P0021 on Mercedes-Benz: How to Diagnose & Fix
Intake Camshaft Position Timing - Over-Advanced (Bank 2)
3 Mercedes-Benz models · 3 documented issues · 1 critical · $600-$4,000 repair
P0021 on Mercedes-Benz by model: symptoms, diagnosis and fix
On the M276 3.5L V6 (and the related M278 V8) the four camshaft adjusters — the variable-valve-timing phasers bolted to the ends of the cams — wear internally. The locking pin and vane chambers lose their ability to hold position, and oil bleeds out of the adjuster while the car sits. On the next cold start the cam is unsupported for the first second or two of cranking until oil pressure builds, producing a loud metallic rattle from the front of the engine. As wear progresses the adjuster can no longer hold commanded timing and the ECU logs cam/crank correlation and timing-over-advanced faults. Clogged camshaft adjuster magnets (solenoids) and a stretched timing chain often accompany the failure and are commonly misdiagnosed as the sole cause. Owners frequently report the dealer first replacing solenoids or doing an oil change before the adjusters themselves are condemned.
Common Symptoms
- Loud metallic rattle for 1-3 seconds on cold start
- Rattle worse after the car sits overnight or several days
- Check engine light
- Rough idle when cold
- Reduced power / limp mode in advanced cases
- Noise diminishes once oil pressure builds
How to Fix
Replace the camshaft adjusters — all four, not just the noisy bank — with the updated Mercedes parts, along with the camshaft adjuster magnets/solenoids. Inspect the timing chain, tensioner and guide rails while the front cover is open and replace them if the chain shows stretch, since a worn chain will destroy new adjusters. The engine must be re-timed and the adaptations reset. Use only the specified MB 229.5/229.51 oil at the correct viscosity and keep to shorter oil-change intervals, as degraded oil accelerates adjuster wear.
Sources for this issue (3)
The SLC 43 AMG's M276 DE30LA 3.0L biturbo V6 commonly develops a loud rattle for a few seconds at cold start as the camshaft adjusters (variable valve timing solenoid units) and their solenoid magnets wear, losing the ability to hold oil pressure/timing on shutdown. The engine has four adjusters; when worn they produce the characteristic startup rattle and can set camshaft-correlation/position fault codes, with risk of extended crank, rough running, and timing deviation if left unaddressed. This is a well-documented M276 trait, typically appearing past ~60k-100k miles.
Common Symptoms
- Loud rattle for a few seconds at cold start
- Check engine light
- Extended cranking on start
- Rough idle
- Variable valve timing fault
How to Fix
Confirm with stored DTCs; the accepted fix is replacing all four camshaft adjusters (and the solenoid magnets) rather than chasing one. Parts for all four adjusters run roughly $500-$600, plus labour and a crankshaft-holding tool; budget more at a dealer. Address promptly, as prolonged rattle can damage chain/guide components.
Sources for this issue (3)
The W166 GLE 350 and GLE 400 (2016-2018, M276 3.0L/3.5L V6) share the well-known M276 camshaft-adjuster problem. The variable-valve-timing camshaft adjusters and their magnets/solenoids wear, allowing the cams to fall out of time. Symptoms include a 2-3 second rattle on cold start, rough running, and check-engine codes such as P0010-style adjuster faults; owners report codes like P002177 with cams found advanced/out of time. Left unaddressed, a worn adjuster can cause poor timing control and driveability problems.
Common Symptoms
- 2-3 second rattle on cold start
- rough idle
- check engine light
- rough running / hesitation
- cam timing fault codes
How to Fix
Read the cam-correlation/adjuster DTCs and inspect the intake and exhaust camshaft adjusters and adjuster magnets. Replace worn camshaft adjusters (often with an updated timing chain kit and tensioner) and the adjuster solenoids on the affected bank, then re-verify cam timing. Using correct-spec oil and timely oil changes helps prevent adjuster sludging.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- FCP/Febi M276 bank-1 intake camshaft-adjuster repair kit 176728OEMFCP 176728
Mechanically confirmed bank-1 intake adjuster failure on the cataloged 2016-2018 GLE350 M276.955 branch Fitment/availability: The inspected direct U.S.
- OE-supplier camshaft-adjuster magnet/solenoid 2761560790OEMOE Supplier 2761560790
Electrically or leak-confirmed external adjuster magnet on the cataloged GLE350 branch Fitment/availability: The inspected direct U.S.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (2)
P0021 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0021 mean on a Mercedes-Benz?
P0021 stands for "Intake Camshaft Position Timing - Over-Advanced (Bank 2)." P0021 means the engine computer detected that the intake camshaft on bank 2 is timed too far advanced and won't return to its commanded position. Most modern engines use variable valve timing (VVT), where an oil-pressure-driven actuator rotates the camshaft to optimize power and efficiency; the PCM compares the camshaft's actual position to its target. When the cam stays over-advanced beyond an acceptable limit, this code sets. Bank 2 refers to the side of the engine that does not contain cylinder number one. You may notice rough idle, reduced performance, or lower fuel economy. On Mercedes-Benz it is documented across 3 models: E-Class, SLC, GLE.
What are the most common causes of P0021?
The most common causes of P0021 are: Dirty or low engine oil restricting the VVT system, Stuck or failed camshaft oil control valve (VVT solenoid) on bank 2, Clogged VVT solenoid screen or oil passage, Faulty camshaft position actuator / phaser, Wiring or connector fault at the VVT solenoid, Camshaft or crankshaft position sensor problems, Worn timing chain, guides, or stretched chain altering cam timing. The specific cause varies by vehicle.
How much does it cost to fix P0021 on a Mercedes-Benz?
Published repair estimates on Mercedes-Benz range from $600 to $4,000 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0021 on a different make?
View P0021 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.