Service engine soon light
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Joined: Jan 2007
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From: Liberty, NC
Service engine soon light
I guess this goes here. My service engine soon light comes on at 1/4 of a tank of gas. Does anyone else have this problem. After i put more gas in it goes away. Its not a big deal but i need to get it inspected soon.
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Posts: 161
From: Huntsville
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Posts: 1,457
From: Seattle, Washington
I honestly think it has nothing to do with the gas...
...I think it's a code that gets thrown at a random moment and when you pull into the fuel station, the car is off long enough for the PCM to reset and when you start it again, the code doesn't get thrown again thus the SES light is off and when the car is running for a long period, the code gets thrown - hence why it "seems" to be coming on when you have 1/4th a tank of gas...
I had something like that and thought it was the gas aswell however it turned out to be a failing O2 sensor because the PCM doesn't read the O2's until the car has fully warmed up and the PCM isn't ganna throw an SES light unless it fails two consecutive times.. ...you can drive alot of miles before it fails twice in a row...
Get it scanned, you're not ganna pass an emissions test with the light on... even if it's off, if they pull codes and find an old code sitting there then you still won't pass...
...I think it's a code that gets thrown at a random moment and when you pull into the fuel station, the car is off long enough for the PCM to reset and when you start it again, the code doesn't get thrown again thus the SES light is off and when the car is running for a long period, the code gets thrown - hence why it "seems" to be coming on when you have 1/4th a tank of gas...
I had something like that and thought it was the gas aswell however it turned out to be a failing O2 sensor because the PCM doesn't read the O2's until the car has fully warmed up and the PCM isn't ganna throw an SES light unless it fails two consecutive times.. ...you can drive alot of miles before it fails twice in a row...
Get it scanned, you're not ganna pass an emissions test with the light on... even if it's off, if they pull codes and find an old code sitting there then you still won't pass...
Last edited by Need4Camaro; Mar 12, 2007 at 01:07 PM.
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From: Huntsville
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From: Seattle, Washington
Nope, the codes will still be there for the next three times you crank the engine... however in most cases, the SES light will only activate if the same error is reported in TWO conescutive starting periods...
Example of an SES that will NOT activate...
Cause - Engine misfires for the first time
Effect - Code is stored, SES is NOT activated
You turn your car off for 5 minutes... code is still stoored... Drive around again...
Cause - Engine doesn't misfire again...
Effect - Code is stored for 3 conescutive starting periods or 50 miles, however SES is NOT triggered...
-----------
Example of an SES that WILL activate...
Cause - Engine misfires for the first time
Effect - Code is stored, SES is NOT activated
You turn your car off for 5 minutes... code is still stoored... Drive around again...
Cause - Engine misfires again within 3 consecutive starts or 50 miles...
Effect - PCM recognizes the same code is being reported TWICE... SES is activated...
----------------------------
Now below is what throws alot of people off and makes them think that it's just a glitch and nothings wrong with their car...
...Example of an SES that will go OFF and ON...
Cause - Engine misfires for the first time
Effect - Code is stored, SES is NOT activated
You turn your car off for 5 minutes... code is still stoored... Drive around again...
Cause - Engine misfires for the second time...
Effect - SES is triggered...
You drive around some more, say you make 3 stops...
Cause - Engine has not misfired within the 3 stops...
Effect - SES is DEACTIVATED however code is still stored...
Then you crank it up from a cold start next morning... say you have close to 1/4th a tank left after all the driving you've done the day before...
Cause - Engine misfires for the third time while code is stored in the PCM
Effect - SES is reactivated after PCM realises the same code has been reported twice...
It repeats process... thats a rough explanation, it goes far more in debth but I'm trying to keep it as simple as possible...
Basically... the problem has to be a recurring problem over and over again for the SES to STAY on... which can be very tricky for O2 sensors because lets say you take one Long trip and one short trip...
Long trip gives the O2's enough time to heat up so the PCM can read them, If it's malfunctioning, the PCM stores the code however won't trigger the SES... Just remembers it so it will know to look for it again
Your next trip however is too short to give your O2 sensors enough time to heat up and thus, your PCM doesn't look for them.. ...The code is still THERE... However the PCM didn't get a chance to read there was an error meaning you're driving around with bad O2 sensors and your SES light may never come on, you would never realize it...
Then lets say your next trip is 50 miles, O2's easily warm up and give the PCM erratic readings, and triggers your SES because this problem was reported TWICE... Then however you take three short trips and don't give your O2's enough time to heat up to be read, Your PCM doesn't get erratic readings so therefor it assumes their fine... The codes are saved however the SES is deactivated after 3 trips or 50 miles of the error not being reported... but this doesn't mean that you don't have a problem
Example of an SES that will NOT activate...
Cause - Engine misfires for the first time
Effect - Code is stored, SES is NOT activated
You turn your car off for 5 minutes... code is still stoored... Drive around again...
Cause - Engine doesn't misfire again...
Effect - Code is stored for 3 conescutive starting periods or 50 miles, however SES is NOT triggered...
-----------
Example of an SES that WILL activate...
Cause - Engine misfires for the first time
Effect - Code is stored, SES is NOT activated
You turn your car off for 5 minutes... code is still stoored... Drive around again...
Cause - Engine misfires again within 3 consecutive starts or 50 miles...
Effect - PCM recognizes the same code is being reported TWICE... SES is activated...
----------------------------
Now below is what throws alot of people off and makes them think that it's just a glitch and nothings wrong with their car...
...Example of an SES that will go OFF and ON...
Cause - Engine misfires for the first time
Effect - Code is stored, SES is NOT activated
You turn your car off for 5 minutes... code is still stoored... Drive around again...
Cause - Engine misfires for the second time...
Effect - SES is triggered...
You drive around some more, say you make 3 stops...
Cause - Engine has not misfired within the 3 stops...
Effect - SES is DEACTIVATED however code is still stored...
Then you crank it up from a cold start next morning... say you have close to 1/4th a tank left after all the driving you've done the day before...
Cause - Engine misfires for the third time while code is stored in the PCM
Effect - SES is reactivated after PCM realises the same code has been reported twice...
It repeats process... thats a rough explanation, it goes far more in debth but I'm trying to keep it as simple as possible...
Basically... the problem has to be a recurring problem over and over again for the SES to STAY on... which can be very tricky for O2 sensors because lets say you take one Long trip and one short trip...
Long trip gives the O2's enough time to heat up so the PCM can read them, If it's malfunctioning, the PCM stores the code however won't trigger the SES... Just remembers it so it will know to look for it again
Your next trip however is too short to give your O2 sensors enough time to heat up and thus, your PCM doesn't look for them.. ...The code is still THERE... However the PCM didn't get a chance to read there was an error meaning you're driving around with bad O2 sensors and your SES light may never come on, you would never realize it...
Then lets say your next trip is 50 miles, O2's easily warm up and give the PCM erratic readings, and triggers your SES because this problem was reported TWICE... Then however you take three short trips and don't give your O2's enough time to heat up to be read, Your PCM doesn't get erratic readings so therefor it assumes their fine... The codes are saved however the SES is deactivated after 3 trips or 50 miles of the error not being reported... but this doesn't mean that you don't have a problem
Last edited by Need4Camaro; Mar 12, 2007 at 06:28 PM.
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