P1656

P1656 on a Toyota is an Oil Control Valve (OCV) circuit fault on the exhaust-cam side of dual-VVT-i engines — same family of failure as P1349 but on the opposite camshaft. The ECM commands the exhaust OCV through a duty-cycle 0-100% PWM signal to advance or retard the exhaust cam, and watches the exhaust camshaft position sensor for the corresponding 0-50 degree phase response. P1656 specifically calls out an electrical or response fault on the OCV circuit — open, short to ground, short to power, or no mechanical response despite a valid command. Cheapest-first ladder: scan live data and check exhaust OCV duty-cycle commanded vs. actual cam angle (a healthy OCV should sweep smoothly through its full range during a back-probe test with the engine warm). Ohm-out the OCV at its 2-pin connector — most Toyota dual-VVT-i exhaust OCVs read 6.9-7.9 ohms across the solenoid. Check for 12V supply on the OCV power wire with the key on. Pull the OCV and inspect the strainer screen for sludge — same failure mode as the intake-side P1349. If electrical is clean and the screen is clean, the cam phaser itself may be worn (carbon-locked or worn-pin), which is a much more expensive fix involving cam-cover removal. Don't replace the exhaust OCV before checking the intake-side OCV too — on 2GR-FE and 2AR-FE engines, both OCVs share a common oil gallery and feed pressure, so a sludged intake-side strainer can starve the exhaust phaser of pressure and throw P1656 even when the exhaust OCV itself is fine.

Vehicle-specific patterns: 2007-2017 Camry / Avalon 3.5L (2GR-FE) and 2008-2020 Highlander / Sienna / RX350 throw P1656 from rear-bank exhaust OCV failure first because of exhaust manifold heat soak — the rear bank is buried against the firewall and runs 30-50 F hotter than the front bank. 2009-2017 Camry 2.5L (2AR-FE) and RAV4 throws P1656 specifically after extended oil-change intervals because the strainer screen sludges and the exhaust phaser is the first to lose pressure under high RPM load. 2010-2015 Prius Gen3 (2ZR-FXE) Atkinson hybrid throws P1656 during cold EV-to-engine handoffs when oil pressure hasn't fully built — Toyota addressed some cases via ECM reflash. 2008-2014 Lexus IS-F (2UR-GSE 5.0L V8) and 2007-2017 LS460 (1UR-FSE) throws P1656 from a more expensive cam-phaser pin wear pattern that requires cam-cover-off repair. Estimated repair: $200 to $1,800.