Check engine light NEVER comes on

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

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

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

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

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

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).

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.

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.

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?

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.

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.

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.

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.

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.

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.

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.

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.

UPDATE - Problem solved!!!

Nevada you were dead on right!!! I finally pulled the glove box out today to have a look at the ECU. At first I didn’t see anything wrong. But as soon as I pulled the top connector off, there it was. The Green/Red wire had been snipped.

I decided that the simplest fix with the lack of space was to crimp spade connectors on. Problem solved.

Now I have light.

The best part is in came on like it should then went out after i started the car. My father in law took his scanner back so I am getting one next week and replacing the o2 sensors as im sure they are original.

Thanks again to all the responded, and especially to Nevada who was dead on.

Someone pulling a fast one, huh? :slight_smile:

Sounds like a good idea to me…The spade connector gives the owner complete control over the nag light…