Service engine soon light on....


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Old 05-14-14, 04:17 PM
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Service engine soon light on....

I have a 2001 Chevy pick-up with 117,000 miles on it. My service engine light came on, put it on the code reader and it had a Evaporative Emissions code showing. First thing I did was put on a new gas cap and then cleared the engine light. After driving it for about 100 miles the light came back on again, now it won't pass inspection. The vehicle inspection report said "Evaporative Emission Control System Leak Detected (small leak). If it's not the gas cap, were would I look next for the problem....
 
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Old 05-14-14, 04:40 PM
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The vacuum hose that leads to the EVAP. Knowing the exact code number might help us help you.
 
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Old 05-14-14, 07:44 PM
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They have a trouble code on the vehicle report, P0442. Is that the code you need?
 
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Old 05-14-14, 08:09 PM
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Yes, thanks. Possible issues:

- Missing or loose fuel cap
- Incorrect fuel filler cap used
- Fuel filler cap remains open or fails to close
- Foreign matter caught in fuel filler cap
- EVAP canister or fuel tank leaks
- EVAP system hose leaking
- Fuel tank leaking

How it works:
The Powertrain Control Module (PCM) tests the Evaporative Emission (EVAP) system for the following conditions:

- Large and small leaks

- Excess vacuum

- Purge flow during non-commanded conditions

- Fuel Level and Fuel Pressure sensor faults

- EVAP Purge and Vent Valve faults

The PCM monitors the Fuel Tank Pressure sensor in order to determine the level of vacuum/pressure in the EVAP system. The PCM commands both the EVAP Purge Solenoid and the EVAP Vent Valve ON when the conditions are met in order to apply an engine vacuum to the EVAP system. The PCM commands the EVAP Purge Solenoid OFF once the system has reached a predetermined level of vacuum. This test verifies if a vacuum can be achieved in the EVAP system. Failure to develop a vacuum may be caused by a large leak or a restriction.

(Read more: P0442 Chevrolet Evaporative Emission Control System Leak Detected Small Leak OBDII Engine Light Trouble Code | Engine-Codes.com)

You could also provide the model and engine type of Chevy truck. Perhaps that would help us narrow the possibilities down further.

You can also do some of your own research if you like. Often, vehicles will have the same recurring problems, and searching for what others have found can often help you diagnose your problem. You obviously aren't the first one to run into this sort of thing.

I would Google the code, and then your model of truck.

For example: P0442 2001 Chevy Silverado 5.3L

You might find information that would help you narrow down your search. I know that the hoses under the tank that lead to the EVAP or to the gas tank are subject to a lot of abuse from the road- dirt, rocks, etc so those hoses take a lot of abuse. If you can get under the vehicle and follow those hoses from the canister back to the tank and to the intake manifold you might find a hose that's cracked or baked or split/torn at a hose connector. A hose that is suspect will often leave black rubber residue on your hand, after you've run your hand across the hose. Once hoses get to that point, it's often a good idea to replace them.

An electrical problem might also be a possibility and would give a false reading- it would be hard to find. While that's possible, go under the assumption that it's not that.

You can also try Youtube. Type in Chevy truck P0442.

There is an EVAP purge solenoid located somewhere in the engine compartment. The hose leading to this may sometimes vibrate on the engine and develop a wear spot that can eventually lead to a leak in the hose. This is true of pretty much any hose, EVAP or otherwise, so it would be good to check them all closely.
 
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Old 05-15-14, 04:15 AM
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When all else fails find a good independent garage with a "smoke" machine.
 
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Old 05-15-14, 05:48 AM
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You've replaced the cap, so the next step in my book would be to carefully check the fuel tank filler neck and then work your way forward from there.
 
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Old 05-16-14, 12:31 PM
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If you can't find/afford a mechanic with smoke machine, you can use a cheap cigar and blow smoke into the evap line and if it leaks you should see smoke escaping somewhere. Make the smoke as dense as possible.
 
 

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