[hobbygto65]

Wrong, he has both lights. But it's just the service engine soon light that's on.

[mgarblik]

All I can respond to is what the OP posts here. Read his first line in post 17. I don't own one of these vehicles but service 3-400 late model vehicles every year. I do not know what each of the tens of thousands of individual models has for warning lights which change every year and by each manufacturer. I may have a factory service manual for that Envoy at my college I can look at later. 2004 was the last year GM produced printed manuals. Not sure if we have that one or not.

I just re-read post 17 for about the 10th time. Possibly the OP is saying he has both lights, but only the SES light is illuminated. Bottom line is WE HAVE TO ESTABLISH IF THE VEHICLE PHYSICALLY HAS A CHECK ENGINE LIGHT AND A SERVICE ENGINE SOON LIGHT. It is clear the SES light is the only one illuminated. Again the Check engine light and the SES light CAN be the same light. Depends on year, make, model, options in some cases. I didn't invent this crap, I just have to work on it. SAE and the EPA have done a horrible job standardizing terms, abbreviations, and functions of these warning lights.

[hobbygto65]

I did a little reading and it sounds like if use any scanner other than a GM dealer scanner you won't get a code. Also you may be right the two lights may be the same on this model.

[pont3]

Originally Posted by mgarblik

All I can respond to is what the OP posts here. Read his first line in post 17. I don't own one of these vehicles but service 3-400 late model vehicles every year. I do not know what each of the tens of thousands of individual models has for warning lights which change every year and by each manufacturer. I may have a factory service manual for that Envoy at my college I can look at later. 2004 was the last year GM produced printed manuals. Not sure if we have that one or not.

I just re-read post 17 for about the 10th time. Possibly the OP is saying he has both lights, but only the SES light is illuminated. Bottom line is WE HAVE TO ESTABLISH IF THE VEHICLE PHYSICALLY HAS A CHECK ENGINE LIGHT AND A SERVICE ENGINE SOON LIGHT. It is clear the SES light is the only one illuminated. Again the Check engine light and the SES light CAN be the same light. Depends on year, make, model, options in some cases. I didn't invent this crap, I just have to work on it. SAE and the EPA have done a horrible job standardizing terms, abbreviations, and functions of these warning lights.

Thanks for your efforts, but I was CRYSTAL clear that my Envoy has BOTH, a "CHECK ENGINE" light, AND a "SERVICE ENGINE SOON" light. Only the "SERVICE ENGINE SOON" light is illuminated. The "CHECK ENGINE" light is NOT on.

The "check engine light" came on a little over a year ago. I plugged in my scanner and it indicated that the engine was not reaching optimal temperature, (which is emissions related), and suggested I replace the thermostat. I did that and the CHECK ENGINE light has not illuminated since.

The "service engine soon" light, which has never been illuminated, until now, is what I am referring to. I did pull out the owner's manual and the first thing it says to check is the gas cap.

But I really appreciate your fighting to help me out. Thanks!

[mgarblik]

Perfect! Now we can continue if you like. On your PARTICULAR vehicle, the SES light will store codes referred to as manufacturer codes and turn that light on. They could be emission codes like a gas cap loose, but the codes that will light the SES only are not considered serious enough by the EPA to light the Check Engine light, also called the MIL light after 1996. A parts store can not read the codes, which is why they came up empty. But codes are in there. Generally not serious. You will need an "enhanced scan tool" to read the codes. The GM Tech 2 was the primary GM tool for this but Snap-on, MAC, OTC, Bosch, and dozens of other companies have enhanced scan tools. I currently use a Autell DS-908 as my enhanced scan tool. I also have a GM Tech 2. Either can get the manufacturer codes. I would do that before throwing parts at it although a gas cap may take care of it. As an easy test, take some wheel bearing grease and lube the O-ring real well on the old cap and put it on tight. If the light goes out, you know you need a new cap. Good luck with it.

[poncho-mike]

pont3, I don't remember what code mine was throwing but it sounds like your car and my car have the same issue. The diagnotics list the gas cap as possibly not sealing to the nozzle very well. My check engine light would come and go, even after cleaning the fuel inlet surface with scotchbrite (I put a damp paper towl in to keep grit out of the tank). As mentioned earlier, my problem went away in winter for the last two years, so I inspected my car in March while it was cool. This past winter the light stayed on. My buddy has scanned it a couple of times and it is always the same issue, some type of evaporative pressure issue. I've racked up 50K miles while the light has been on. Since the light stayed on this time, I might not be able to get it inspected unless I fix it.

I should mention this popped up around 200K miles and I fixed it by changing the gas cap. So definitely start there.

[TedRamAirII]

I think this model is famous for a Vent Valve going bad. Wont hold, and leaks vacuum. But I think most any Code Reader would pull it? Usually like a P0440 something. But Purge valves also go bad. Usually leak when commanded off. Maybe a fuel tank filler neck issue? A code will be helpful.

[PunchT37]

Tank vent valves are a common problem.

[400 4spd.]

FWIW, our '03 Envoy only has the "Service Engine Soon". That is what would light up and throw an evap related code when a gas cap was bad. It's worth a shot.

[poncho-mike]

Yes, the code I'm currently showing is a P0440.

I've removed the small DC powered valve at the engine and tested powered it with 12V to see if it clicks, and it worked. My friend also told me to look for cracked flexible lines near the gas tank. He also said there are hard plastic lines going to the back side that can crack as well if you hit something in the road. He said worst case is the charcoal cannister can go bad.

[mgarblik]

The vent valve near the tank and canister are high failure on GM vehicles. The valve is normally open to atmosphere. When the PCM commands the canister to purge vapors, it opens the purge valve which is normally closed and outside air is drawn through the vent valve into the canister and the more dense outside air pushes the vapors from the canister into the intake to be burned. This empties the canister of vapors. The vent valve is only closed during PCM testing of system integrity. The PCM closes the vent valve and opens the purge valve to pull a vacuum on the entire EVAP system. When vacuum level is reached, it closes the purge valve and seals the system and starts an internal clock. It watches the pressure drop through the fuel tank pressure sensor for a period of time. If there is a leak, it will set codes. P0440 is a gross EVAP leak. Gas cap loose or bad seal is the most likely cause. A leaking vent valve that can't seal is next most likely on GM cars. Then the purge valve and finally the hoses, connections and canister. Using an EVAP smoke machine is the most effective way to isolate the problem. To check the vent valve, fill the system with smoke. The vent valve SHOULD be smoking. Then shut the vent valve with a scan tool. The smoke should stop. Fairly simple diagnosis. For people without testing tools, you can start replacing parts and hope for the best.

[PunchT37]

The vent valves are usually full of trash. Especially 4 wheel drive trucks. I’ve seen em packed with mud. Also, the canisters full of water. You can tell. Take em off and they weigh 10 pounds.

[poncho-mike]

So the cannister vent valve and the purge valve are different parts?

[PunchT37]

Originally Posted by poncho-mike

So the cannister vent valve and the purge valve are different parts?

Yep. Purge valve is on the intake usually. Vent valve is on or near the tank. Sometimes connected by a 5/8 ish to 3/4 hard plastic line. Purge valve is always an entry to the intake for a vacuum source.

[Half-Inch Stud]

Scrubbed the EGR path on my 95 Lincoln and walla the MPG went from 18 to 24.

[Matt Meaney]

I believe most, if not all, evap codes are generic (starting with "P0") and will show up on even the cheapest scan tool. the manufacture specific codes (starting with "P1", "B", or "C") might show up on a better tool. all these codes will most likely set off the "check engine", before a "service engine soon" light on a car equipped with both lights.

this is going back a few years, so I don't remember the specific reason. A family member had a 2002 cavalier with both lights. sometime after 105K miles the service engine soon light came on with no code in the ecm. asking a mechanic at the time, he explained that it was in the computer to turn the light on after a certain mileage. the manufacturer wanted a component inspected or replaced due to mileage. then they would reset the light.

the light was never addressed. it would go out and come on periodically by itself. it didn't affect how the car performed and with no code in the ecm memory, it would pass emissions. although, it went to the test when the light was off.

[mgarblik]

Originally Posted by Half-Inch Stud

Scrubbed the EGR path on my 95 Lincoln and walla the MPG went from 18 to 24.

That's a huge mileage increase, but very possible. If the path was really clogged, combustion temperature would go sky high and the engine would try to detonate, the knock sensors would detect this and back up the timing as much as 30 degrees to calm the detonation but kill the gas mileage. I bet the driveability improved as well.