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Check engine light on until car is warmed up. No code

I have a 96 Honda Civic CX. The check engine light came on the other day while it was raining (dont know if the rain had anything to do with it) and now it comes on every time I start the car until it warms up. Once in a while it comes back while driving but thats rare. I tried to get the code with a cheap reader and it didn’t show that anything is wrong. I then took it to an auto parts place and they used one of their nice readers to scan it and told me that everything is fine. What’s the next step? Thanks in advance for your help.

I forgot to mention that I also changed the spark plugs and wires, as well as tested a different gas cap which I know works.

Do you have it checked/scanned when the light is on? There’s really no way to know what is causing the light to go on unless it is actually throwing the code while being scanned. Otherwise it could be any of a hundred things… loose or bad gas cap, loose wire, bad catalytic converter, oxygen sensor going out, any of a dozen bad sensors, etc, chipmunks or rats nesting in the engine somewhere, etc, etc. If you have a couple months until inspection, I would just drive the heckout of it until the light becomes steady. Then, you have something to test.

Even thought the CEL is out, the ECU may still store the trouble code. Take it to an AutoZone to have the codes read or rent their scanner and read the codes at cold start-up and post them back here so we can help. Otherwise its just a WAG on our part.

The CEL turns on with the key in “on” but the engine not running, right? Then when you start the engine, while it used to go out immediately, it now stays on for a while. And you’ve checked for codes using two different methods and no codes are stored? Is that all correct?

hmmm … my first guess is there’s a problem, short likely, in the wiring harness that is powering up just that particular dash bulb. When things are working correctly only the engine computer can turn the CEL on, but if there was a wiring short, most likely under the dash area, it could turn on without the computer even knowing it was happening. Has there been any work done under the dash, like replacing a clutch or brake master cylinder?

Yep that is all correct.

I got the car somewhat recently and haven’t done any work in that part of it except for messing with the power outlet which was loose. I tried to tighten it without taking off the bottom of the dash but that didn’t work, so I ended up removing the bottom middle part of the dash to tighten it. Is it possible that I messed something up when I was doing that? How would I check?

I’ve considered this myself but thought it couldn’t be the root of the problem because the CEL goes out when the car is warmed up but I’m pretty new to cars which is why I’m here asking these questions.

The thing that’s confusing is that since the CEL is turned on by the ECM (Engine computer), and it only turns it on for an important reason, there should be a corresponding diagnostic code stored in ECM memory if the ECM is turning it on. W/no code stored, the logical conclusions are

  1. The ECM isn’t turning it on; or
  2. Either that or the ECM is faulty.

For 1, I think what I’d probably do if I had that problem on my Corolla and look up in the FSM wiring schematic which wires are used to light the CEL bulb. Then I’d monitor the voltages on those wires with an in-cab DVM as I was driving the car on a daily basis. If the ECM is turning the CEL light on, I"d expect to see something either close to battery voltage or ground. One or the other in other words. If there’s an intermittent short I’d more likely see voltages varying between battery and ground voltage, intermediate voltages like 7.5 volts vs either 0 volts or 12 volts in other words.

For 2, you’d probably better serve yourself by taking the vehicle to a shop that specializes in Honda or at least Asian cars; someone who has the Honda scan tool. Based on the test results they may temporarily replace the ECM to see if the problem goes away or not.

I have a 1999 Honda Civic EX, which is pretty similar to yours. A few days ago the check engine light came on. (Honda’s owners manual calls it the Malfunction Indicator Light). Per the manual, I checked that the gas cap was on tightly. The manual said if the problem has been fixed, it will take 3 driving cycles to turn off the light. My hunch was the MIL was on for a spurious or very intermittent issue. I disconnected the battery overnight and sure enough, once I hooked up the battery again, the MIL was off. It has not come back on with several driving cycles since then.

Couple things:

If you unhook the battery, you need to know the radio’s code and key in those numbers on the radio to get it to work again. I bought my car new and wrote this code in the back of my owners manual and on the file folder I use for this car.

If you changed spark plugs and then the MIL started coming on, that’s a clue. Did you use the exact plugs recommended in the manual, gapped correctly, and did you seat the plug wires firmly onto the plugs? Has oil leaked into the plug wells? Are the plug wires OK and correctly routed?

Your car has older OBD-I system for storing trouble codes. You can read your stored trouble codes (if any) by using a wire between two terminals on a connector under the dash. The codes will show up as a pattern of blinks of the MIL (check engine light.)

Hey, sorry for not responding sooner. I had some things come up and was unable to try to fix this problem. The car still drives completely fine and not giving any codes. I am pretty sure you are right about it being a short somewhere, most likely the CEL itself. How do I test the current? My guess is remove the ECM and test the wires going in and out of it. Is that correct?

Intermittents are very difficult to find. I’d leave well enough alone.

If the car works perfectly and there’s no code, for a 96 Civic I’d probably do what Bill said above, just live with it. Are you certain you know how to check for diagnostic codes? Have you ever been able to retrieve one before from that car? If not suggest you do something that will definitely post a diagnostic code, like disconnecting the engine coolant temp sensor maybe. That should post a code, and you should be able to retrieve it. If not, I think the problem may be the method you are using isn’t actually coughing up the codes stored. I own a Corolla of similar vintage, OBD I, and it is not obvious how to retrieve the codes, even if you have the factory service manual in front of you, as the method to do it is quite confusing and varies depending on whether it is configured as an automatic or manual transmission. To get it to spit out the codes I have to step on the gas pedal, believe it or not. But the FSM instructions are very non-specific about whether or not that is required or not. Before doing anything drastic, like removing the ECM, make sure you know how to read the diagnostic codes on your car. This may be an opportunity to get connected with a mechanic who knows how, and can show you. As long as you don’t have to pass any emissions tests, another idea is to put all this on hold for now, until an actual drivability symptom appears. Best of luck.

Its the OBD2 system so its pretty simple, just plug in the scanner. Unplugging a sensor and seeing if that throws a code is a really good idea. I’ll do that to make sure I’m actually retrieving the codes correctly. Thanks for that. One thing I found the other day is the evap hose that attaches to the bracket for the gas filter was unattached and facing down. Because of this it was not able to vent. It looks like there is a lot of condensation in the hose when I reconnected it to the bracket so that it faces up. Maybe that could have something to do with the CEL. We’ll see. I just want to make sure I have the car as well as possible because I’m going on a long trip in a couple of weeks. The CEL is the only thing that’s bothering me. I’ve taken care of everything else.

Yup, I fully agree.
If you rent a code reader, it should be even capable of storing data and downloading it onto your computer (if they also provide the disc with the proper program with it). You can then do a much more in-depth analysis. But even just seeing the codes while the engine is cold should be a great help.

1996 was around the time of the obd i/ii transition, so if your car is obd ii, you should be set. Unplug a sensor you know will turn on the cel and should set a code. If you can’t see that code then with your reader, you probably have a reader compatibility problem. Try another one.

Something like that will almost always set a code in newer cars, b/c the evap system is critical to federal emissions standards. With a 1996, don’t know. Even in newer cars, evap codes can take a certain amount of drive time before they set though.

1996 was the first model year that OBDII was mandated in all cars. The OP’s '96 will store codes.

So I did manage to get a code when I unplugged the coolant temp sensor. I also took it into a mechanic and he said everything is fine, drove it and ran a diagnostic. Basically came to the same conclusion as we did: there is something up with the wiring somewhere, and it’s not actually effecting the car. This is good news because I’m about to go on a long road trip. It would be great to get the bulb to turn off but I guess thats a future project. Maybe I’ll just put some tape over it for now.

There’s an info how to get the error codes—>

That’s for the OBD1 system. Mine is an OBD2, all civics 96 and newer have obd2.