Gas Caps and SES Light

willfxp · October 12, 2003

Is the Service Engine Soon ( SES) light supposed to come on when you drive around with out the gas cap on? First time I've ever forgotton to put it back on. But I thought the light would come on to remind me...

I'm wondering if maybe my SES light is busted? I did have a problem earlier (earlier post too), but it went away. I thought maybe the problem fixed itself. Now I am wondering if maybe the light is dead. It goes on for a second while the engine is starting (key in the start position).

Any ideas?

Thanks!

sjspor · October 12, 2003

For the SES light to come on with the gas cap off or loose, it has to fail the diag it runs twice. There are bunch of parameters that have to be met also for the diag to run. Usually if mine goes off, it's either right away or about 20 minutes after I have been driving. I have been setting P0440's for a while now. The light should clear itself

after 3 or 5 succesful diag runs. Though it seems spastic sometimes.

Any one have a clue on how to get the vent valve out of the truck?? Thats the one

attach to frame rail, you can see it on the drivers side between the bed and cab.

SportyShorty · October 12, 2003

My SES light has been on for alomst 5 months now and everytime it pulls a PO440 code. Stealership wants it for a day to do their nitrogen test on it to find where the leak is. I havent brought it in in fear of what they are going to charge me to do it. I've already tried a new gas cap so I'm guessingg that isnt it. Anyone else have a cure for this??

sjspor · October 12, 2003

Sporty, I'm betting my P0440 is the vent valve, mine is intermittent. There must be some dirt or water in it that is keeping from closing all the time. But I can't get it out of the truck. It has to come off the bracket it's on, and I hav'nt figured it out yet.

If yours is a solid bug, then you may have a connection from the purge valve on the engine, back to the EVAP canister.

Good Luck..

frdfandc · October 13, 2003

I think that evap valve you are talking about is the one I had replaced 4k miles ago on my 03 z-71. Its an updated part, and it is supposed to come with a new bracket.

Sporty, as far as your truck goes, with it being a 1999, and it probably having over 36k miles, you will have to pay for a diagnosis unless you have an extended warranty that covers emissions parts.

ctoliver · October 13, 2003

P0440

DESCRIPTION

The EVAP LARGE LEAK TEST is based on applying vacuum to the EVAP system and monitoring the rate of vacuum decay. The Powertrain Control Module (PCM) uses the input from the Fuel Tank Pressure (FTP) sensor in order to determine the rate of vacuum decay. At an appropriate time, the PCM turns the EVAP canister purge valve ON (open) and the EVAP canister vent valve ON (closed). This allows the engine to draw a vacuum on the system. At a calibrated time or vacuum level, the PCM turns the purge valve OFF (closed), and tests the system vacuum. If the system is unable to achieve the calibrated vacuum level, the PCM will set DTC P0440.

CONDITIONS FOR RUNNING THE DTC

DTCs P0107. P0108, P0110, P0112, P0113, P0115, P0117, P0118, P0121, P0122, P0123, P0125, P0443, P0449, P0452, P0453, P1106, P1107, P1111, P1112, P1114, P1115, P1121 or P1122 are not set.

The system voltage is between 10-18 volts .

The startup (ECT) engine coolant temperature is between than 4-30°C (39-86°F) , but the start up ECT is not more than 8°C (14°F) more than the startup IAT temperature.

The startup (IAT) intake air temperature is between than 4-30°C (39-86°F) , but the start up IAT is not more than 3°C (7°F) more than the startup ECT temperature.

The fuel tank level is between 15-85 percent .

The Barometric Pressure (BARO) is more than 75 kPa .

The Vehicle Speed Sensor (VSS) is less than 75 mph .

CONDITIONS FOR SETTING THE DTC

The EVAP system is not able to achieve or maintain vacuum during the diagnostic test.

ACTION TAKEN WHEN THE DTC SETS

The control module illuminates the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails.

The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC

The control module turns OFF the Malfunction Indicator Lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

Use a scan tool in order to clear the MIL and the DTC.

DIAGNOSTIC AIDS

Use the EVAP pressure/purge diagnostic station in order to pressurize the EVAP system to aid in locating intermittent leaks.

Move all EVAP components while testing with the Ultrasonic Leak Detector.

A temporary blockage in the EVAP canister purge valve, purge pipe or EVAP canister could cause an intermittent condition. To repair a blockage in the EVAP system refer to Evaporative Emission (EVAP) System Cleaning. See: Emission Control Systems\Evaporative Emissions System\Service and Repair

willfxp · October 13, 2003

Ahh... thanks for the info!

99silveradoz71 · October 14, 2003

Had the light on the dash go on my 99 and sure enough it was the vent valve.

sjspor · October 14, 2003

So has anyone actually removed the vent valve, I can't get it off the bracket, and don't have enough room to do anything with the valve on the bracket?