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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 15181
Experience:  GM Grand Master Technician 2007. 14 years experience.
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Keeps setting p0446 new vent valve wont run evap test sets

Customer Question

keeps setting p0446 new vent valve wont run evap test sets p0446 and evap purge isnt running only when commanded
JA: How many miles are on the car? Have any warning codes popped up?
Customer: 51127 miles very low no other codes
JA: What is the model of your '49127 Chevy?
Customer: tahoe 5.3l 4x2
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: hoping to fix myself......evap vent valve replaced
JA: Anything else you think the mechanic should know?
Customer: no
Submitted: 5 months ago.
Category: Chevy
Customer: replied 5 months ago.
2001 tahoe 4x2 5.3L
Expert:  Chad Farhat replied 5 months ago.

Hi, I'm Chad ,Welcome To JustAnswer, I'm reviewing your question and I will be posting a reply ASAP

Expert:  Chad Farhat replied 5 months ago.

2001 Chevy Truck K Tahoe 4WD V8-5.3L VIN T

Save Article

DTC P0446 Circuit Description The powertrain control module (PCM) monitors the performance of the evaporative emission (EVAP) system by applying a predetermined level of vacuum to the EVAP system then monitors the vacuum decay rate. The PCM sets this diagnostic trouble code (DTC) if the vacuum decay rate is more than a predetermined value. Conditions for Running the DTC - DTCs P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0443, P0449, P0452, P0453, P1111, P1112, P1114, P1115, P1121 or P1122 are not set. - The ignition voltage is between 10-18 volts. - The barometric pressure is more than 75 kPa. - The fuel level is between 15-85 percent of full capacity. - The engine coolant temperature (ECT) is between 4-30°C (39-86°F). - The intake air temperature is between 4-30°C (39-86°F). - The start up engine coolant temperature and the intake air temperature are within 9°C (16°F) of each other. Conditions for Setting the DTC - The EVAP vacuum decay rate is more than a predetermined value. - The conditions are present for more than 2 seconds. OR

- The vacuum present in the EVAP system is more than a predetermined value. - The conditions are present for more than 4 seconds. Important: This DTC does not report a first failed test. A first fail of this DTC will have a scan tool status as Not Run. 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. - Clear the MIL and the DTC with a scan tool. Diagnostic Aids Important: - Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM. - An accurate indication of fuel level is required for the PCM to properly Pass or Fail this DTC. Always diagnose fuel level sensor DTC's before performing this DTC's diagnostic table. Always inspect for fuel level sensor DTC's stored as History. - The Service Bay Test may have to be performed in cold ambient air temperatures when the vehicle is running a winter grade fuel. The scan tool displays a message when the service bay test does not run. - Inspect for charcoal release from the vapor canister. Refer to the Evaporative Emission System Cleaning procedure, See: Evaporative Emissions System > Procedures > Evaporative Emission (EVAP) System Cleaning Conditions for Running the Service Bay Test

- The battery voltage is between 10.5-17.5 volts. - The fuel level is between 15 percent and 85 percent of the full capacity. - The engine temperature is between 3.5-35°C (38-95°F). Perform a physical inspection of the EVAP system. Inspect for the following conditions: - A loose, missing, defective, or incorrect fuel tank cap. - Incorrectly routed or defective EVAP system vacuum and vapor lines. - A malfunctioning or damaged vapor canister. - Inspect for charcoal release from the vapor canister. Refer to the Evaporative Emission System Cleaning procedure, See: Evaporative Emissions System > Procedures > Evaporative Emission (EVAP) System Cleaning The vacuum and pressure in the EVAP system is measured in inches of H2O (water). Most gauges measure vacuum in inches of Hg (mercury) and pressure in psi (pounds per square inch). The following table illustrates how the values compare:

Expert:  Chad Farhat replied 5 months ago.

1-you need a smoke test , run smoke thru the evap system to make sure no vacuum leaks

2-check evap valve connector for backed out pins ,

3- the pcm initiate the test , so check ground on the evap connector and wiring back to pcm

Customer: replied 5 months ago.
why dont i see duty cycle at the purge valve during test drive with the tech 2
Expert:  Chad Farhat replied 5 months ago.

i dont know you should , are you saying it does not display the duty cycle on scanner right ?

Expert:  Chad Farhat replied 5 months ago.

you said it activate the purge valve on command, so that leaves a leak ,if it want reach correct pressure it want activate ,so smoke test first .

.

Customer: replied 5 months ago.
correct no duty cycle on test drive.......if i command the purge valve on i have duty cycle....increase and decrease....works with a noid light also
Expert:  Chad Farhat replied 5 months ago.

i say do a smoke test , you have a leak, it is working obviously when commanded, so power & ground is good .

I know it has low mileage ,but it is still 15 years old on the electronics and wires , if no leaks and wires good then that leaves you the pcm itself

Customer: replied 5 months ago.
thanks for your help i have alldata pro and direct hit also
Expert:  Chad Farhat replied 5 months ago.

well that is good i have that too:). but it does not change what i told you on what is happening in my opinion :)

Expert:  Chad Farhat replied 5 months ago.

you welcome ,

I know some will give you hard time ,but that is part of our business.

Good Luck

let me know what happens with it

Customer: replied 5 months ago.
Next time ask what is fuel tank pressure sensor readings are 5 volts and -32 mbar tank sensor was bad
Expert:  Chad Farhat replied 5 months ago.

great job you solved it.

you found the magic answer. you can not beat alldata or direct hit .