A new common FCA evap fault
The code P0441 has caused some confusion on newer FCA trucks. P0441 is an SAE code for incorrect purge flow. After correctly repairing several newer FCA vehicles with the P0441 code incorrectly diagnosed by others this updated evap system is worthy of a discussion.
This particular vehicle is a 2016 Patriot. diag.net/file/f7f82r8sr… but this issue is common in many newer FCA vehicles.
The code indicates incorrect purge flow. In the past purge flow was monitored by the engine module with the following procedure commanding open the purge control valve and looking at the state of the ESIM switch to see if it closed and also monitoring idle speed and O2 voltage to indicate the system allowed evap vapors to enter the engine while the engine is running when the purge valve was commanded open
Depending on the model most FCA vehicles now include a fuel tank pressure sensor located in the evap line near the fuel filler tubes
The term fuel tank pressure sensor is misleading. While it does measure evap pressure that is not its primary function. The only input the tank pressure sensor is responsible for is to verify the evap system pressure changed when the purge valve was commanded open. The sensor will report a change in pressure when the evap purge valve is commanded open to verify the purge flow reached the fuel tank system while the engine is running. The controller still monitors O2 sensors and idle speed to verify purge flow but has added the pressure sensor so that also during the koeo portion of the small leak test the purge can be opened and at which point the pressure would change in the previously sealed system. The pressure change reported when the purge valve is commanded open proves that the sealed system now has a leak when the purge was opened indicating that the purge valve and lines are all intact to the tank system.
Once it is understood that the only function of the pressure sensor is to verify purge flow and NOT for leak detection the system is then fairly straightforward to diagnose.
The system is checked for leaks and ESIM switch function the same as the older systems that include the use of the ESIM.
Begin by attaching the smoke machine to the fresh air tube on the ESIM assembly. Apply the smoke and monitor the flow indicator for any signs of leakage. Once pressure is applied the ESIM switch will need to change from open to closed.
Monitor the flow of the smoke machine all flow should stop indicating a sealed EVAP system.
Next step would be to command the purge solenoid open with the scanner koeo and monitor the flow indicator
it should show flow now verifying the leak created by the open purge valve.
Also the ESIM switch should now switch to open.
Monitor the fuel tank pressure sensor before turning on the smoke machine.
it should indicate close to atmospheric pressure. This one indicates a very large amount of vacuum that is not possibly accurate. Concerned that maybe there is an issue with the scan tool data or wiring for the pressure sensor the actual tank pressure sensor voltage is measured
and compared to the scan tool reported voltage
the actual voltage at the sensor matches the scan tool data so the displayed voltage and pressure on the scan tool can be trusted as accurate.
With the voltage at the sensor verified and is in correlation with scan tool data it is accurate to pronounce the sensor failed as it is not possible for the vacuum to be that low in the EVAP system
so no doubt this fuel tank pressure sensor is failed.
The following test procedure is the quick method I use when diagnosing the P0441 code it is quick and easy.
Of the sensors failed all of them report a very low vacuum in the system. It is now a quick diagnosis as the sensor pressure reading is monitored koeo
the fuel cap is removed to verify atmospheric pressure is present in the EVAP system. If the sensor is still reporting an abnormal amount of vacuum the last step in the quick diagnosis is to compare actual sensor voltage
to scan tool reported voltage
if they are the same then it is safe to call the sensor failed.
After diagnosing several of these fuel tank pressure sensor failures the last test that was described here is quick and easy usually consuming less than 20 minutes.
The key take away is that the fuel tank pressure sensor is not used for system leak detection rather it is only used to verify the whole purge system is intact and functioning correctly.
Nice write-up Robert! Thanks for the info. Just when you think you know FCA's newest EVAP system they go and add another component that of course is now a common failure !
Excellent write up, Great Job Robert! I remember visiting your shop some 20 years ago with our Moog, Everco, Wagner Tech Van.
Thank you Robert, excellent presentation!
Great content! Thank you!
Awesome right up! We ran into this a few weeks ago, another shop had tried to tackle the issue and could not find the problem. Fuel tank pressure sensor pins were all corroded causing faulty reading.
Excellent write-up Robert, with great photographic support. While I'll never touch one of these vehicles in my work, this information may be invaluable to others who may encounter this concern!
Thanks Robert nice write up, really enjoyed , valuable information , thanks for sharing it
You have presented this perfectly! 1. Here is "a system" and how it works. 2. Here is what usually breaks. 3. Here's how you check it. That is the Trifecta of perfect instruction, sir!