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OBD II Code: P0021

Copyright AA1Car

Definition: A Camshaft Timing is Over Advanced (Bank 2)

This means the OBD II system has detected a problem in the Variable Vale Timing system that controls camshaft and valve timing. This code is set when the camshaft is out of its commanded position and is advanced compared to where it should be.

Intake and exhaust camshaft timing is typically advanced at mid-range RPM under light load to reduce pumping losses and improve fuel economy.

The "A" cam usually refers to the intake camshaft on Dual Overhead Cam (DOHC) engines, or the intake camshaft for the cylinder head opposite the number one cylinder (bank 2) on a V6 or V8 engine.

The timing position of the camshaft is controlled by a cam phaser that is part of the camshaft drive gear or sprocket. The phaser rotates the cam�s relative position using either a helical gear and hydraulic piston, or a lobed rotor or vaned rotor. The phaser uses oil pressure to change cam timing.

variable valve timing cam phasers .

Possible Symptoms:

Hard starting

Stalling

Rough idle

Poor fuel economy

Possible Causes:

Defective VVT oil flow control valve (stuck open)

VVT oil flow control valve sticking due to oil contamination or varnish buildup

VVT oil flow control valve receiving voltage all the time due to electrical short in wiring

Cam phaser may be stuck in full advance position

Cam phaser return spring (helical gear phasers only) may be broken

Diagnosis:

Use scantool to check status of VVT oil flow control valve. Typically, it should be OFF at idle and ON at higher engine RPM. If control valve is pulse width modulated, duty cycle should change with RPM.

If PCM commands to VVT oil flow control valve are correct, but cam phaser is not changing cam timing correctly or returning cam timing back to base timing after advance command, VVT valve is allowing oil flow to cam phaser all the time, or cam phaser is stuck in full advance position.

Remove oil flow control valve (engine OFF) and test the solenoid by applying voltage. If solenoid valve does not move, the unit is defective and needs to be replaced

VVT oil flow control valve
The location of the oil flow control valve will vary depending on the application,
but is typically on the front timing cover or valve cover.

Repair:

Replace VVT oil flow control valve solenoid. If that does not fix the problem, the cam phaser is likely stuck and needs to be replaced.

Follow the vehicle manufacturer�s disassembly/assembly procedure to replace cam phaser.

Oil and filter change is recommended when replacing either the oil flow control valve or phaser to get rid of dirty oil and to assure a clean oil supply to the control valve and phaser. Dirty oil may cause the oil flow control valve or phaser to stick if varnish or sludge builds up in the oil ports, control valve or phaser.





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