2003 Blazer ZR2

P0446 Evap System Vent Control Circuit
P0452 Evap System Pressure Sensor Switch A Circuit Low
Gas gauge stuck on empty

So I'm pretty confident replacing the tank pressure sensor would solve part of this but would it be connected to all? Can they be replaced by "touch" instead of dropping the tank or is there not enough room?
Also, I know it's best to only use Delco fuel pumps, but what about just the sensor? Not having any fuel delivery issues so the pump seems fine.

comments, suggestions, insights welcome. Thanks,.

 

The fuel pump is not involved in these evap system issues with the possible exception of its top plate seal to the tank but not the pump operation.

A proper functioning evap system requires a good gas cap seal. Make sure its clicked closed. A lot of people start with a new cap because its easy and a relatively cheap fix.

Absent success there, the question is why is the PCM getting an incorrect pressure reading signal during the routine evap system testing?:

Pressure sensor failure
Pressure sensor wiring
Pressure sensor 5V reference circuit or ground
An evap vent valve that wont close fore testing
A leak elsewhere in the system hoses, etc
A purge valve that will not stay closed for testing. This would lead to engine performance issues.

The "correct" way to address this is to check the sensor wiring, and quality of the 5V reference and ground but that's tough because of the sensor location. I don't know if you can get to the sensor with the tank in place, maybe another member can help here.

Check to see if the evap vent valve is closing when commanded.

Smoke test the evap system to look for leaks.

A more practical approach for weekend mechanic might be:

Gas cao as mentioned
Evaluate the evap valve and the quality of the hoses, cannister and connections.
Lastly, evaluate the pressure valve wiring and reference signal and replace if necessary.


George

 

So I changed out the tank pressure sensor. (Thankfully I didnt have to disconnect the tank from the fuel lines) - no change. I still need to trace the wiring harness from the sensor to see if there are any visible issues.
Installed a new evap vent solenoid - that cleared the P0446, but not the P0452

Noticed I have a leaking fuel filter - is that something that can trigger a P0452?
If not, I suspect it's in the fuel pump. Still have a dead fuel gauge, so I'm thinking the float is toast as well.

 

That pressure sensor is a three wire sensor meaning it uses a 5V reference. One quick check of the wiring is to measure for the 5V reference between the gray wire (5V ref level) and the black wire (lo ref or signal ground). That is not a chassis ground, it is a clean signal ground from the ECM so don't load that ground with anything strange, it may not be protected at the ECM.

Your P0452 code means that either the pressure sensor, its wiring, or the PCM are bad or an actual pressure/vacuum leak exists somewhere in the evap system. A shop would do a smoke test on the evap vapor circuit to look for leaks. You will have to resort to a visual inspection of all of the hoses/clamps, and the charcoal canister. you have replaced the pressure sensor and evap vent solenoid so lets assume for now that those items are good. The only thing left is the wiring, leaks, purge solenoid and the gas cap (a cheap and simple thing to rule out).


George

 

Oh, forgot your last question:

Bad fuel pump would not be involved. A leak at the top gasket where the pump attaches, yes that could be involved. The fuel leak, not sure on that one but I suppose if the leak is big enough and disturbs the the tank pressure enough then maybe,


George

 

Thanks.
Well, I can rule out the gas cap, that was the first thing I replaced.
Pump gasket appeared in good condition when I swapped the pressure sensor.