So's, i worked at a british car shop as the head mech for 6 years and am now on my own, i have a family friends 04 jag xtype which about a year ago i replaced the throttle body/tpsensor set up due to p1573. The car has now over the last 4 months continued to intermitently have the same code come up along with U1900 can communication bus fault and U2509 torque reduction cant be fullfilled by ems. Just wondering if anyones got any ideas... can this throttle body set up really be going bad again??? ive heard of wiring harnesses having problems because of stretching upon building the cars.... but everything seems to check out ok and the fact that it works fine 80 percent of the time and the other 20 goes into limp mode with all the lights on on the dash.... mind boggling... any help is appreciated! thanks a bunch!
phil email philsk8ts@yahoo.com

 

Phil,

Sounds like it could be a bad electrical connection between the TP sensors and the ECM. The fact that it is OK most of the time may make troubleshooting harder though.

I would suggest you measure and compare the voltage output from each of the TP sensors over the full range of throttle position (engine not running, of course)....i.e., measure voltage from the pink wire (+) to the blue/green wire (-) and compare this to the voltage at the yellow wire (+) to the blue/green wire (-) at the TP sensors.

I suspect the ECM sets a code if the voltage from the two TP sensors differs by more than some threshold. If either TP signal is grossly in error (maybe due to an open circuit or fault), the ECM would also set other codes like P0121, P0122, P0123, P0222, or P0223. If the voltages measured at various throttle positions are the same, none of these codes should appear.

You could also try wiggling, jiggling, pulling and tugging on the wiring between the TB and the ECM while making these voltage measurements.