Code Reset Problems

Have a 2000 Mazda Protege that came w/ a 1.8 ltr. engine. Has been changed to a 2001 2.0 ltr. Everytime it’s taken to get an emissions insp. it shows Codes Will Not Reset. No problem codes, just will not reset. What can be done ? I’m getting 5 different answers from assorted garages & the State.

Is anyone suggesting the problem is related to the swap? The simplest answer is usually the correct one.

Yes. The problem seems to be stemming from the swap. I’m getting answers that range from : Remove engine, replace computer, have computer “flashed”, have computer reset, drive car 100 mls. Just don’t know who to trust. Don’t want to spend $2000 on a 9 yr. old car.

Without the matching computer, you will always have that problem.

That’s one really weird problem OK. I assume that your state uses state approved emissions inspection equipment and it is what is reporting Codes will not Reset? Does anything interesting or enlighteneing happen when you try an ordinary garden variety code scanner?

I imagine that the ECU (computer) in the car is the one that matches to 2.0 liter engine, not the ECU for the original engine. If it’s the ECU for a different engine, then emissions test and drivability problems wouldn’t be a surprise, would they? Did all the airflow, and other power control/emissions related stuff get changed to match the 2.0 engine when the transplant was done? If not, maybe you shouldn’t/can’t pass the emissions test.

I’m thinking either a bug in the state approved emissions test equipment (what are you supposed to do about that?) or maybe some sensor somewhere is missing/different because it wasn’t upgraded when the engine transplant was done. Still and all, I’m clearly missing something because in my world view, reseting the codes is a computer function and ought to work even if there is no engine in the car at all.

Maybe a three prong attack:

  1. Get a wiring diagram and make sure that every control and sensor is connected and looks to be appropriate for the 2.0 engine.

  2. Contact Mazda and see if they can offer any advice/information.

  3. Contact the your DMV and ask if they are aware of any problems with their emissions testing equipment that could cause your problem. There is probably intelligent life somewhere in the DMV. Whether you and it can ever get into communication is a different question.

After sleeping on it a bit, I wonder if “Can’t reset codes” might be programmer speak for some “monitors” being not ready. Basically, there are some emissions tests that are not completed and posted until a certain number of drive cycles have been completed. Unfortunately, the definition of a “drive cycle” varies from vehicle to vehicle. Here’s a link to a GM drive cycle description which almost certainly will NOT be the same as a Mazda drive cycle. I just linked to it so you can see what I am babbling about:

By reputation, some vehicle’s drive cycle specifications are fiendishly difficult to meet. A few early OBD II cars (1997 Nissans as I recall) literally can’t complete some of their tests even when they are running perfectly. I once saw a regulation from New Jersey specifying which tests those cars do not have to complete.

Sorry if that is not very helpful. It’s the best I can do.

It seems to me that the trouble has to be internal to the ECU. You could try removing the battery connection for about a half hour to see if that will recycle the ECU. You will reset the monitors if you do that and won’t be able to do an inspection for a while until they set again. If that doesn’t clear the trouble then I would say you need to replace the ECU. You should be able to get a used one for around 100 dollars, just a guess.

The problem is the monitors haven’t been set for the OBDII diagnostics. You’re suppose to use a scanner to check each monitor after a drive cycle is performed. But you can try setting the monitors without a scanner. But in doing so, you must follow the drive cycles to the letter. Here they are.

Mode 1 (PCM Adaptive Memory)

*All accessories off.
*Start engine and allow to up to operating temperature.
*Raise the idle speed to 2500-2700 RPM’s for 15 seconds.
*Raise the idle speed to 3800-4200 RPM’s for more than 15 seconds.
*Release throttle and allow engine to idle for 20 seconds.
*Turn off engine

Mode 2 (EGR Verification)

*All accessories off
*Allow engine to reach operating temperature.
*Drive the vehicle 50-60 MPH for at least one minute.
*Stop vehicle and let idle for 30 seconds.

Mode 3 (HO2C/TWC Verification)
*All accessories off
*Engine at operating temperature.
*Drive vehicle for at least 5 minutes.
*Drive vehicle more than 50 MPH for 1 minute.
*Drive vehicle at 40-60 MPH for 3 minutes.
*Stop vehicle and let idle for 30 seconds.

Mode 4 (EVAP Verification)
*All accessories off.
*Raise idle to 3,300 RPM’s for 200 seconds.
*Drive vehicle immediately.
*Accelerate from idle to 40-60 MPH within 20 seconds.
*Ensure 40-60 MPH is achieved within 4 minutes of intial start.
*Drive at 40-60 MPH For at least 2 minutes.
*Stop vehicle and idle for 30 second.

If doing this doesn’t turn off the Check Engine light, repeat the procedures. If the Check Engine light still won’t turn off, then there could be a communication problem with the computer and the different engine you installed.


Guess I’m an idiot. I should’ve said “Not Ready Readings” to start with. Have tried the drive cycle method twice. No luck. The State of NC has not let me have a tag or 3 day pass to drive the car. So I’ve gotta find a way around that problem. Guess I’ll have to p/u another scanner. Also have tried disconnecting the battery too. Thanks for all responses. Keep 'em coming & I’ll keep trying.

Can you tell us anything about the engine swap? Were all of the original 1.8L engine sensors and valves transferred to 2.0L engine? Which ones were swapped, and which not? Do you know what sensors the 2.0L engine has that the 1.8L engine didn’t have? It’s the things (sensors and valves) that are different, from one engine to the other, that are causing the incompatibility.

Sadly, I cannot tell you anything about it. It was done before I bought the car, so I’m at a loss. Appearance wise, they look the same at a glance. I lived in a “Safety Only” county when it was bought. Then switched to emmissions. We discussed the sensor deal. Just haven’t isolated the issue yet.