P0021: Bank 2 'A' camshaft (usually intake) timing is more advanced than commanded, or the system is not performing
'A' camshaft position - timing over-advanced or system performance (bank 2)
Severity: Inspect soon
P0021 means the bank 2 intake cam is not following the timing the engine computer commands. The engine usually keeps running, sometimes roughly; it is an emissions-monitored VVT fault and can come from low oil or a stuck solenoid, so get it inspected soon.
It gets more serious if:
- Stop: The check engine light starts flashing. That means misfire heavy enough to overheat and damage the catalytic converter; avoid further driving and get it checked.
- Stop: A new loud rattle or knock from the timing area, or the engine stalls or will not restart. A worn chain, guide or tensioner can be behind this code and further driving risks engine damage.
P0021 in short
P0021 means the bank 2 intake camshaft is more advanced than the engine computer wants, or is slow to reach its target. Check the oil level and grade first, then the bank 2 oil control solenoid; some Subarus need a software update. Get it inspected soon; stop if the engine rattles or knocks.
Variable valve timing uses oil pressure, steered by an oil control solenoid, to rotate the camshaft relative to its sprocket. The engine computer commands a cam angle and checks that the cam reaches it. P0021 sets when the bank 2 'A' camshaft (the intake cam on most engines) stays ahead of the commanded angle or responds too slowly.
Bank 2 is the side of a V or flat engine without cylinder 1. Because both banks share the same oil, P0011 (bank 1) together with P0021 points at oil supply or calibration rather than one bank's parts.
Subaru has issued engine computer reprogramming for rare P0011/P0021 on 2023 models and a diagnostic bulletin for AVCS codes on 2011-2015 models, so on a Subaru the dealer should check for those first.
Most likely causes
Cause 1: Low oil level, old or sludged oil, or the wrong viscosity
Common general cause- Why it ranks here
- Phasers move on oil pressure; low level, sludge or the wrong grade slows them or stops them reaching the target.
- What would change this
- Rises if the oil is low, overdue or not the grade in the owner's manual.
Cause 2: Bank 2 intake oil control solenoid stuck or its screen blocked
Common general cause- Why it ranks here
- A stuck timing control solenoid is one of the listed causes, and debris can block its screen.
- What would change this
- Rises if the cam does not follow scan tool commands but recovers after cleaning or replacing the solenoid.
Cause 3: Engine computer logic (2023 Subaru Crosstrek, Impreza, Forester)
Supported by vehicle data- Why it ranks here
- Subaru released reprogramming for rare P0011 and P0021 on 2023 Crosstrek, Impreza and Forester. Status not verified.
- What would change this
- Rises on those models with no mechanical fault found.
Cause 4: Sticking cam phaser (bank 2 intake)
Possible — needs testing- Why it ranks here
- OBD rules require detecting phasers that do not reach the target, including stuck parts; a phaser is usually blamed after oil and solenoid check out.
- What would change this
- Rises if the solenoid works but the cam still does not move.
Cause 5: Worn timing chain, tensioner or guide
Possible — needs testing- Why it ranks here
- Listed as a cause; a stretched chain changes the baseline cam position on all cams.
- What would change this
- Rises with timing rattle and with correlation codes (P0016-P0019) also stored.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: With the engine off on level ground, check the oil level and condition, and confirm the oil grade matches the owner's manual.
IfOil is low, overdue, sludgy or the wrong viscosity
It meansCorrect the oil first, clear the code and drive; many cam timing codes return no further.
Points to: Low oil level, old or sludged oil, or the wrong viscosity
IfOil is full, fresh and the right grade
It meansLook at what the camshaft is actually doing.
Step 2: On a Subaru, ask a dealer whether the ECM update or AVCS diagnostic bulletin applies to the VIN.
IfAn ECM update applies and has not been done
It meansHave it reprogrammed, then clear the code and drive.
Points to: Engine computer logic (2023 Subaru Crosstrek, Impreza, Forester)
IfNo bulletin applies, or not a Subaru
It meansCheck how the cam responds.
Step 3: With the engine warm, compare desired and actual bank 2 intake cam angle on a scan tool, and command the bank 2 intake oil control solenoid if the tool allows.
Warning:Keep hands and tools away from belts and the cooling fan with the engine running.
IfCam angle does not follow commands
It meansThe solenoid, its screen or the phaser is not responding.
Points to: Bank 2 intake oil control solenoid stuck or its screen blocked
IfSolenoid works but the cam still lags or stays advanced
It meansThe phaser or timing drive is suspect.
Symptoms
- Check engine light on
- Rough idle, hard starting or reduced power
- Rattling noise from the engine Gets more serious: stop and have it checked.
Compare with: Rough idle with the check engine light on, Check engine light with loss of power
How to fix
Step 1: Check the oil level and top it up to the full mark with the grade listed in your owner's manual.
Warning:Engine off and on level ground; wait a few minutes for oil to drain back.
Step 2: If the oil is overdue or the wrong grade, change the oil and filter with the specified oil, clear the code and drive normally to see whether it returns.
Warning:Let the engine cool before draining; hot oil burns. Support the car on ramps or stands, never just a jack.
On your vehicle
SubaruYour car
2011–2023
Supported by vehicle dataOn 2023 Crosstrek and Impreza (and Forester under a companion bulletin), Subaru has ECM reprogramming for rare P0011/P0021; on 2011-2015 models it has a dedicated AVCS diagnostic bulletin. Ask a dealer before replacing parts.
09-105-23Status unverified
ECM reprogramming for rare P0011 and P0021
2023crosstrek, impreza · issued · NHTSA 10237262
New engine computer software to address rare P0011 and P0021 on 2023 Crosstrek and Impreza. Subaru issued a companion bulletin for the Forester.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
02-132-12RStatus unverified
Diagnosis and repair for AVCS-related DTCs P000A-P000D, P0011, P0014, P0021 and P0024
2011–2015impreza, forester, outback, legacy, brz, xv-crosstrek · issued · rev. R · NHTSA 10084253
Subaru diagnostic and repair procedure for its AVCS (variable valve timing) codes; the NHTSA summary gives only the title.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
Related codes
P0021 questions
Which side is bank 2?
Bank 2 is the side of a V6, V8 or flat engine that does not have cylinder 1. Inline four-cylinder engines have only bank 1, so P0021 normally appears on V or flat engines.
Sources and review
- Cal. Code Regs. tit. 13, § 1968.2 - Malfunction and Diagnostic System Requirements (OBD II)
- P0021 Code: 'A' Camshaft Position - Timing Over-Advanced (Bank 2)
- Variable Valve Timing
- 2001 Lincoln Continental Owner's Guide - Warning lights (Check engine)
- 2023 Integra Owner's Manual: Indicator, Coming On/Blinking
- ASE A1 study guide: VVT phaser diagnostics
- Subaru 09-105-23: ECM reprogramming for rare P0011 and P0021
- Subaru 02-132-12R: Diagnosis and repair for AVCS-related DTCs P000A-P000D, P0011, P0014, P0021 and P0024
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
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