Ok so here's a question... in a different thread I ranted at how the mice pissed all over the overhead console and shorted out the universal remote circuit board. It smoked and glowed a lovely orange. As the board was pretty much melted and not safe, I clipped the 3? wires that power the board and capped them off.

Could that be part of the problem? I'd hate to think that garage door thingy has anything to do with the fuel gauge.

 

The only common denominator might be the BCM. You mentioned the fuel gauge quit, and then the SES light came on. Whatever is causing the short in the fuel gauge, may have also caused a short in the EVAP vent solenoid circuit, (it's in the same harness). Just a guess at this point

This is where a bidirectional scan tool comes in real handy. Plug it in and see if the BCM can accurately control the fuel gauge, and if the fuel level sending unit is reporting correctly to the PCM & BCM. But, that's not an option, so we need to manually test some things.

Check that purple wire, lets see what's going on there. I'm going to have you do three tests on it: Voltage from the PCM, resistance to ground, and resistance from the PCM to the fuel pump module. The results of those three tests should tell us where the problem is.

You said the SES light came on, what trouble code is in memory?

 

PO452 or P0452 Not sure if it's a zero or Oh.
Powertrain - Evaporative Emmisson Control System Pressure Sensor Low Input.

 

Makes perfect sense. The pressure sensor is on top of the tank, right next to the fuel pump module connector. P(zero)452 means low input to the PCM on the pressure sensor signal wire. More than likely the fuel gauge and P0452 are related. Find one problem and the other will be close by. Check the harness for damage from the tank up to the PCM, might be something obvious. May end up checking the pressure sensor wire just like the fuel level sender wire, (open, short etc).

 

If only I had a hoist : - (
I'm not going to be able to do this for a while, probably not until next week sometime.
A friend is borrowing the truck to switch apartments over the weekend.

I assume it's safe for him to drive. I told him to fill it up and to keep an eye on the computer that says how much gas he's used.

I will post back some info next week.

 

ok...I'm back and the blazer is up on ramps. Phew...not a lot of room to work but here's what I've done:

disconnected the harness at the top of the pump.
set blazer to run but not started. Gas gauge didn't wiggle, as before.
found clean spot to touch black wire to body
touched red wire to purple wire in harness = .02 volts, not ~5.

Oddly, I then touched the red wire to the gray wire (positive for FP) and only got .1 volts.

I will add that when I disconnected the battery this winter to charge it...the FP gauge shot to full and then back to nothing the first time I started it.

Will

 

Any thoughts?

 

The fuel pump relay applies battery voltage to the grey wire in the fuel pump module connector for approximately 2 seconds when the ignition is initially turned to the RUN position, then it drops to near zero volts.

The purple wire, (in the same connector), should show approximately 5 VDC when the ignition is in the RUN position. If not, that's the problem with the fuel level sender, (the purple wire has an open circuit).

Both black wires in the connector must show less than 5 ohms resistance to ground at all times.

The PCM uses the fuel level sender data when running the EVAP monitor. If the fuel level sender is not working, the P0452 will likely set and turn the SES light on.

 

Ok thanks. So the purple wire should have approximately 5 volts at the harness where it connects to the fuel pump setup.

because mine does not I need to trace that purple wire back up to the engine compartment and see if I have a broken wire along the way?

 

Ignition in the RUN position, the purple wire should show ~5VDC. It goes from the fuel level sending unit directly to the PCM, with no connections in between.