P0061

P0061 means the heater circuit resistance on Bank 2 Sensor 3 is out of the plausibility window — same diagnostic logic as P0060 but on the third sensor of Bank 2, which only exists on multi-cat exhaust systems (typically European V8s with a pre-cat + mid-cat + post-cat sensor layout, or certain Asian V6/V8s with a four-O2 monitoring scheme). Cheapest-first ladder: confirm via FSM exhaust schematic that the vehicle actually has a Bank 2 Sensor 3 before parts-cannoning — verify the sensor location physically and identify the connector before tooling on the wrong one. Unplug Bank 2 Sensor 3 and measure heater element resistance with a DMM at known ambient temperature; a healthy heater reads 2-15 ohms cold (most OE sensors at 5-9 ohms), and an aged heater drifting toward open reads 15-50 ohms before going OL — that drift is what sets the resistance-plausibility code. Backprobe the supply pin with the connector reconnected and engine running warm; confirm 0.5-2.0A current draw at 12V. Check the connector pins for corrosion (which raises measured resistance without an actual element fault). The expensive misdiagnosis on P0061: shops replace what the scan tool labels Sensor 3 only to find the new OEM sensor still throws P0061 because the resistance fault was actually in the connector pins, not the element — clean the pins with electrical-contact cleaner and a pin-burnishing tool BEFORE condemning the sensor.

Vehicle-specific patterns: 2005-2011 Mercedes-Benz M273 5.5L V8 (E550, S550, CL550, ML550, GL550) is the most common P0061 platform — the Bank 2 multi-cat layout has three sensors per bank in export-market configurations, and the rear sensor (labeled Sensor 3) sees the most heat-soak fatigue. 2003-2010 BMW N62 V8 in certain trim levels (especially long-wheelbase 7 Series and Alpina variants) ships four O2 sensors total and what BMW firmware calls Bank 2 Sensor 3 is the rear-bank mid-position sensor — the harness routes through the transmission tunnel and the connector pins corrode at the seam. 2008-2013 Range Rover 5.0L V8 (Jaguar AJ-V8) sees P0061 from chronic underbody harness exposure on the Bank 2 rear connector. 2009-2014 Audi 4.2L FSI V8 (RS5, S5 4.2) in certain markets carries a Sensor 3 designation on the secondary cat. Estimated repair: $180 to $620.