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How to keep evaporative emissions monitor from running?

This is in regard to a 2002 Daewoo Lanos.

If I use a generic OBDII scan tool to clear the codes, the codes clear, but a new code immediately sets: P1618, and then the engine will misfire a lot, the check engine light will blink while driving, and the transmission won’t shift out of 1st gear.

If I disconnect the battery to reset the computer, the engine runs ok other than a minor miss at idle, and the transmission shifts ok, however the check engine light will only stay off for a short time, maybe 40 miles. Once the evaporative emissions monitor runs, it sets the codes P0442 and P0456. I had two shops which specialize in emissions repair do a smoke test and perform additional tests to find the source of the alleged leak, and neither could find anything. One said the PCM might be defective, the other said without a factory scan tool, they cannot diagnose this further. No one has this special tool.

The problem for me is that this car could really use new front struts, because when I back out of my driveway, unless I go super-slow, it “bottoms out” and the towing hooks hit the road surface. However I cannot justify paying to have that done if I’m not going to be able to get this thing through emissions this summer.

I think the PCM really is defective, however I am concerned that if I get a used one from a junkyard, that will not be acceptable for emissions testing purposes because it will then read the VIN from the junked car.

On the other hand, if I can get all of the monitors to run EXCEPT for the evaporative emissions, then I can pass emissions and renew my license plate.

Any ideas?

If you dont know how to code…and hack… you cant stop it from running. Thats what the ecu is told to do…right down its checklist.

You need to be inside the ecu … in a binary sort of way to alter this. Not to mention it being highly illegal to mess with emissions anything.

That would be my estimation of the situation.


For the evaporitive emissions monitor to run, the ambient temperature must be 95 F or less and the engine must be within 10 degrees of the ambient temperature (cold start). If you start the engine, drive for 60 seconds, shut off and restart, the monitor will be aborted and will not run (engine temp not within 10 degrees of ambient temp). This is for the medium and large leak monitor, I believe this must pass before the small leak monitor (natural vacuum) is considered.


Many cars include amount of gas in the tank in the equation. My toyota will not perform emission leak test unless tank filled >1/4, <3/4. Once I got monitor to complete, I kept tank full until state testing was done. Pesky intermittant leak foiled!


ALL the monitors must run in order for you to pass the emissions test. The test station will know if a monitor hasn’t run.

What you need to do is fix the vehicle.

P1618 mans that some peripheral device tot he ECM is not communicating. The ECM is OK but you might just disconnect the ECM and reconnect, aka reseating the pins, will solve that.

P0442/446 could be a bad gas cap, improperly tightened gas cap or a saturated canister from chronic overfilling of the gas tank. It could also be a defective purge valve OR it could be the peripheral device that is not communicating because the connector is loose, disconnected or just needs reseating.


There are MANY more tests which need to be performed before condemning the pcm

Can the purge valve pull a vacuum . . . ?!

Is a good vacuum supply actually reaching the purge valve . . . ?!

power and ground good at the purge valve . . . ?!

vent valve working properly . . . ?!

power and ground good at vent valve . . . ?!

all fuses related to the evap system good . . . ?!

I could go on . . .

And you have to think of it like this . . . the pcm doesn’t check if the evap system can hold pressure. It checks if the system can pull and hold the appropriate vacuum for the specified time period. Knowing this should affect how you choose to diagnose the problem

Even though the shop you went to didn’t have the factory tool, a smart guy can still go a long way with a wiring diagram, multi meter and a professional level scan tool. Smart guys will figure out a way to supply power and ground to the purge- and vent valves while watching their meter and gauge(s). It is all possible, but you have to be prepared to pay for possibly several hours of diagnostic time

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No one said anything about “hacking” the PCM, or doing anything else illegal. If I had posted a thread asking how to lower the odometer mileage so that I can sell a car for more money, your response would have been reasonable. But I was merely asking for information related to how a PCM decides to run one of its self-tests!

The fact is that according to the letter of the law, a 2002 model year vehicle passes emissions if all of the following are true: the MIL is commanded off, there are no stored trouble codes, no more than one monitor shows “incomplete”, and a visual inspection shows no missing/tampered emissions components.

If someone happens to time disconnecting the battery just right to when they bring their vehicle in for inspection so that it passes, they have complied with the law. If the light happens to come on in a day or a week or a month after passing inspection, that doesn’t magically make it illegal.

This is actually not true. As I stated above, a 2001 and newer gasoline-fueled vehicle is permitted to have one monitor show “not ready” and still pass.

And reasonable efforts have been made to fix the vehicle. P1618 on a Daewoo is an internal PCM fault. Also, it is interesting that attempting to clear the codes with a code reader results in this code immediately setting–when it was not there before–and once set, the car barely runs at all, however disconnecting the battery lets it run ok.

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It is not an internal fault in the ECM (Daewoo calles the PCM an ECM) but a fault in communicating with one of the peripherals. That is external to the ECM. Since you are getting purge valve faults also, there might be a connection issue. Reseating the pins is a valid troubleshooting step.

Whoa…whoa wait a minute … Your original post… If my brain is not completely out to lunch asked the question of “how do I stop xx monitor from running”… Not sure if I’m totally spacing out or if you edited your post. Both are entirely possible.

So in response to my possible hallucination of you asking the question of “how do I stop xx monitor from running”… My correct, albeit equally hallucinogenic response was…to code and hack your ECU…which is what would have to happen to stop a monitor from running aside from unplugging it and starting over (also correct on a technicality, tho completely useless).

I honestly don’t know where or why I responded to that question…If I made it up…or what but I surely thought you asked it.

If not…disregard and let me finish my hallucination @bcohen2010 LOL