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2005 Forester X: I have a P0453 code (Evap system pressure sensor / switch high) preventing me from passing inspection. I may be wrong but it seems like that Fuel Tank Pressure Sensor (FTPS) is on top of the tank and to access it im supposed to drop the fuel tank to get to it... and that looks like a beast of a job ... so im trying to diagnose this to death before I launch a laborious solution.

CUTTING TO THE CHASE...
Id like to identify the signal wire of the FTPS and read its voltage.

Can anyone help with:
1- pinout for the connector to the FTPS (including wire color)
2- a pinout of the connector under the rear passenger seat.
3- a pinout of the ECM for this model vehicle (which might give me a place to measure signal voltage and identify wire color)

ALOS: Has anyone cut an access door between the two stock access panels to approach the FTPS from the top-side?

BACKGROUND STORY SO FAR:
I live in the Rust Belt of Central New York and dropping the tank will produce an endless supply of broken bolts and crumbling brackets so I need another solution.
I think that this code means that either the Fuel Tank Pressure Sensor (FTPS) is bad OR there is a short in a wire or a connector. There are two access panels under the carpet behind the back seat for access to the fuel pump. the FTPS is rumored to be on top of the tank between these panels. I can see through the passenger side access panel a bundle of wires that come from the center of the tank but I can't see their source. I have removed the electrical tape and can see four wires they are Yellow/green (x2), Black/green, Brown/yellow. The FTPS should have three wires (with function = source, ground and signal ... I think the FTPS source should be 5 v and the signal should be between 0-5 v with atmosphere pressure (fuel tank pressure with gas cap off) around 2.3-2.7 v (would love authoritative confirmation of that if available)). The four wires that run in this bundle turn up in a big connector that is under the rear passenger seat. I have tested their voltage to a ground source and they all read 13v with the engine running - but they may have nothing to do with the FTPS.

Any other thoughts?

Thank you in advance for your help!
 

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2009 Legacy
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I have never had to deal with that code but found this in my 2005 manual.
Let me see if I can find the section on removal of that sucker.

526240

Edit: some more stuff related from the service manual.
526241

526242
526244
526245
526246


That item 34 certainly looks like the part you're after. I've taken fuel pumps out by means of an access cover in the trunk but don't think it gets you enough space to get to anything else..
I wonder whether you could drop the tank slightly, just enough to give yourself a little whiggle room to get some tools through that fuel pump cover so you can remove it. If that was my situation, I'd try that..

.. or break out the a can opener.

In a pinch - like you are, having to pass emissions - maybe hack that sensor with a potentiometer to make the system believe all is well...
..Just long enough to pass emissions, that is.. ;)
 

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Discussion Starter #3
You are the best! Thanks for all the diagrams and technical data. I like how your thinking! You may have suspected that was my Plan-B based on the need for a pinout and a wire color into which I may be forced to introduce some alternative data. I'm not great at reading the circuit diagram. Does that diagram indicate which lead is the signal wire? Is the junction of r57 and r15 beneath the passenger side of the back seat (is there a reference of those connector locations) .

Thanks again for all our assistance - very helpful
 

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That harness comes in on the passenger side of the tank near the front corner. I just dropped mine to fix the vent valve and that sensor might be accesable if you drop the tank on top of the sub-frame. I'm not sure how much room that will give you to go through the access panels, but its worth a shot.
526271
 

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2009 Legacy
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@Bruce S No, it just indicates where it goes into the ECM, unfortunately.

You could put a multimeter on those three legs. If I had to guess, one is likely ground, one + and the third signal. That + signal is most likely 12V because there wouldn't be a lot of room for measurement if they made that voltage 5V - but check anyway.

Then I'd try putting a potentiometer across the ground and + with the runner going to signal. If the ECM 'likes' >4.8 volt, I'd start setting it in the middle and see what that gets you. At 12V, the runner (ie signal) would be about 6V so that would satisfy their criteria. If + equals 5V, you may want to set it to the top of the range.
I can't imagine the potentiometer value to be cricital. They are looking to measure a voltage that likely doesn't need to drive any current so a potentiometer of 10K would do. 10K to ground at either 5 or 12V draws very little current so is safe to the rest of the electronics.

Unfortunately radio shack has gone by way of the dodo but you can get potentiometers on line.
 

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Discussion Starter #6
@fawndog Thanks for the picture. It is super helpful. It looks like there is a secondary cover directly above the sensor. Were the tubing connection (a vacuum hose?) that connect to the sensor buried under that cover. I just measured the space between the bottom of the tank and the sub frame = 2.5 finger-widths.

If you still have that tank on your garage floor ... could you identify the wire colors that come off that sensor so I can locate them at the other end of the harness at the connector that is accessible under the back seat?
Thanks again - your guys are really helpful!
 

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@Remco Thanks for that feedback - that will shorten my trial and error time. Ill be on this project this weekend so this winter-rat can go back to college with my son after Thanksgiving. Radioshack may be gone but I have a great electronics shop nearby that is run by hard-core hobbyists that is way better. Those fellas are awesome. I bought parts for a simulated catalytic converter there and they predicted what I was doing based-on the resistor and capacitor I asked for. Ill report back what I figure out.
Thanks again.
 

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Discussion Starter #9
Update:
Cutting a hole in the floor to access the sensor from the top was pretty easy. The hardest part was removing the seat so I could begin cutting. Here are some pictures of the surgery. In the first picture I have stuffed a few old hack saw blades to provide some cover between my cutting wheel and the gas lines beneath. (just a precaution).
IMG_0156.JPG


In the second picture I have opened up the floor and you can see the sensor in position.
526815


The wire harness for this sensor has three wires. The 5 v reference wire is red. The signal wire (middle wire) is red with a yellow stripe. The ground wire is green with an orange stripe. The Part number is 22627AA280
526816


The sensor connects to the tank with a short piece of rubber tubing.
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There is a steel nipple on top of the tank that the sensors rubber tube connects to.
526819


The other end of the three wires from the connector are part of the big connector that is under the passenger side back seat.
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526822


We tested the continuity of the of the harness from the sensor to the connector and the 5 volt supply wire. We could not demonstrate any voltage change on the center signal wire so we are ordering a new sensor. These sensors are running about $250 at parts stores .... unless you buy direct from China. There is an ebay store that offers them at $35. It might take 3 weeks for it to arrive but I'm gonna try it. Ill post again once I get the part and install it.
 

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@Bruce S WOW! That's quite a write up! It will come in useful for someone in the future.
Good job.

Edit: Not sure whether you weld but you could put the old panel back in place using these butt welding clamps. If you weld, you just tack it back along the seam but should you not weld (or not want to weld near a gas tank), you could use them to keep it in place and seal it all with some automotive seam sealer and leave the clamps in place. Handy for next time it needs to come apart. :)
 
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