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Dan, Technician
Category: Car
Satisfied Customers: 24209
Experience:  Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
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Check engine light came..leaking..canister closed valve and gas cap

Customer Question

Check engine light came on after having to go through several flooded streets. Took it to Aamco for their free Check engine light scan, was told the code said something was leaking and to find out what and where, they needed to do a "smoke test" for 75.00. Did that then was told I need to replace the canister closed valve and gas cap which would then cost me about 250.00 for parts and labor. Does this seem all on the up and up? I read so many bad reviews on Aamco that I am almost afraid to trust them with my vehicle.
Submitted: 7 years ago.
Category: Car
Expert:  Dan replied 7 years ago.

The smoke test should have identified the problem and I think you should tell them you expect the problem to be fixed free of charge since they did not fix it when they said that was the problem and you have already paid to have it fixed when it isnt fixed or at the very least I'd tell them I expect all of the labor charges refunded as it did nothing for you. It sounds like the charcoal canister may have gotten flooded when you went through the puddle causing this leak. They can use the following steps to diagnose problem if you bring it back. Let me know if you have questions. Thanks


1. First check the canister-closed valve that is located under the hood by the charcoal canister. Verify that there is voltage on the Black/White wire with the key on; when the Blue/Black wire is backprobed and grounded, the valve closes to seal off the EVAP system vent.

2. Next locate the purge solenoid under the hood by the canister. Verify that there is battery voltage on the Green wire with the key on. If there is voltage, start the engine, backprobe and ground the Red/White wire, and verify that the valve opens and vacuum is applied to the charcoal canister. The vacuum signal may be ported so the engine may have to be off idle for the vacuum to be applied to the canister.

3. If works correctly, locate the EVAP pressure sensor on top of the fuel tank sending unit and backprobe the White/Black wire. The voltage should read approximately 2.5 volts with no vacuum or pressure, and be steady. If the voltage is erratic, check for a good ground and a 5-volt reference voltage to the connector. If the ground and reference voltage are correct, and the voltage is erratic, replace the pressure sensor.

4. If everything tests good, perform an EVAP leak test. Have the voltmeter on the pressure sensor and monitor the voltage, then ground the canister closed valve so it closes. Then start up the engine and ground the purge solenoid so vacuum is applied to the EVAP system and watch the pressure sensor voltage. Draw enough vacuum into the system so the voltage reads close to 1 volt, then stop and see if the voltage starts to increase. If the voltage starts to increase, then look for a leak in the charcoal canister or fuel tank or filler neck and fuel cap.


P0442 EVAP System Small Leak (0.040") Detected

Possible CausesSetting Conditions
  • Canister Purge valve is damaged, leaking or it has failed
  • Charcoal canister or the "catch" tank is leaking
  • Fuel filler cap loose, cross-threaded, incorrect part or damaged
  • Fuel filler cap 'O' ring is missing or damaged
  • Fuel tank is cracked (leaking), or a leak exists in the fuel tank 'O' ring
  • Fuel tank pressure sensor has failed
  • Fuel trapped in the fuel vapor lines due to faulty Rollover Valve or ORVR valve
  • Fuel vapor line(s), fuel pipes or hoses damaged, leaking or missing
  • Leak detection module has failed
  • Purge solenoid has failed (it may be damaged, leaking or sticking)
  • Vent solenoid has failed (it may be damaged, leaking or sticking)
  • PCM has failed

Customer: replied 7 years ago.

I think you misunderstood my question as all Aamco has done so far for the 75.00 is a "smoke test". I brought my car back home without them doing any repairs because they took so long diagnosing the problem and giving me an estimate and I needed my car back.

I also just realised that I am on someone else's computer so don't send a reply to their email address as I won't get the answer.

I will just call around to some local repair shops for an answer instead rather than waste your time or somone elses money, thanks anyway.

Expert:  Dan replied 7 years ago.
I did understand that they did the smoke test....but I'm saying to ask for your money back since the smoke test did not come to the correct problem. I dont send this to any email, it will go to whatever email address you setup the account with. This isnt a simple problem, it will need to be diagnosed by someone who knows what they are doing with the right equiptment otherwise you will be replacing parts until you get lucky. Let me know if you need anything, thanks.