P0064

P0064 is the alternate-definition resistance fault on Bank 2 Sensor 3 — some manufacturers map the resistance-plausibility code to P0064 instead of P0061 depending on which monitoring strategy the ECM is using (input vs. output, low-side vs. high-side resistance check). Diagnostically it's the same flow as P0061: confirm the vehicle has a Bank 2 Sensor 3 via the FSM exhaust schematic, unplug the connector, measure heater element resistance with a DMM at known ambient temperature (2-15 ohms cold acceptable, most OE sensors at 5-9 ohms, drift to 15-50 ohms before OL is what sets the code), back-probe the supply pin and confirm B+ (12.5-14.0V) with key-on, clamp an inductive ammeter for current draw (0.5-2.0A at 12V is healthy) with engine warm. The P0064 code specifically tends to set when the ECM's resistance check is running during a hot-soak condition — meaning the heater element is at peak operating temperature, where thermal expansion in the element shifts resistance out of spec even though the element passes a cold-resistance test. Always measure resistance both at ambient AND after a 20-minute hot-soak before clearing the sensor of suspicion. The expensive misdiagnosis on P0064: techs perform a cold-resistance test, find the heater in spec at 70F, clear the code, and watch it return after the next hot drive cycle — verify hot resistance as part of the diagnostic before pronouncing the sensor good.

Vehicle-specific patterns: 2005-2011 Mercedes-Benz M273 5.5L V8 (S550, CL550, ML550, GL550) is the most common P0064 platform alongside P0061 — Mercedes' ECM firmware splits the resistance fault between two codes depending on whether the check fails on the cold or hot half of the resistance curve. 2003-2010 BMW N62 V8 in 750i/Alpina B7 trim sees P0064 specifically on hot-soak conditions where the rear Bank 2 sensor heat-soaks above 600F and the heater element drifts. 2008-2013 Range Rover 5.0L V8 with the Jaguar AJ-V8 sees P0064 from the same underbody corrosion at the rear sensor connector that triggers P0061. 2009-2014 Audi RS5 4.2 FSI sees P0064 from heater element thermal fatigue on the secondary cat sensor. Estimated repair: $180 to $620.