P0173 - Fuel Trim Malfunction (Bank 2)
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P0173 indicates that the Engine Control Unit (ECU) has reached its calibrated limit for fuel trim adjustment on Bank 2. When the Long Term Fuel Trim (LTFT) exceeds its correction threshold (typically +/- 20-25%), the ECU can no longer maintain a stoichiometric air-fuel ratio. Unlike P0171/P0174 which specify lean conditions, P0173 is a general malfunction indicating the system is unable to stabilize the mixture, often caused by sensor bias or unmetered air/fuel delivery issues.
Possible Causes
Vacuum leak specifically affecting Bank 2 intake
Faulty or contaminated Mass Air Flow (MAF) sensor
Faulty Oxygen Sensor (O2) on Bank 2 (sensor bias)
Defective fuel pressure regulator or leaking fuel injectors on Bank 2
Symptoms
Recommended Solution
Workflow
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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