P2237

P2237 sets on a wideband (AFR / air-fuel-ratio) upstream O2 sensor on bank 1 when the ECU detects an open or implausibly low pumping-current control circuit — the wideband sensor needs the ECU to actively drive a small pumping current (typically ±2 mA across the lambda 1.0 stoichiometric point) through the sensor's pumping cell to maintain a fixed oxygen concentration at the Nernst reference, and the actual lambda is read off how much current it takes. When the pumping-current driver circuit is open or the wiring to it is broken, the ECU can't control the sensor and sets P2237. Cheapest-first ladder: inspect the connector at the sensor for corrosion and pushed pins — the wideband connector typically has 5-6 wires (heater B+, heater ground, pump cell, Nernst cell, virtual-ground reference, sometimes calibration resistor) and a single corroded pin kills the pumping circuit. Backprobe the pump-cell wire with the engine warm and look for the ~3V virtual-ground sitting steady; if it's pinned to 0V or 5V, the circuit is open or shorted. DMM the heater pins (2-4 ohms cold on most wideband sensors) — a sensor with a failed heater never reaches the 700°C+ element temp it needs to pump current. Wideband sensors are far more expensive than narrow-bands ($150-$350 OEM) so verify the harness side before parts-cannoning.

Vehicle-specific patterns: 2005-2012 Toyota 2GR-FE 3.5L V6 (Camry, Avalon, Sienna, Highlander) throws P2237 routinely past 120k miles — Denso wideband sensors degrade and the pumping circuit eventually opens internally; replace with OEM Denso, aftermarket Bosch widebands often throw new codes on this platform. 2006-2014 Subaru EJ25 (Forester, Outback, Legacy) throws P2237 from a chafed front O2 harness where it routes past the exhaust crossover, plus genuine sensor failure around 100k miles; the front sensor is the wideband and the rear narrow-band lasts much longer. 2008-2013 BMW N55 turbo I6 (335i, 535i, X3, X5) throws P2237 from a connector heat-damage issue near the turbo and from wideband element failure around 80k-110k miles. 2007-2014 Mazda 2.3L DISI turbo (Mazdaspeed 3/6, CX-7) throws P2237 from oil-fouled wideband elements when the turbo seals leak past the compressor. Estimated repair: $200 to $550.