Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Passing emissions with unrelated OBD codes

Hopefully this is in the right spot. I have a 2002 Hyundai Sonata and I have to renew my tabs by the end of the month and my emissions are due this year. My check engine light comes on periodically, but usually goes away once I turn my car off. So of course the other day it decided to stay on permanently. I got it checked with an OBD scanner, and my codes were P1529 and P0715, which is something with a transmission control module and a speed sensor, nothing to do with actual emissions.

My question is can I still pass emissions with the check engine light on even if the codes aren’t related to emissions? Do they even check what the codes are?

I’ve tried to look on my states website, and they gave pretty vague instructions about OBD codes, and I tried calling my emissions station but I couldn’t get a hold of anyone. I’m sure each state has different rules, but I’m just wondering if anyone has had luck with a situation like this.

The light did go off for a while after checking the codes, but today it came back on for good. So I’m also wondering if I should just reset the light with the scanner and try emissions anyway.

One problem with resetting the codes is that the monitors are also reset. During the driving to get the monitors to complete the PCM is probably going to run across the root cause of the original code. Most emissions stations will not pass a car with uncompleted monitors.

You should probably have someone troubleshoot the system the code references and get the problem fixed.

Hope this helps.

A call to the emissions office, or try it and see. You usually get a window for repair or dollars spent.

A speed sensor is pretty easy to replace on most vehicles so why not just get it fixed?


If you show up with the check engine light on, you will fail

A code that commands the check engine light on results in a failure, whether the light is on or not

So, if for some reason your bulb is burned out or missing, and you have a code which commands the light on, you will still fail

I suppose emissions requirements vary from state to state, but in Washington state you will fail.

The P0715 IS an emissions related code. Also your transmission is not working properly. If it were, the light would not be on.

P0715 indicates a problem with one of the sensors in the transmission. When the sensor is failing the light comes on. Also, your car will not shift into overdrive at that time. Hence the emissions failure. With no overdrive your engine is revving higher than it should at moderate speeds and probably emitting more grams/mile of pollutants than allowed.

P1529 simply indicates that the transmission controller has detected a fault and requested that the engine controller turn on the engine light. Fixing the other code will fix this one too.

1 Like

This varies state by state. OP might post the state in question.

In any event, OP should telephone the state agency in charge of emissions testing. The phone number is probably on the web site the OP already has found. Here in Calif it is difficult to get a definite answer to this kind of question for some reason. But if you are persistent you can usually get an answer eventually. If all else fails, call your local district’s elected state representative and get their staff to help you. I had to do this one time with a DMV problem, the DMV was completely uncooperative to my plight, and the staff of my local state senator there worked it out with the DMV straight away. Don’t wait until the last minute, this takes several weeks or even months time

For what it is worth, California passed my car with a oil level sensor code set. This code does not illuminate the light and is obviously not emissions related.


Thank you for making my point for me

A code which does not command the MIL on is not a problem, as I stated

Any code which commands the MIL on will result in a failure, even if it doesn’t seem to be related to emissions

Without knowing the state, we are just spinning our wheels.


Yes, the code probably would get called an “emissions violation” in the more jack-booted states, but that’s baloney.

A tranny fault that prevents a timely upshift might result in slightly more gas burnt overall, but it has nothing to do with how cleanly it burns. ATs don’t produce emissions unless something’s tragically wrong.

To call that an “emissions issue” is like saying driving with the windows down or with a suitcase on the roof is a violation of the Clean Air Act.

Even if the code had noting to do with emissions the light being on is a problem in itself.
If another problem crops up that IS emissions related you’d have no way to tell because the light is already on.

While most people equate their state’s testing as “passing emissions”, many states in fact are doing both an emissions and SAFETY inspection. If you notice, the lamp is not called an emission failure lamp. Hereabouts, if the lamp is on, you fail. If they retrieve the current status and you have unready monitors or a set code (but not enough times to illuminate the indicator), you still fail. Most malfunctions can ultimately be considered safety issues.

Some states will allow one or two codes or unready monitors and still pass your car. It varies greatly based on the municipality governing the testing. Without that information, you might as well argue about the color orange…

@meanjoe75fan, you can think it’s jack-booted baloney, but what you and I think isn’t relevant. The poster has to pass an emissions test and his engine light is on. The fact that the engine light is on means that it is an emissions related failure–that’s the only reason the engine light will be on. Non-emissions faults are not allowed to turn on the engine light. Whether you or I call it an “emissions issue” doesn’t matter. Federal regs say it is, and those are the rules we have to play by.

Emissions testing hasn’t much to do with how much gas is burned, but what comes out of the tailpipe. In this case, without a sensor reading the transmission will keep the car from engaging overdrive and may even put the transmission in fail-safe mode, allowing only 2nd and 3rd gear. Now a car driving down the freeway at 4000 rpm will put out more exhaust as measured in grams per mile than the same car driving at 2000 rpm. Hence the emissions failure.

@lokimonster, don’t spend too much time worrying about this. Simply go for your smog test. If you pass, great. If you fail, have the car repaired.


If you prevent that “timely upshift” . . . you are driving in a lower gear, meaning you’re turning more rpms, meaning you are using more fuel, meaning you are polluting more

That is the reasoning

Years ago, I was working on cars that had the MIL lit up because of a faulty upshift delay. Upshift delay comes into play with a cold engine. It keeps the automatic transmission in a lower gear so that the catalytic converter warms up quicker

That was just one example

So, in my opinion, the transmission does have an effect on emissions

Not true. I’ve passed diesel trucks many times with check engine lights on. They don’t run the codes on them, they just look for opacity on the exhauset coming out of the tail pipe.

I have no idea why you’re responding to this old thread, after 3 years

Anyways, in my neck of the woods, if you go for a smog inspection, and your check engine light remains on at idle, you fail

End of story

But what do I know . . . I just happen to perform smog inspections in California, probably the strictest state of all. Both the newer plug-in test, dyno-run and two-speed idle

For the record, the comments YOU made . . . are you talking about smog inspections for diesel-powered light duty vehicles, or opacity inspections? They are not the same thing, and different standards apply. I also perform opacity inspections, btw

1 Like

I agree with this recommendation. Might’s well fix it.

Whether you’ll pass depends on how your state’s inspection regulations are written. Your state’s DMV is who the question should be addressed to.

There’s a theory at work here that OBDII systems are designed NOT to help repair your vehicle, but rather to ensure compliance with federal emissions and safety mandates, and thus any fault code constitutes a sensing of the system that something is in error that is or may be creating a noncompliance. Inspectors won’t parse through error codes to let some go and fail others, That would create a system too subject to the inspector’s subjective opinion, and that would not be a fair system.

Transmission related emissions failure … hmm… didn’t there used to be something called TCI or TCS (presumably transmission controlled ignition) e back in the 1970’s carb’d cars which modified the ignition timing depending on what gear was being used? For emissions purposes?

Modern cars have Transmission Control Modules, and carbed cars had a Vacuum Modulator for the tranny that basically was diaphragmatic and controlled tranny shifting via vacuum from the engine, but ignition timing is and always was controlled by engine demand. In the old days it was done using a diaphragm on the carb that reacted to engine vacuum, in modern cars it’s all done by running the engine demand sensors through an algorithm in the ECU. I believe there was a “middle phase” in the evolution of this process that used carbs to meter the fuel and engine demand signals to control ignition timing, but I cannot think of an example.

To the best of my knowledge, transmissions have never in any way controlled ignition timing. Others might be able to correct my assumption, and specific examples or links would be appreciated.