After replacing the fuel pump (what a nightmare) in my brother's 2003 XJ8, the car now has the CEL with a P0453 code.

I did a Google search and found this post:
https://www.jaguarforums.com/forum/x...91/#post694927

I don't understand a few things about the post but I'm going to go back in the trunk and check for a loose ground that I may have failed to install.

I did destroy the fuel pressure line which I did replace and roughed up the fuel return line which is not leaking. I was thinking that it was a vacuum leak because one of the vacuum lines on top of the tank split when I removed it, so I trimmed it and put it back on.

Here is the info in the linked post (not sure how to access the FTP sensor with the OBD2 tool):
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Evaporative Emission System Pressure Sensor/Switch High
What does this mean?
OBD Code P0453refers to
The EVAP (Evaporative Emissions) System allows fuel tank vapors to be purged into the engine and burnt rather than expelled into the atmosphere as harmful emissions. The EVAP system contains a pressure sensor to check the integrity of the system. Periodically, the EVAP system performs a pressure test to check that there are no leaks in the system. It uses this sensor, also known as a fuel tank pressure (FTP) sensor to check for leaks. Basically P0453 means the PCM (Powertrain Control Module) noticed the EVAP Pressure sensor or FTP is indicating a higher than normal pressure (above 4.5 Volts) in the EVAP system. NOTE: On some vehicles the FTP is a part of the fuel pump assembly in the tank.

Symptoms
Possible sumptoms of OBD code P0453
There will likely be no noticeable symptoms along with this code other than the MIL (Malfunction Indicator Lamp), commonly known as Check Engine Light illumination. However, there may be noticeable fuel odors in some cases.

Causes
Possible causes of OBD code P0453
A P0453 DTC trouble code may be caused by one or more of the following: Open on FTP sensor signal wire Short to voltage on FTP sensor signal wire Bad FTP sensor Abnormally high pressure in fuel tank due to blockage in EVAP purge hoses or overfilled tank Loose/damaged FTP sensor connector Loss of ground to the sensor

Possible Solutions
Using an scan tool access FTP sensor value with Key on Engine off (KOEO). Normal value is usually somewhere near 2.5 Volts at atmospheric pressure (may fluctuate some due to altitude). It shouldn't ever be above 4.5 Volts. 1) If it is close to 2.7V with the gas cap off, the problem is likely intermittent. Using a Digital Volt Ohm Meter, measure the voltage on the signal wire while trying to induce the problem by wiggle testing all the wiring at the FTP sensor. If the voltage fluctuates when wiggle testing, check for connector problems; i.e. water in the connector, broken or chafed wiring. 2) If the value shown on the scan tool is above 4.5V, unplug the sensor (if possible) and check for voltage again. If the high voltage is still present when unplugged, inspect wiring harness for a short to voltage on the signal wire. If the high voltage disappears when unplugging the sensor, check for a good ground to the sensor and proper reference voltage. If you have a good ground and 5 Volts reference voltage, replace the FTP sensor since it's likely shorted out.
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Well, first off, how is the car running? ...rough, smooth, stutters on acceleration? Did you do just a P0453 search or did you put Jaguar in front of the code? I highly recommend putting Jaguar (or whatever vehicle make) in front of any code search to get more specific results per the manufacturer. In your case I returned this... P0453 Jaguar Auto Trouble Code With All Car Models | Auto Trouble Codes - AutoTroubleCode.com

 

Jaguar's own codes data (free download on here and I expect on JagRepair.com - Jaguar Repair Information Resource) also lists the known causes.

 

Yes I put Jaguar XJ8 2003 in the Google search. The results link you provided was really vast, from a transmission issue, to egr error, to vacuum leak to low fuel pressure. Really out there.

 

The issues it covers mostly are generic simple standard inexpensive checks (you haven't told us your symptoms to be more direct) ...that if any is your problem, I'd think you'd be happy to fix vs the injectors or timely and possible expensive transmission.
But, what are the cars symptoms to help us to try to be more specific?