P0021 on Nissan: How to Diagnose & Fix

The 2017+ Armada uses the VK56VD 5.6L V8 with VVEL (Variable Valve Event and Lift) which is prone to solenoid and actuator failures. The VVEL solenoids can stick or fail, causing rough idle, misfires, and reduced power. This is a common issue shared with the Infiniti QX80. Replacement requires removing the intake manifold.

The VK56 timing chain system uses plastic-faced guides and an oil-pressure-fed hydraulic tensioner. The feed passage to the tensioner is very small and gets restricted by sludge or debris on trucks run on stretched oil-change intervals, so the tensioner loses pressure and the chain goes slack. The chain then saws through the guide face and can contact the chain oiler jet, producing a rattle or squeal from the front cover that is loudest for the first seconds after a cold start and under light load. Left alone, guide material breaks off into the pan, timing drifts, and in the worst cases the chain jumps a tooth.

Both the V42 (2004-2009) and V43 (2011-2017) Quest use the VQ35DE 3.5L V6, and this engine family has a well-documented timing-drive wear pattern discussed at length in Nissan owner communities. Three distinct parts fail: the plastic primary chain guide cracks and breaks up, the secondary (bank) chain tensioners lose their hydraulic bleed-down control, and the primary tensioner plunger sticks. The signature is a loud rattle or buzz for a few seconds on cold start-up as oil pressure builds, plus a rattle on throttle between roughly 1,500 and 2,500 rpm; worn secondary tensioners instead produce a constant whine from the front of the engine. It is a mileage-and-oil-quality failure, most often surfacing past 120,000-150,000 miles and much earlier on engines run on extended or neglected oil changes. Left alone, a disintegrating guide can let the chain jump timing.

P0016 is one of the most well-documented Altima powertrain failures and is a hallmark of the 2.5L QR25DE (it also affects the 3.5L V6). The ECM sets P0016 when the camshaft (Bank 1, Sensor A) and crankshaft signals fall out of their expected relationship. On the Altima this is most often caused by a physically stretched timing chain combined with worn plastic timing-chain guide rails and a failing chain tensioner: as the chain slackens, cam timing drifts and the correlation code sets. The classic early warning is a rattle from the front of the engine on cold start that worsens over time. Related VVT/correlation codes (P0011/P0021/P0024) often accompany it. If ignored, a jumped chain can cause valve-to-piston contact and catastrophic engine damage.

On the 3.5L VQ35DE V6 the plastic secondary timing chain guides/tensioner shoes become brittle and break, and the secondary (cam) chain tensioners lose tension. This produces a loud rattle or whine from the front of the engine, most pronounced for the first few seconds of a cold start. When a guide breaks, the chain runs slack and can contact the tensioner piston (the 'death rattle'), risking valve-timing skip and internal damage if ignored. Owners across multiple Altima forums document this as one of the defining VQ35DE problems, and there is a Nissan TSB covering secondary-chain replacement on 2004-2006 Altimas with the VQ35 engine.