that the OP has 2 problems to diagnose - TOPS and a VS. for the evaporative emissions system.

Since I spent a pretty fair amount of time visiting dealers in New England, I can recommend some good ones ;-)

Where do I find the OBD II connector or would one of the devices I buy have instructions on how to connect it? I don't mind buying one, because I'm a techie and I like toys. Also, I would buy a cable to hook my laptop up to it, but my laptop does not have a serial port. :\

The OBD II connector is under the driver's side of the dashboard. The port looks like the port for a parallel printer cable.

If you want to get one to hook up to your laptop, autotap.com has a scanner that hooks to a computer's USB port. OBD II software that runs on the laptop is great if you know how to interpret the signals from a particular sensor and know if the signals are in or out of spec.

The hardware will have instructions on how to connect it, but it is very simple. Plug the device cable into the OBD II port and turn the ignition switch to the on position.

The diagnostic connector under the hood is for stuff like checking ignition timing.

The connector under the dashboard is the one for the OBD II scanner. The connector shsould be very straightforward; sometimes it is under the cover with the fuse panel.

You're welcome!

"The most troubling code I've seen from this poster is the one about the throttle sensor. "

Jeff, what's the worst that could happen with the "Throttle / Pedal Position switch A circuit "? In your opinion, what's the more pressing matter- rear struts or the circuit? Thanks.