Error Code P0021 is defined as A Camshaft Timing Overbalanced, Bank 2. Generally, this refers to over advanced timing or system performance trouble on Bank 2. For Nissan vehicles, this means a problem on camshaft variable timing control – Bank 2 – performance. This code is the same with P0011, except that the problem is in the Bank 2, not in Bank 1.
Error Code P0021 means that the OBD II system has found a problem in the PCM’s (Powertrain Control Module) Variable Valve Timing (VVT) or Variable Camshaft Timing (VCT). This code shows up when the camshaft is not in the position commanded, and advanced of where it’s supposed to be.
To improve fuel efficiency and reduce pumping losses, both exhaust camshaft timing and intake are usually advanced at mid-range RPM with light load.
The ‘A’ cam typically refers to the intake camshaft on DOHC (dual overhead cam) engines or the intake camshaft for cylinder positioned head opposite to the number 1 cylinder (bank 2) on V6 and V8 engines.
The timing of the camshaft is controlled by the cam phaser, which is a component of the camshaft drive gear (or sprocket). It uses oil pressure to change timing and rotates the cam’s relative position through either hydraulic pistons, helical gear, vaned or a lobed rotor.
Aside from the illumination of the Check Engine Light, the most common symptom of this code is the engine idles normally, but stalls or hesitates upon acceleration. Other symptoms include:
- Reduced fuel efficiency caused by the camshaft not being in the right position
- Engine emissions exceed federal levels
- Hard starting, stalling, rough idle
- More advanced camshaft than the PCM has commanded
- Advanced camshaft when it’s supposed to be retarded to lower timing level
- The OCV (oil control valve) connected to the Bank 2 may be stuck open or clogged
- Oil too thick, which results to clogging to the passage. A problem caused by a lack of or incorrectly performed oil changes.
- Camshaft phaser stuck in full advanced position
- Cam phaser return spring is broken (exclusive for helical gear phasers)
How to Check
Mechanics usually start with visual inspection of the connectors and wiring. Then, he will check the engine for signs of sludge and make sure the engine oil is the right viscosity. Experienced car/vehicle owners and DIYers can actually do these steps as well.
A scan tool should be used to check the VVT oil flow control valve status. Usually, it must be On at higher RPM and Off at idle. Its duty cycle should also change with the RPM if the control valve is pulse width modulated.
If the PCM says there’s no problem on VVT oil flow control valve, but the cam phaser doesn’t change timing properly or returns cam timing to the base timing after an advanced command, that means the VVT valve continuously allows oil flow in the cam phaser, or the cam phaser may be stuck in the advanced position.
Test the solenoid voltage. Make sure you turn off the engine before removing the oil flow control valve. If the solenoid doesn’t move, that means the unit needs replacement as it’s already damaged.
How to Fix
Repairing this error code is pretty straightforward. You can replace the VVT oil flow control valve solenoid. If that doesn’t seem to solve the problem, and that the cam phaser must have been stuck open, then you need to replace the cam phaser.
It is also highly recommended to change the oil as well as the filter when replacing either the cam phaser or oil flow control valve. This is to remove dirt residue and dirty oil and make sure the control valve and phaser gets a clean oil supply. Dirty oil can build up in oil ports and compromise the performance.
Make sure you read carefully, understand and follow the manufacturer’s assembly/disassembly instructions on replacing cam phaser.
Dealer techs usually have the advanced tools, knowledge and skills to follow detailed troubleshooting instructions from the manufacturer, and the access to advanced scan tool, so you might want to get their help.