CELICA (1.8L 2ZZ-GE)

Variable Valve Lift (VVL) system controls amount of intake and exhaust valve lift while engine is operating at high speeds to provide improved engine performance and fuel economy. VVL system consists of camshaft timing Oil Control Valve (OCV), camshaft changeover mechanism, camshaft position sensor, crankshaft position sensor, engine coolant temperature sensor, camshafts with low-and-medium-speed camshaft lobes and high-speed camshaft lobes, Engine Control Module (ECM) and associated wiring. See Fig 1.

When engine is operating in low-to-medium-speed range, low-and-medium-speed camshaft lobes operate to move the valves by using needle roller and rocker arm on camshaft changeover mechanism. See Fig 1. The high-speed camshaft lobes also push downward on the rocker arm pad, but because rocker arm pad moves freely, this movement of high-speed camshaft lobes does not cause the rocker arm to move the valves. When engine coolant temperature is greater than 140°F (60°C) with engine speed greater than 6000 RPM, the ECM operates oil control valve for VVL system to allow oil pressure to be applied to the rocker arm pin. See Fig 1. When oil pressure is applied to rocker arm pin, rocker arm pin is pushed to the locked position. This prevents rocker arm pad from moving freely, this changes operation from low-and-medium-speed camshaft lobes to the high-speed camshaft lobes. This provides more valve lift for improved engine performance and fuel economy.

Oil control valve for VVT is an electrically controlled valve that receives oil pressure from the oil pump. See Fig 2. When engine is operating in low-to-medium-speed range, ECM operates oil control valve to move spool valve to open position. This allows oil pressure to drain instead of being applied to rocker arm pin for use of high-speed camshaft lobes. When engine coolant temperature is greater than 140°F (60°C) with engine speed greater than 6000 RPM, ECM operates oil control valve to move spool valve to the closed position. This allows oil pressure to be applied to rocker arm pin for use of the high-speed camshaft lobes. The ECM uses input signals for engine speed, intake air volume, throttle position and engine coolant temperature to determine operation of oil control valve for VVT. If a problem exists in the VVL system, a Diagnostic Trouble Code (DTC) may be stored in ECM. See TESTING PROCEDURE under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article for retrieving of DTCs.

Fig 1: Locating Variable Valve Lift System Components (Celica 1.8L 2ZZ-GE)

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