I am still working on P0453 Fuel Tank Pressure Sensor Input High. My question is specifically about the wiring. The wiring diagram shows FTP sensor like a variable resistor:

PCM---SPLICE 137---(WIRE A, BR/W)---vvvvvvvv---(WIRE B, GY/R)---SPLICE 138---PCM
And another wire connects to the midpoint of the resistor. This wire (WIRE C, R/PK) goes straight to PCM.

I know the three wires are V REF, SIGNAL (INPUT), and SIG RTN (pcm provided). But I cannot tell which is which. My best guess is the SPLICES are V REF and PCM ground, and WIRE C is SIGNAL. But I am not sure. By the way, signal is 4.98 V. Signal wire seems to be shorted to V ref. If not, ground may be missing. If not, FTP itself is bad. Thanks for your help.

 

I don't know if this will help but the 5 volt supply from the PCM is a floating supply, meaning the negitive side is not at chassis ground.
Do not rely on a measurement from VREF to ground because it will not be correct.
Observe the + and - to see which one is the return. The neg is return and common to a number of sensors as is the positive side. A fault here could affect all sensors fed from this supply and be a big hassle until you recognize it.
The lead that goes back to the PCM is the sense lead to tell the PCM what is happening in the circuit and sensor output.
With the above in mind, be carefull to recognize when you see a fault.
One reason the 5 volt supply is floating is to guard against the PCM getting false info from the sensors if there are any ground loops such as at cranking when there is a lot of current flowing on the chassis as well as interference from ignition and other outside sources etc..
Good luck.

 

Thanks for the explanation, Bluegrass. It turned out to be, I mean so far, the V ref wire was cut off at the connector right underneath the air intake. It got pushed down a little too far too many times. On my way to a junkyard to get the same connector. Will report back.

 

That's great to hear a result like this from testing and knowing what is supposed to be and finding the reason why it is not.
No 5 volt feed and sensors just don't feed any signals back to the the PCM.
Good luck.

 

Thanks, Bluegrass. You were correct. Vref was not cut. Put a JY connector. Scanner now reads FTP signal 2.7 V. All fixed, yeah! Advice from this forum kept me from giving up.

I got tired of relying on OBDII code and had to buy a scanner. Cost me $360 but it saved me time and frustration. No more guessing or part-throwing.

I had to separate the wiring from FTP sensor to check which was faulty. I broke the sensor and the stub was still attached to the tank. If this happens to anyone, don't get frustrated. You can use plywood and 5 nails - this may not mean anything but once it happens, you will know. The nails dug into the broken stub, way better than fingers. Stub came out easy. Put a JY sensor in. All went well.

No need to drop the tank. FTP sensor sits between bed-mounting rails. Push down (sufficiently!) and turn 90 degrees to remove it.

Total cost. JY connector $4, JY sensor $2, 1/2" fuel hose to replace deteriorating fuel vapor lines $10, scanner $360..

 

what you mean with JY connector and JY sensor????

 

JY = junkyard.