P0164

P0164 means the bank 2 sensor 3 O2 signal voltage is reading above the high threshold (typically over 1.1-1.2V on a narrow-band sensor, or lambda below 0.7 on a wideband), which the ECM interprets as either a stuck-rich condition or an electrical short to a higher-voltage reference. On a post-cat sensor (which is what B2S3 is on most dual-cat-per-bank applications), a stuck-high reading usually means the sensor itself has failed internally with the signal element shorted to its own heater B+, or the harness has chafed against a 12V feed somewhere along the rocker-panel run. Cheapest-first ladder: unplug the sensor and observe the scan-tool reading with key on engine off — a healthy ECM circuit with the sensor disconnected should bias to roughly 0.45V (the internal pull-up reference); if the reading stays pegged above 1.0V with the sensor unplugged, the harness is shorted to a 12V source between the sensor and the ECM; if the reading drops to 0.45V with the sensor unplugged, the sensor is the fault. Verify the heater current is in the normal 0.5-2A range — a shorted heater element internally can bleed B+ into the signal element and produce a high voltage reading. Compare with B2S1 (the upstream sensor) for fuel trim correlation; if STFT/LTFT on bank 2 is within +/-10% (normal) and the post-cat sensor is screaming rich, the sensor is lying. Expensive-misdiagnosis caveat: a coolant leak from a cracked exhaust manifold gasket dumping coolant past the sensor will create a transient high-voltage event that looks identical to a shorted sensor — smoke-test the exhaust before condemning anything.

Vehicle-specific patterns: 2008-2014 GM 5.3L/6.2L Tahoe/Suburban/Yukon with dual post-cat sensors per bank throws P0164 from harness short-to-B+ where the bank 2 sensor 3 wire routes over the starter motor — heat-melted insulation contacts the starter B+ stud. 2007-2010 Ford F-150 5.4L 3V FFV throws P0164 when ethanol-laden fuel cooks the post-cat sensor element internally; the heater bleeds through to the signal wire and produces a stuck-high reading. 2005-2012 Toyota Tundra 4.7L 2UZ-FE throws P0164 from a known internal sensor failure mode where the platinum element delaminates; Toyota covered it under emissions warranty on affected VINs. 2010-2016 RAM 2500/3500 5.7L Hemi throws P0164 from coolant intrusion through the exhaust manifold gasket onto the post-cat sensor wiring. Estimated repair: $150 to $550.