P0453 Porsche fault code 99 - Tank pressure sensor

[txhokie4life]

This one's got my goat.

I swapped the fuel pressure sensor from another car (unfortunately the donor
doesn't run -- so I can't be 100% it was good) but I get the same
code. And shortly thereafter a CEL.

there are 3 terminals to the plug.

if I mock up some sort of connector,
what resistance values does the FPS normally send out?

My next check will be to ohm out the wires -- but I hadn't gotten that far.

any help/pointers would be greatly appreciated.

Mike

[Wayne 962]

Hi again. I think you'll find the answers here to be spot-on. Anyways, I'm not aware of any fuel pressure sensor on the Boxster fuel injection system - I'm sure that you mean the tank vent line pressure sensor (996-606-205-00-M14) that sits on the vent line and measures pressure in the tank. The code that you mention here says:

P0453 Tank Pressure Sensor - Short to B+

Which may indicate a wire harness fault? If you unplug the sensor, do you get a different code? I have a hunch your sensor is probably okay, but there may be a wiring fault somewhere.

More info, and I can help further...

-Wayne

[txhokie4life]

tore into it this evening.
confirmed the code can be removed -- but as soon as KOER, code appears
via duramatic. It takes some time before the CEL hits.

I pulled the battery and got access to the tank pressure sensor.

I was able to pick up 5.4V on Bl/Vi, 0.4v on Br/Pk and 0.4v on Re/Vi, with KOEO
with KOER I get ~6.2v

I think the 0.4v was just a gnd differential off the battery.

Disconnecting the sensor still gave me the P0453.

I tried to ohm out the connections to the DME connector
but none of them seemed to ohm out -- so not sure what was
going on there -- but obviously there must be some connection
or I would not get the 5v.

Very Frustrating -- probably operator error.

I hooked up the DME again
then I went back to the front of the car and
looked at things a little closer.

Note the color code for the 5V -- it's the Bl/Vi -- but that is labeled
on my schematics as the Pressure Differential --
this should have been on the Re/Vi not Bl/Vi.

I'm assuming that the Sensor Pressure Differential M660 is
the right one.

It's almost as somewhere the connections are backwards.

Seems hard to believe.

I considered rotating the connector upside down -- but it is keyed (probably for good reason) to only be inserted one way.

I didn't have the heart to cut the wires and swap them without
considering other alternatives or proving out the connection
back to the DME.

But I ran out of time and patience -- ok patience first ....

fortunately when I put everything back together -- I was exactly where
I started -- at least I did no harm.

thx,

mike

[Wayne 962]

Hi Mike. I think you may be missing the obvious - that the sensor is working fine, and that there is a pressure leak in your gas tank system. You might want to try emptying your tank (just let the car run down really low), and then disconnecting one of the fuel line connections (both inside and outside the tank), and pressurizing the tank to see if there is a significant loss of pressure somewhere. This might be as simple as a worn out gas cap seal?

-Wayne

[txhokie4life]

I'd be happy with the obvious -- I think :-) until I have to
replace something really expensive that is :-)

I was just going down the list of P0453 things
which all point to issues with the sensor or wiring.

Will try that next.

Still a little confusing about the voltage on the wrong wire.

I also thought about creating a resistor divider to set the voltage on the differential and
see if I could make the DME happy just to eliminate from the wiring harness back.

Seems like what I've read it wants ~2.5v which is a pretty easy divider -- or I can just use a pot to set the value.

BTW,
thanks for your help

Mike

[Wayne 962]

The kicker on what you said originally is that you already swapped out the sensor with another one. It's unlikely that they are both bad. It is likely sensing a fault with your system.

-Wayne

[txhokie4life]

I was thinking about the perceived mis-wiring last night after I buttoned
it all back up.

Pulled up the schematics again -- but noted there was different
schematics for years 97, 98 and 99.

I had thought that 97-99 were the same.

Interestingly enough -- the 98 and 99 are the same for the tank pressure sensor,
but the 97 is different.

Well turns out that this is a 99 Boxster that we transplanted a 97 engine.
I'm darn sure we used the 97 engine wiring harness.

I'll have to sit and study those schematics closely and retrace my steps and see if I can reverse engineer what is what.

Any idea where connector X3/1 BLACK is located??? *** I think I found it in the diagrams -- rear trunk, drivers side 15cp (I'll have to verify this)

oh the joy!

mike

[Wayne 962]

Part Number 996-606-205-00 fits all cars from 1998-2004, and is attached to the vent breather line. I'm assuming that's what you're talking about here? Can you post a picture just to make sure?

As far as I know, the engine wiring harness is not what plugs into this sensor - I believe it plugs into the main chassis harness (at least it wasn't there on my 2000 Boxster engine harness).

You're talking about the sensor located here, right?



That's no where near the engine wire harness...

-Wayne

[dad911]

Originally Posted by txhokie4life

Well turns out that this is a 99 Boxster that we transplanted a 97 engine.
I'm darn sure we used the 97 engine wiring harness.

I'll have to sit and study those schematics closely and retrace my steps and see if I can reverse engineer what is what.

Any idea where connector X3/1 BLACK is located??? *** I think I found it in the diagrams -- rear trunk, drivers side 15cp (I'll have to verify this)

oh the joy!

mike

x3/1 Black is in the trunk, left of the DME.

The fact that you are getting different voltage readings, leads me to think that the sensor & wiring work, and the problem may be pressure in the system? Perhaps a hose was pinched or leaks during the engine swap?

If you still have the spare sensor, what happens if you plug it in to the harness, but not install it in the tank?

[Wayne 962]

Originally Posted by dad911

The fact that you are getting different voltage readings, leads me to think that the sensor & wiring work, and the problem may be pressure in the system? Perhaps a hose was pinched or leaks during the engine swap?

I agree (as I mentioned above). The sensor is there to detect a problem with the system. Most of the time the sensor is good, particularly when you plug another one in and it acts the same...

-Wayne

[txhokie4life]

Or at least I think I got it.

No CEL nor any engine codes with duramatic. (prior to fix it showed up as soon as I cleared it with KOER.

It was the 97 Engine harness that was the culprit.

The 98+ have an AAV Valve and a different Tank Pressure Sensor. 97 seems to combine these into one function.

Not that it is likely anyone else will run into this, but who knows?

Here is what I did:

From the BODY HARNESS:
For the life of me I could not get the round pins out, so I ended
up old school splice, twist, solder, tape.

X3/1 -- Ye/Br Pin 12 Connects to Ye/Br Pin 11 (Engine Harness Side)
X3/1 -- Br/Pk Pin 22 Connects to Br/Pk -- I found it on another connector and spliced it (Gnd Reference)
X3/1 -- Re/Vi Pin 1 Connects to +5V, DME 53, I found it in the harness
and connected it where there was a junction of 8 others.
X3/1 -- Bl/Vi Pin 11, Connects to Pin 11 (EHS), but then you have to connect
pin 72 on the DME connector. I used the jumper to pin 43, left it open
and connected it to pin 72.

To open up the DME connector -- undo screw far side, pull out weather stripping,
undo zip tie, remove cover, push/pull far side out, there is a catch on near side
such that it comes out far side first.
I used a paper clip (thanks Wayne!) -- took some patience put the pin released,
and it was easy to put back in.
To put it back together -- insert near side, be careful not to pinch any wires and
continue the reverse of above.

Hopefully a couple days driving and passing the Emissions test will prove it all worked out fine.

Mike (fingers crossed)

[Wayne 962]

Cool! The 1997 cars were very much like any other early car in a series - they had a bunch of one-off stuff on them that wasn't often carried forward to the later cars. Another example is that some of the early 1997 cars had non-programmable DMEs.

Glad to hear that you worked it out, and it's archived here for everyone else in the future!

thx,

Wayne

[gus969]

Well I just bought a 1997 Boxster and I don't have a tank pressure sender or a purge valve on my canister.

My car has a 1999 996 engine in it and it's throwing these codes:

PO447 **** off Valve activated

PO453 Tank Pressure Sender

I guess it's looking for something that's not there.

Maybe the DME is not programmed properly?

[Terry Worick]

Hello,

I have a 1997 Boxster I'm converting to 3.4 as well giving the same 2 codes. I'm using the stock 2.5 wiring harness w/ a 98-99 ECM reprogramed to 3.4 specs.

I made the addition of the wiring for the resonance flap to the 2.5 wiring harness and added the solenoid and that is working correctly. Every thing else seems to be in order.

I would like some input on wether the early 97 cars have this valve and sensor?

Thanks

[xmac911]

gus969 and Terry,

I know it is 2 years later after your posts, but were you able to figure out how to fix these 2 codes?

[DMadigan]

If you look at my post "Air at fuel test port" you can see the tank pressure sensor in the line at the top of the picture. That is the sensor that I had to replace the wires on.

[xmac911]

Thanks DMadigan.

I am in the situation with Terry where I have a 1997 with a transplanted 996 3.4 engine. The car does not have the pressure sensor nor shutoff valve at the carbon canister - nor the wiring to support either. The ECU flash is the culprit due to the 3.4 engine starting from 1999, is looking for that hardware that is missing.

I am trying to figure out how to emulate the sensors to the ECU to clear the errors.