2003 2DR Blazer ZR2 4WD

Well, I don't know if there have been a spate of lawsuits in NC or something, but it seems lately if your vehicle isn't in pristine condition, no mechanic will touch it because of "potential liability." So looks like I'll be doing everything myself from here on out.
First up - Evap codes. I've got P0446 Evap System Vent Control Circuit and P0452 Evap System Pressure Sensor / Switch A Circuit Low with a fuel guage stuck on empty. This has happened before and it was found to be a wiring issue, which was repaired a couple of years ago, but seems to have returned. I suck at electrical diagnosis and have no idea where the previous damaged wire was, so I guess it's time for a crash course. As I recall it didn't require dropping the tank. Welcome suggestions on where to start first while I continue reviewing stickies.

 

Attachments should get you down the right path.

 

Thanks for those, that's a huge help. Does anyone know precisely where on the vehicle that splice pack 422 is located? Or connector 104?

I'm a complete novice when it comes to electrical diagnostics, but am I reading the codes and chart correctly in that the P0446 Evap System Vent Control Circuit is a problem with the white reference/signal wire between the PCM and the Vent solenoid? And that the P0452 Evap System Pressure Sensor / Switch A Circuit Low is referencing the Blk/Wht wire connection from the FTP sensor to the splice pack S422 (Since the fuel pump seems to be workng fine, I would think the wiring beyond the splice pack going back to the PCM would be ok)? Or would the dead fuel gauge indicate a problem also between the Sender Assembly and the PCM, possibly also around that S422 splice pack? Or would a stuck open vent valve automatically screw up the level sensor if there is no pressure being built in the tank? The last time this happened, fixing the bad wiring for the evap codes automatically fixed the fuel guage problem.

Note: The fuel pump/sender is 2 yr old Delphi and the vent solenoid and FTP sensor are both 2 yr old OEM replacements.

 

Clear both codes and see which comes back.

P0446 is a functional test (not electrical). It cannot set if a P0452 is present.

For P0452, the PCM is seeing less than 0.1V on circuit 890. For this code to set, there is no output from the pressure sensor being seen.

At the pressure sensor connector (connector disconnected), you should have 5V when measuring between terminals C and A. Now plug in the sensor and measure the voltage between terminals B and A (or simply use a scan tool to look at fuel pressure sensor voltage output from the sensor. If you don't have a scanner that will read the voltage, then you will need to make 3 jumper wires so you can to connect the pressure sensor to the connector for the second test (and still have access for the meter to read). DO NOT poke holes or otherwise break the wiring insulation to make a test connection. Moisture will travel up the wire to the PCM and corrode terminals, and you are starting underneath the vehicle.

Attached are the locations of S422 and C104, but I think you do not really need them to diagnose this problem.

Best wishes for a successful repair.

 

Unfortunately my cheapo Ancel scan tool doesn't read sensor voltage. I need to find a better one. Any recommendations for good consumer level tools with those features that wont break the bank? Would be nice to have one that could run vent/purge tests too.
As I recall, I got the P0446 before the P0452 originally.

Cleared the codes and it was the P0452 that came back.

Probably unrelated, but is anyone familiar with this ground strap? Photo is taken through the rear driver's side wheel well looking toward the back. It appears one end it bolted to the rear crossmember, but the other end is frayed and unconnected to anything. Filler neck maybe?

 

So go ahead and check the voltage with the connector unplugged from terminal C to A. If you have 5V, then a good share is of your circuits are proven OK - and either your pressure sensor is bad, or signal back to the PCM on terminal B circuit is not making it. Easy-peasy! At least it's not intermittent!

 

Ugh, that's going to mean dropping the tank. Ok, I'll see what I can do.

 

You might want to check the length of the harness forward from the pressure gauge for damage, if you say it has been repaired before. See attachments in post #4. Anywhere between the pressure sensor and the PCM.

 

So just for the hell of it, I fed a wifi scope up over the top of the tank to see if there were any obvious problems before going through the trouble of dropping the tank. Oh yeah. Looks like a rodent or something got up there. Chewed off half the loom and tape, and I can see nicks in the dark green signal wire from the FTP sensor. Going to take a wild guess that's probably the problem. What guage wire is that back there?

 

probably somewhere between 18 and 22 gauge. Pretty small.