'97 E320: Diagnostic Code P0170 (generic) Question

Today, on a local errand, while inching ahead in a parking lot there was a discrete beep from the dash and the "Check Engine Light" and "check
engine electronics" messages came on.
The 104.995 24 valve straight six starts and runs flawlessly; it's done 37,820 miles.
I checked the generic code; it's P0170 which the booklet tells me is a "Fuel Trim Malfunction."
What's that in plain English?
Fuel system pressure?
If so where's the fuel pressure sensor?
930 miles ago the shop replaced #6 fuel injector - any implication between that and "fuel trim malfunction"?
Thanks for your thoughts and opinions.
Tom
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Tom,
This is what I found on P0170:
===P0170 AND P0173 FUEL TRIM MALFUNCTION
Diagnostic trouble code (DTC) P0170, bank #1, and DTC P0173 bank #2, indicate the fuel/air ratio is too rich or lean.
Possible causes:
Fuel System: Excessive fuel pressure, Leaking fuel injector(s), Leaking fuel pressure regulator, Low fuel pressure, Plugged injector(s), Damaged/disconnected HO2S circuit.
Induction System: Air leaks after the MC-VAF/MAF, Vacuum leaks, Restricted air inlet, PCV system.
Base Engine: Oil overfill, Cam timing, Compression,
Ignition: Coil and secondary side of ignition system. Check air intake for leaks, obstruction, and damage. Check air filter, air filter housing for blockage. Check PCV system integrity. Check engine vacuum integrity
==== So it *could* be a leaky injector.
HTH,
Josh

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Thanks, Josh, for the comprehensive menu of possibilities. As an injector was replaced only 900 miles ago I'll focus on the elements that may be or have become loose, especially in the air induction system and report the findings.
The engine runs perfectly so it's a small leak, or whatever.
Tom
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Good luck. BTW, I'm amazed at two things: (a) You have a '97 E320 with just 37K miles and (b) it already needed an injector.

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Needed the injector after 4 years and 15K miles - but I didn't know it to claim under the warranty.
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I checked the fuel pressure regulator, the air filter, the ducting between the MAF and the engine's air intake, looked for a loose or disconnected vacuum line and checked the fluid levels. Nothing found.
Engine runs fine so I'm tempted to erase the P0170 code and see what happens next.
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