Help with diagnosing P0446 Evap code

Kaz26

Newbie
Original poster
Nov 15, 2021
3
USA
Vehicle: 2003 Chevy Tahoe 1500 LT (with 5.3L V8)

I understand that Code P0446 means the car's computer has detected a problem with the EVAP system vent valve.

I have tested the evap system vent valve. It is open when not activated and closed (holds vacuum) when activated with a 12v supply.

I cleared the code, but it popped back up. Then I got an ELM327 and used Torque Pro to look at the fuel tank pressure (FTP) sensor value. However, it showed: No Data.

My question: why this is showing No Data?
I was under the assumption that the FTP sensor was probably bad so I replaced it. After replacing it, I tried to read it again with the Torque app, but it still says the same thing, "No Data".

Help with this will be greatly appreciated as I cannot smog the car until I sort this out.

Thanks in advance
 

Joe_67

Registered Member
Aug 9, 2022
40
Central Virginia
It's important to always remember that a sensor and or other part that might be related to setting error codes are only parts of larger circuits, and that codes are about the circuits. So, given that you're getting the "no data" message on the FTPS, I'd first want to check the integrity of the wiring between the FTPS and PCM. (I.e., maybe the FTPS and valve are both doing great, but the PCM has no way of "knowing" that b/c the info doesn't get through). If you search around the forum you can find things like the PCM pinouts and other wiring diagrams.
 

10Burb2500

Registered Member
Sep 9, 2022
13
Reading PA
I recently had a similar issue, P0449. Replaced the vent valve, still popped a code. Hooked up a Tech2 to try and command it, it could not see the valve. Long story short and some diagnostics later, the main wiring harness from the PCM was rubbing on the edge of the 3-way plastic bracket on top of the motor, where it first comes up the driver's side of the engine.
It had rubbed completely through the tape and one of the wires and had cut it. Patched the wire, problem solved.

So I would check for continuity from the harness at the PCM back to the valve and/or the pressure sensor.

Alldatadiy was a fantastic help for finding the pins and connector locations on the harness.
 

Kaz26

Newbie
Original poster
Nov 15, 2021
3
USA
It's important to always remember that a sensor and or other part that might be related to setting error codes are only parts of larger circuits, and that codes are about the circuits. So, given that you're getting the "no data" message on the FTPS, I'd first want to check the integrity of the wiring between the FTPS and PCM. (I.e., maybe the FTPS and valve are both doing great, but the PCM has no way of "knowing" that b/c the info doesn't get through). If you search around the forum you can find things like the PCM pinouts and other wiring diagrams.
That makes sense. There is actually another code that popped up with the BlueDriver code scanner, but it is not part of the service engine light codes.

The code is U1016 (Lost communications with Engine Control System)

However, I managed to get the car smogged since all the modules except the Evap cleared with no codes. I have driven it about 500 miles now and the Evap monitor has still not cleared which is interesting. That makes me thing that it isn't even running the test on it now. Or maybe the test just isn't completing.
 

Kaz26

Newbie
Original poster
Nov 15, 2021
3
USA
I recently had a similar issue, P0449. Replaced the vent valve, still popped a code. Hooked up a Tech2 to try and command it, it could not see the valve. Long story short and some diagnostics later, the main wiring harness from the PCM was rubbing on the edge of the 3-way plastic bracket on top of the motor, where it first comes up the driver's side of the engine.
It had rubbed completely through the tape and one of the wires and had cut it. Patched the wire, problem solved.

So I would check for continuity from the harness at the PCM back to the valve and/or the pressure sensor.

Alldatadiy was a fantastic help for finding the pins and connector locations on the harness.

This seems highly probable for my situation as well. Can you possibly take a pic of the area so I can see where it is located exactly? Thank you for the help.
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
23,038
Ottawa, ON
However, I managed to get the car smogged since all the modules except the Evap cleared with no codes. I have driven it about 500 miles now and the Evap monitor has still not cleared which is interesting. That makes me thing that it isn't even running the test on it now. Or maybe the test just isn't completing.
It can take many drive cycles before it sets, which is why it's often exempted from smog tests or is allowed to pass with one test not completed. As long as it has no codes, they usually pass it.
 

10Burb2500

Registered Member
Sep 9, 2022
13
Reading PA
This seems highly probable for my situation as well. Can you possibly take a pic of the area so I can see where it is located exactly? Thank you for the help.

I saved a few pics here:
Doesn't really show where it is, but if you take off the plastic engine cover, the main harness comes up the drivers side of the engine to the top of the intake manifold, and splits on top of a y-shaped plastic bracket. This was right on the edge where the harness makes contact.
 

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