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Discussion Starter #21
Got it back from the dealer yesterday. 2 hours of labor for doing some diagnostic and the fault is cleared. Here is the wright up from the dealer

STATES POOR EXHAUST MESSAGE KEEPS COMING ON
P204C- RELUCTANT PRESSURE SENSOR CIRCUIT LOW VOLTAGE. THIS DTC IS IN A PASSED FAILED STATUS, THIS CODE IS NOT RELATED TO THE POOR QUALITY EXHAUST FLUID MESSAGE. THE TECHNICIAN CLEARED DTC, PERFORM A PRESSURE TEST AND THE SYSTEM PASSED. THE TECHNICIAN PERFORMED A EXHAUST FLUID QUALITY TEST, TEST PASSED AND THE MESSAGE WAS NO LONGER PRESENT. THE TECHNICIAN TEST DROVE THE VEHICLE, NO DTC'S RETURNED AND THE POOR EXHAUST FLUID MESSAGE IS NO LONGER PRESENT.

the P204C fault came up when I was checking the wiring going to the DEF tank heater module. I unplugged one of the wires when the car was running and it shut down and that code came up. I plugged it back in and after a few restarts the CEL went out. I did not clear the code because I was using the counter for "Miles driven from last reset" to keep up with how far I'd driven since last time Id cleared all the codes from swapping the DEF tank heater module. Only thing they could really say is that swapping the heater module must have fixed the issue but for some reason the fault did not clear until they did there testing. Spending $275 at the dealer for 2 hours of labor its a little upsetting but is a lot better that then 2k-3k I was expecting.
 

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Based on those readings, either NOX2 or something involved with getting the DEF into the system (lines, injector, etc.) are the problem. NOX1 should vary with engine load/speed/temp. NOX2 should be steady, but 99 seems high. (Unfortunately, I'm no longer able to give a reference value from my own vehicle on what a proper NOX2 reading should be.) If I can remember correctly when I did look at those values long ago, it seems like NOX2 should be at or near zero if the SCR is working properly. Will be interesting to see what the dealer comes back with and if they're successful.
See attached from my car biscan/torque.

This car has no issues and 35k.
285041
 
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