I have a 04 f150 and it is throwing a P0451 code. It is suppose to be the tank pressure sensor. I started Torque pro and tried reading the pressure on the pid. On the manage custom pid page it says it is pid:221639 and the max/min is suppose to be 10.0/0.0. When I read it, the pid says the pressure is 4507PSI! The Equation shown is :((A*256)+B)*0.1449 . Is the Equation wrong or why is it reading sooooo far off. I have 2 Bluetooth adapters I have tried. 1 does not read this pid at all, and the other that has the Torque drawing and name on it that reads the wrong number. Any help will be appreciated. Do I need a different adapter (suggestions)? I hope someone will chime in before I have to drop the tank and purchase a sensor that might not be the problem. When I pull the cap off the tank when it is cold and pressurized by the ecu, the pid did change but I did not catch the number changes at the time. Thanks in advance for any help or suggestions.
Don

@Capp777

The information you gave the OP is CORRECT — _BUT FORD MOVED THE PID_ on you -Darn them!. The Formula in the Torque Pro extended PIDs are not correct (((( FOR THE 2004 FORD F150 Lariat – at least)))). I have well learned that PIDs are NOT STANDARDIZED, even across different models of like brands, let alone universal.

I have gone crazy trying to sort out FTP on my 2004 Ford Truck. This is what I have learned. It seems that FORD ‘changed’ PID # 1639 from an OBDII ‘output’ reading FTP in Pascals as derived from the Fuel Tank pressure sensor voltage (which may NOT have previously been represented on OBDII at all — IDK). NOW PID 1639 is true Fuel Tank Pressure volts – unsigned 0 to 65535, I think in A/D counts, in some binary increment, perhaps 4 counts each A/D unit. ???

But, PID #1639 NOW shows Fuel Tank Pressure volts. The following formula produces an accurate reading as can be checked with a VOM on PIN ’44’ (20ga, Rd/Pk wire) at the 70 Pin Power Train Control Module plug.

PID # 1639

221639, Fuel Tank Pressure volts, FTPv, (A*256+B)/13107

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The previous FTP ‘Output’ in Pascals was moved to PID # 1687. Apparently from the fuel tank pressure volts input – the PCM calculates fuel tank pressure into (the fine resolution) of Pascals. It can be positive OR negative because either “+” pressure builds up in the tank from the fuel vapors (if sealed and the carbon canister is somewhat clogged), or negative when the EVAP purge valve is modulated open to build manifold vacuum in the tank for EVAP tests. Normal readings are from ~ +50 to +100 Pa down to ~ negative 8000 – 9000 /// (perhaps 10,000 Pa if air cannot be draw air into the tank during EVAP tests through the normally open Evaporative canister vent valve.

The calculated pressure in Pascals is output DIRECTLY on PID 1687.

221687, Fuel Tank Pressure in Pascals, FTP_Pa, Signed(A)*256+B

A more common scale (TO ME) is Inches of Water. So the following formula converts the OBDII Pascals output into inches of water. I set up two gauges to display FTP in BOTH values as follows.

221687, Fuel Tank Pressure InH2O, FTP_InH2O, (Signed(A)*256+B)*0.0040146307866177

NOTE: (DISCLAIMER). AS FAR AS I KNOW, THIS INFORMATION IS APPLICABLE TO ONLY 2004 FORD F150 (gas) – probably through 2008 FORD for sure. Outside of that, I have NO IDEA.

Happy Torqueing

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Your FTP ‘voltage’ readings do not look too out of whack – according to the “Daignostic Reference Values Values” http://www.devoll.com/public/5-4L_3v_F150_diagnostics_reference_values.pdf

The PCM Plug layouts are shown on top. BUT Beware – it doesn’t indicate it but the drawing is ‘stupidy’ as viewed from inside the CAB, not from under the hood. Also, I question the PCM Pin (B65), as that is not what I determine from the Schematics!! http://www.devoll.com/public/f150-wiring-Engine-Performance-wiring-pgs1-to-6-of-6.pdf Appears to me to be on 58, (or 44 with ref voltage on 29).

Two other points. You may need to increase number of decimal places on your voltage gauge to 3 to get a better idea of what’s happening, and Inches of Water are ‘little bitty’ compared to Kpa.

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@Amtp1, I have set up a temporary private email account for you on my mail server. F-150Torqued-Amtp1@devoll.com

If you will send your email address to me there, I will provide you some more good documentation that I have for our trucks.

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