P0021 on Toyota: How to Diagnose & Fix

The 3.5L 2GR-FE V6 commonly develops oil leaks from the VVT-i oil line, timing cover, and valve cover gaskets. The VVT-i oil hose fitting loosens over time, dripping oil onto the exhaust manifold creating a burning smell and fire risk.

The 1998-1999 100-series (UZJ100) switched to the 4.7L 2UZ-FE V8, which uses a rubber timing belt on a ~90,000-mile replacement interval. The timing-belt-driven water pump, the hydraulic tensioner, and the idler pulleys are the common failure points and are typically leaking or worn by that interval (water-pump failure often precedes belt wear). There is a long-running interference vs. non-interference debate: Toyota officially lists it as interference, but the community consensus (and documented belt breaks on the early non-VVT-i 2UZ-FE) is that it generally does not bend valves when a belt snaps at low RPM. Regardless, a broken belt strands the vehicle, and careless belt jobs can nick the crank sensor reluctor wheel or pinch/route wiring wrong, causing no-start or timing DTCs.

On the 3rd-gen Tacoma's 3.5L 2GR-FKS (2016+), P0016 means the ECM sees the Bank 1 intake camshaft position out of correlation with the crankshaft. Unlike the OCV-driven P0011, P0016 more often reflects a mechanical timing error — a slightly stretched timing chain or a worn/sticking VVT-iW cam timing gear (actuator) in the cam hub — or the system's well-known sensitivity to oil condition. The 2GR-FKS VVT-iW (wide-authority) system uses high oil pressure through cam-hub actuators, so low, aged, or wrong-viscosity oil, or a clogged oil-control-valve filter screen, can starve the actuator and throw a correlation code. It commonly appears alongside cold-start rattle and sometimes P0011/P0012/P0021/P0022.

Tundras with Toyota's VVT-i system can produce a brief (~1 second) rattle or knock at cold start. The cause is the intake-side VVT 'cam gear' (variable cam timing actuator): when oil drains back out of the VVT unit overnight, the lock pin is disengaged and the internal components impact the housing during initial cranking before oil pressure refills the unit. Toyota addressed the condition with TSBs and revised cam-gear/actuator designs on affected engines. While brief rattle is usually benign, severe cases can let the VVT housing and sprocket separate, causing the engine to stop.