Check engine light NEVER comes on

Gaoan

I have a 2000 Toyota Camry that has a unique problem. The Check Engine light NEVER comes on even when first starting the car. I have access to a scanner and know that the car periodically throws a catalyst code but the light never comes on. I just assumed that the bulb was burned out.

Today while solving a non-working clock issue I had to take the instrument cluster to get to the clock. While I had it out I decided to check the Check Engine Light bulb. It looked fine so I took I replaced it with a bulb that I knew worked fine. Again, nothing. The bulb doesn't light at all. About 4 weeks ago my timing belt broke while driving (thank god for a non-interference motor) and it threw a code for the camshaft position sensor but again the light never came on.

Anyone have any idea as to why the light never comes on?

Caddyman

I would be everlastingly thankful...Apparently you don't have to pass an emissions test so it's not an issue.. But if you just can't stand not having that light come on, you could purchase a new dash cluster and ECU ($$$$$$$$) and MAYBE that would restore the cherished CEL ....

kizwiki

http://www.ehow.com/how_5752265_identify-warning-lights-toyota-camry.html

Your light should come on according to the above link when you set the key to the II position, along with other dashboard lights, and be the one light remaining on after a few seconds. If the rest of the lights come on, but the CEL doesn't, and if you bought the car used, the plastic display cover might have been painted with black paint to hide the light, a sneaky old trick to sell a car with a problem. Otherwise, honestly, I have no idea. I'd suggest using the scan tool on as regular a basis as you can manage.

Gaoan

I thought maybe it might be covered, so when I had the cluster out and removed the bulb I was able to very clearly see the symbol with daylight shining through. I know of that trick and thought that might have been an issue. But no.

Although here in Virginia we don't have emissions tests we do have a yearly inspection and an illuminated MIL is cause for failure. So I not that worried about it, but would like to figure it out. With access to the scanner I can clear it before the inspection.

Other than that issue the car runs great and still gets 34mpg on highway with 210,000 miles and the original clutch.

Tester

When turning the ignition switch to the run position the Check Engine light should come on. This is called the self-test mode for the computer. If the Check Engine light doesn't come on in the run position it means the computer failed the self-test mode and there's a problem with the computer.

Tester

Caddyman

When it comes time to sell your car, this feature is worth paying EXTRA for...

Gaoan

Caddyman, you certainly are full of useful and insightful wisdom aren't you

Gaoan

Thanks Tester for the useful knowledge! Very much appreciated!!!

cigroller

Of course, there's also the small matter of wires. Those things in between the computer and the lightbulb.

circuitsmith

You need to find out which pin on the connector to the engine computer is for the CEL.
Then check for continuity from the lamp socket to the computer connector.
Also one pin of the lamp socket goes to ground, check this continuity too.
If all that checks out then it's a problem in the computer module (lamp driver).

Cougar

Like others have already stated, the CEL light is usually turned on through the ECU which probably makes a ground connection inside the unit to turn on the lamp. You can check to see if there is voltage on the lamp lead going to the ECU. If there is about 12 volts on it you should be able to ground that point and turn on the lamp to verify the rest of the circuit is ok. If the ECU is causing the trouble you can purchase a rebuilt unit for a lot less money than a new one from the dealer. This is a fairly common trouble. I have fixed some in the past by replacing the lamp driver IC inside the ECU.

Benji

Well, well, well, well,.....(think 'A Clockwork Orange'), well, well, well!
I have an '05 Camry that has a CEL that never shuts off. I can change the oil and a day or two later, it never fails to come right back on. A knod for consistency. I've had it for six years now without any other noteworthy issues. Dealers and others have shown me the key, switch, steering cloumn,... key, switch, steering column trick to shut it off, and, oh yes, that works,...for a little while. Maybe twenty four hours...a little tounge in cheek here please. But then it is right back on to keep me company again. It does shut off from time to time completely randomly (everybody's gotta eat I guess), but never for long.
I know this is the inverse of your problem but it is interesting to see the results of bigger companies relying on multiple vendors for the same component and it's sometimes many sub-components. Ya never know what ya gonna get. BTW, Click & Clack, my older brother and I were changing engines in my dad's side yard back in the early seventies in Burlington, MA. My dad however, grew up in Your Fair City, in East Cambridge on Spring St. back when men were men and cars needed constant attention.

Gaoan

Thanks guys. the warning lights on a 2000 are right on the circuit board for the cluster and don't have seperate sockets with leads on them. One day when i am feeling adventurous again I will pull it out again and check for continuity with my tester and check the ecu as well. The scanner i have access to is my father-in-laws and he gets kind of ansy if I keep it for too long. This car is in great shape with 210,000 miles on it and still has the original clutch. Ive done a lot of work to it myself including the timing belt a few weeks ago and now have challenged myself to see how long i can keep it running. So that being said, since I can't always use the scanner, I would like to have the CEL working if feasible just so i know whats going on. This past weekend I was able to fix the non-functioning clock that hadn't worked since i bought the car 3 years ago from a friend. found a post on Toyota nation about the exact problem. turns out one of the flat resistors had popped up and the solder had cracked. Just heated it up and reflowed it.


That leads me to a question to Cougar, can you tell me more about fixing the lamp driver IC?

cigroller

Simple code readers are not that expensive & you can pick them up at most any auto parts store. I'd just get one and leave it in the glovebox. Pop it on once in a while & have a look.

Cougar

Subaru clocks have the same trouble and it is a very common problem with them. A one watt surface mount resistor becomes desoldered due to excessive heat on the joints. As far as I know, once the joints are resoldered the problem doesn't come back. I can only assume the solder used at the factory isn't of good quality.

As far as replacing the lamp driver in the ECU it is fairly simple thing to do if you can get the replacement part. You can locate it on the board by following the trace on the PC board that ties to the pin for the lamp. Hopefully something else is wrong with the circuit and it will be easier to fix. The ICs I replaced controlled more than one device so they had multiple outputs, four I think.

keith

It takes more than just not having a CEL light if the inspection station plugs in a code reader. It also takes more than just having no codes. Your code reader also has ready lights which means that the circuits have been checked. You need all ready lights on to pass inspection. Clear all codes, drive at least three drive cycles and check the codes and the ready lights. You may not have all ready lights after three cycles, but if you have none, then the ECU is bad. I vote broke wire though.

Nevada_545

The wire from the ECU to the insrument cluster may have been cut to put the light out. If you didn't see a cut wires behind the cluster remove the glove box and check the green/red wire from cavity #6 of the top connector (E7) in the engine ECU.

If you check this wire with a volt meter or test light note that the ECU provides a ground to illuminate the light.

Gaoan

Thanks again guys. All good points. I planning on getting my own scanner or software for my laptop cig roller, but now the problem is overcoming the urge to fix a minor thing just for the self-satisfaction of saying I could do it!!!.

Keith in the 3 years I have owned the car the light has never come on. I have had to clear a catalyst code on a few occassion. My guess is the O2 sensors have never been replaced. So the codes have been cleared probably 6 times. Most currently being 2 weekends go, and I checked it again this past weekend so there have been more that 3 cycles.

Nevada you make a good point. I will pull the cluster again and check for a cut there as well and also check at the connector at the ecu. If no cut wire, then I'll let go of the issue and move on. Again I enjoy the satisfaction of fixing something that I never worked on before.

keith

Since you have at least 3 drive cycles, you should go ahead and plug in the scanner you have access to. In the display, usually across the top, there are several two letter acronyms, like CC. These are the ready lights. You can also keep pushing the down arrow on some code readers and after displaying any codes, it will scroll through the ready lights one at a time with an up or down arrow indicating its status. It will also tell you if the MIL should be on or off. MIL is the check engine light circuit.

keith

I think Nevada could be right about a cut wire. Toyota's are prone to a P0420 code that is very difficult to get cure, even if you replace all the components in the system. I suspect that they set the detection level a little to sensitive in the computer program. I know of a dealer that could not solve it no matter what they did.

Cougar

Instead of possibly wasting time removing the cluster I suggest you first try grounding the lamp pin at the ECU. If the light turns on then you have proven the trouble is inside the ECU. If the lamp doesn't work then you need to check out the lamp circuit wiring further. One side of the lamp leads should tie to power through the ignition switch and the other side ground through the ECU.