P0021 Code: "A" Camshaft Timing Over-Advanced or Performance (Bank 2)
The bank 2 intake cam is more advanced than commanded or slow to respond; compare it with bank 1 first.
At a glance
Severity: Moderate
- Meaning
- "A" Camshaft Timing Over-Advanced or Performance (Bank 2)
- System
- Fuel & Air Metering · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $50–$3,500
- DIY difficulty
- Moderate
P0021 applies to V and boxer engines and means the bank 2 intake cam is either sitting further advanced than the PCM commands or taking too long to reach its target. Each bank has its own oil control valve and phaser but shares the oil supply, the oil pump and usually the primary chain with the other bank. That makes bank 1 your best test instrument. If P0011 set at the same time and both banks misbehave alike, suspect something shared, such as low or wrong oil. If bank 1 tracks its target perfectly while bank 2 lags or overshoots, the cause lives on bank 2 alone: its control valve, the oil screen or passage feeding it, its phaser, or its chain and tensioner. Idle quality often suffers because one bank is now running a different valve overlap from the other.
Can I keep driving? Drivable with care; expect a rough or uneven idle and possible stalling as you stop. If the oil is low, top it up before driving, and don't leave the code for months, because an oil supply problem that upsets the phaser also starves the chain tensioner.
How to read P0021
- P Powertrain
- 0 Generic (SAE)
- 0 Fuel/air & emissions (aux.)
- 21 Specific fault
Symptoms
- Uneven idle that feels as if one side of the engine is working differently
- Stalling or a dipping idle when you come to a stop
- Sluggish response at low speed
- P0021 alone, or together with P0011 when an oil problem affects both banks
- Code appearing soon after an oil change with the wrong grade
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Bank 2 oil control valve sticking or leaking internally
- Oil low, old or the wrong viscosity (P0011 usually appears as well)
- Clogged filter screen or restricted passage feeding the bank 2 valve
- Bank 2 intake phaser worn or binding
- Bank 2 chain, guide or tensioner wear shifting the cam
- Intermittent solenoid connector or wiring causing erratic control
Diagnosis step by step
Check the oil and note which banks are affected
Read the dipstick and check the service history for the grade that went in. If P0011 is stored too, correct the oil before anything else and see whether both codes stay away.
Tools: Flashlight, OBD-II scanner
Compare both banks in live data
Record desired and actual intake cam angle for bank 1 and bank 2 at idle and at 2,000 rpm. Bank 1 following its target while bank 2 overshoots or lags isolates the fault to bank 2 hardware.
Tools: OBD-II scanner
Swap the bank 1 and bank 2 intake valves
On most V engines the two intake control valves are interchangeable. Swap them, clear the codes and drive; if the fault reappears as P0011 on bank 1, the valve is the culprit.
Tools: Screwdriver, OBD-II scanner
Inspect the bank 2 oil feed screen
Some engines, including several boxers, have a filter screen in the oil passage to each bank's control valve or phaser. Remove it and look for debris; clean or replace it, then work out where the debris came from so it doesn't happen again.
Tools: Flashlight, Torque wrench
Check phaser response and noise
Command the bank 2 intake cam through its range and watch how smoothly actual follows desired. A phaser that jumps, hangs or rattles on startup is worn even when fresh oil and a good valve are fitted.
Tools: OBD-II scanner
Look at the bank 2 chain drive if it persists
If the code survives oil, valve and screen checks, look at the bank 2 cam/crank correlation values. Drift toward the limit, or a P0018 in history, sends you to the chain, guides and tensioner on that bank.
Tools: OBD-II scanner
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Oil and filter change with the specified viscosity | Yes | $50–$120 |
| Replace bank 2 intake oil control valve | Yes | $120–$380 |
| Clean or replace bank 2 oil feed screen | No | $100–$350 |
| Replace bank 2 intake cam phaser | No | $700–$1,600 |
| Bank 2 or complete timing chain service | No | $1,200–$3,500 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Subaru
Turbocharged Subaru EJ engines with AVCS, such as the WRX STI, Legacy GT and Forester XT, have small oil filter screens feeding the AVCS system on each head. When they clog, P0011 or P0021 follow; on a Subaru boxer, bank 2 is the left-hand bank with cylinders 2 and 4. Cleaning or replacing the screens is a known and moderately priced fix.
Nissan
On Nissan VQ V6 engines the intake valve timing control solenoids sit on the front of each cylinder head and are the same part left and right, so swapping them is an easy first test for P0011 and P0021. Low oil level and stretched oil change intervals are frequent triggers on these engines.
Field data
| Subaru | 6 | ||
|---|---|---|---|
| Ford | 4 | Expedition, Expedition El, F-150 SUPERCAB | |
| Chevrolet | 3 | Traverse | |
| Hyundai | 3 | Santa Fe |
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
P0021 turns on the check engine light, which is an automatic fail at an OBD-II emissions test. If an oil change fixes it, clear the code and allow several days of driving so the monitors complete before you go.
Frequently asked questions
I have P0011 and P0021 together. Are both solenoids bad?
Unlikely. Two banks failing at once usually share a cause: low oil, overdue or wrong-grade oil, or a weak oil pump. Fix the oil first; only if one bank keeps logging codes afterward is its solenoid a real suspect.
Why is the idle rough when only one bank has a code?
Because the two banks now run different valve overlap. The bank with the advanced intake cam pulls exhaust back in at idle and makes less power than the other, so the crankshaft gets uneven pushes.
Can I swap the bank 1 and bank 2 solenoids myself?
On many V6 engines, yes: each one is held by a bolt and has a single connector. Clean around them first so no dirt falls into the oil passages, and use new O-rings if they look flattened.
Could the timing chain cause P0021?
It's possible if the code comes back after the oil and valve have been ruled out, especially with a rattle or a P0018 in memory. Check the correlation values before buying phasers, because a worn chain would make new phasers read wrong too.
Sources
- SAE J2012 – Diagnostic Trouble Code Definitions
- ISO 15031-6 – Road vehicles, diagnostic trouble code definitions (EOBD)
- Manufacturer public service information (cross-checked)
- NHTSA Complaints API
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy