P0021 on 2015-2021 Lincoln Navigator: 'A' Camshaft Position Timing Over-Advanced (Bank 2) Causes and Fixes

What's Unique About the 2015-2021 Lincoln NAVIGATOR

The 3.5L twin-turbo V6 engine (EcoBoost) in the Lincoln Navigator is notorious for VCT system issues. The system is highly sensitive to oil quality and maintenance schedules. Numerous Ford/Lincoln Technical Service Bulletins (TSBs) confirm that P0021 and related codes are often triggered by small debris in the oil causing the VCT solenoids to stick. Furthermore, the 2nd generation of this engine (2017+) is known for premature camshaft phaser failure, which can also cause this code, often accompanied by a distinct rattling noise on startup. These known failure points make regular, high-quality oil changes (e.g., every 5,000 miles) especially critical to prevent or delay these common timing-related issues.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle. 👇

Generation note: This range covers two generations of the Lincoln Navigator: the third generation (2015-2017) and the fourth generation (2018-2021). Both use a 3.5L twin-turbo V6. While the root cause is often VCT solenoids on both, the first generation (pre-2017) was more prone to timing chain stretching, while the second generation (2017+) is more known for camshaft phaser failures, sometimes at low mileage. The fundamental diagnostic approach for P0021 remains similar across both.

Symptoms You May Notice

• Check Engine Light is on
• Rough or unstable idle, sometimes stalling at stops
• Engine hesitation or loss of power, especially during acceleration or under load
• Reduced fuel economy
• Rattling noise from the engine, especially on cold starts (a classic sign of cam phaser issues)
• Difficulty starting the engine
• Hard or violent shifting as the powertrain struggles to compensate for incorrect timing

Most Likely Causes

1. Low or Dirty Engine Oil 🔴 High Probability The VCT system is hydraulic and relies on clean oil at the correct pressure. The manufacturer has issued multiple TSBs noting that debris in the oil can cause VCT solenoids to stick. Owners on forums frequently report that extending oil change intervals beyond 5,000 miles can lead to these issues.
   How to confirm: Check the engine oil level on the dipstick and inspect its condition. If the oil is low, excessively dark, or past its recommended change interval, it is the first and easiest thing to address.
   Typical fix: Perform an engine oil and filter change using the manufacturer-recommended full synthetic oil (SAE 5W-30) and a high-quality filter. Clear the codes and see if the issue returns.
   Est. part cost: $50-$100
2. Faulty VCT Solenoid (Bank 2 Intake) 🔴 High Probability → Shop Engine Variable Valve Timing (VVT) Solenoid As highlighted in TSBs SSM 50067 and TSB 16-0093, these solenoids are a common failure point, often getting stuck due to oil contamination or internal failure.
   How to confirm: A technician can monitor the solenoid's operation with a scan tool, commanding it on and off to check for a response. A common DIY method is to swap the Bank 2 intake solenoid with the Bank 2 exhaust solenoid. Clear codes and drive. If the code changes to P0022 (over-retarded), the solenoid is confirmed faulty. The Bank 2 solenoids are on the driver's side valve cover.
   Typical fix: Replace the Bank 2 (driver's side) intake VCT solenoid. The intake solenoid is typically the one closer to the intake manifold.
   Est. part cost: $90-$130
3. Damaged Camshaft Phaser 🟡 Medium Probability → Shop Engine Camshaft The 2nd generation 3.5L EcoBoost (2017+) is particularly known for cam phaser failures, which can cause a loud rattling noise on startup and set timing codes like P0021. This can happen even on well-maintained, low-mileage vehicles.
   How to confirm: This is a more involved diagnosis. A prominent cold-start rattle is a strong indicator. 🎬 Watch: Hear the classic cam phaser rattle and learn the cause. If replacing the VCT solenoid and changing the oil doesn't fix the issue, the phaser is the next likely culprit. This requires significant engine disassembly to inspect and replace.
   Typical fix: Replace the camshaft phasers, which is a major repair that should also include replacing the timing chains, guides, and tensioners. A dealer quote for this job can be $3,500-$4,500.
   Est. part cost: $400-$800 for a full timing kit

Rare But Worth Checking

• Stretched Timing Chain or Failed Tensioner: → Shop Engine Timing Chain More common on the 1st generation 3.5L EcoBoost (pre-2017), a stretched timing chain can cause camshaft and crankshaft correlation errors, leading to P0021 and often P0018. This is a serious mechanical issue requiring a full timing job.
• Wiring or Connector Issue to the VCT Solenoid: → Shop Engine Variable Valve Timing (VVT) Solenoid Damage to the wiring harness or a corroded/loose connector can prevent the PCM from controlling the solenoid correctly. A visual inspection and continuity test with a multimeter can confirm this.
• PCM Software Glitch: In some cases, the PCM may have outdated software that incorrectly flags a timing issue. A dealer or qualified shop can check for and apply any available software updates. TSBs like 21B10 involved a PCM reprogram to help mitigate phaser noise.

Diagnosis Steps

1. Verify the Check Engine Light is on and scan for P0021 and any other codes. Note codes like P0018, which point more strongly to mechanical timing.
2. Check the engine oil level and condition. If low, dirty, or past due for a change, perform an oil and filter change with full synthetic SAE 5W-30 oil. This is the cheapest and easiest first step and can sometimes resolve the issue.
3. Using a capable scan tool (like FORScan), monitor the desired vs. actual camshaft angle for Bank 2 Intake (VCTADV2). 🎬 Watch: A deep dive into how these phaser problems are diagnosed. Also monitor the VCT error percentage (VCT_ERR2). A large and persistent error indicates a problem. Command the Bank 2 intake VCT solenoid on and off to check for a response in cam angle.
4. Inspect the wiring and connector for the Bank 2 intake VCT solenoid (driver's side valve cover) for any signs of damage, corrosion, or loose connections.
5. Perform a 'solenoid swap'. Unplug and remove the Bank 2 intake and exhaust VCT solenoids. Swap their positions, clear the codes, and drive the vehicle. If the code changes to P0022 (Bank 2 'A' Camshaft Position Timing Over-Retarded), the solenoid you moved to the exhaust position is faulty and needs replacement.
6. If the solenoid appears to be working and the oil is clean, the issue is likely mechanical. Listen for a startup rattle. A rattling noise strongly points towards failing camshaft phasers and/or a stretched timing chain. This is an advanced repair best left to a professional.

Parts You'll Likely Need

• Engine Variable Valve Timing (VVT/VCT) Solenoid (Bank 2 Intake) (OEM #AT4Z-6M280-B) — This is the most common point of failure for code P0021 on this engine, as confirmed by multiple manufacturer TSBs. It gets stuck due to oil debris or internal failure.
  Trusted brands: Motorcraft, Dorman, SKP
  OEM price range: $60-$86
  Aftermarket price range: $45-$75
• Engine Variable Valve Timing (VVT/VCT) Solenoid (Bank 2 Exhaust) (OEM #AT4Z-6M280-A) — Needed for performing the 'swap test' to confirm if the intake solenoid is the faulty component. It's wise to have on hand or know the part number before starting the diagnosis.
  Trusted brands: Motorcraft, Dorman
  OEM price range: $60-$85
  Aftermarket price range: $45-$75

Related Codes That Often Appear With This One

• P0011 — This is the equivalent code for Bank 1 (passenger side). Seeing both may indicate a systemic issue like very low/dirty oil affecting both sides of the engine.
• P0018 — This code indicates a 'Crankshaft Position - Camshaft Position Correlation' error on Bank 2. It often appears with P0021 and strongly suggests a mechanical timing problem like a stretched chain or failed phaser, as the misalignment is significant (1 tooth or greater).
• P052B — This code relates to 'Cold Start 'A' Camshaft Position Timing Over-Retarded Bank 2', indicating the problem is most apparent during cold starts, which is common for oil-pressure related VCT and phaser issues.
• P0302 — A misfire code for a cylinder on Bank 2 (e.g., P0302, P0304, P0306). Incorrect cam timing can disrupt the combustion process in the cylinders of the affected bank, leading to misfires.

Technical Service Bulletins (TSBs) & Recalls

• SSM 50067: Notes that various VCT codes including P0021 may be due to small debris causing the VCT solenoid to stick. Recommends cycling the solenoid with a scan tool to try and clear it before replacement.
• SSM 54366: Mentions P0021 and directs technicians to specific diagnostic tests (Pinpoint Test HK) in the workshop manual.
• SSM 47170: Similar to SSM 50067, attributes P0021 to debris in the VCT solenoid.
• TSB 16-0093 (supersedes TSB 16-0038): Specifically addresses P0021 and other timing codes on low-mileage (under 2000 miles) 2016 vehicles, including the Navigator. The prescribed action is to replace the affected VCT solenoid.
• TSB160038: The earlier version of TSB 16-0093, calling out the 3.5L GTDI engine for exhibiting P0021 and other codes at very low mileage and instructing dealers to replace the solenoids.

Platform-Specific Known Issues

• The 3.5L GTDI (EcoBoost) engine is the subject of several TSBs (SSM 50067, TSB 16-0093) that directly link codes like P0021 to VCT

Mechanic-Grade Diagnostic Values

• VCT Solenoid Resistance — expected: 1-2 ohms (for general GTDI injectors, VCT solenoids are similar but spec may vary slightly). Failure: A reading of 22 Ohms was noted in one case of a failed solenoid, indicating a degrading internal coil. Any significant deviation from the low single-digit ohm range warrants suspicion.
• FORScan VCT PIDs at Hot Idle — expected: VCT_EXH (Exhaust) = 0 degrees, VCT_INT (Intake) = 20 degrees, VCT_DIF (Difference) = 0 degrees.. Failure: Significant deviation from these values at hot idle, even without a check engine light, can indicate a pending problem in the Ti-VCT system.

Scan Tool Commands That Help

• FORScan: Monitor VCT PIDs (VCT_INT2_ACT, VCT_INT2_DSD, VCT_ERR2) — Use these Parameter IDs (PIDs) to diagnose P0021. VCT_INT2_ACT is the actual intake cam angle for Bank 2. VCT_INT2_DSD is the desired angle commanded by the PCM. VCT_ERR2 is the difference between them. A large, persistent value for VCT_ERR2 confirms a timing control problem on that camshaft.
• FORScan: VCT Solenoid On/Off Command — This bidirectional control allows the technician to manually command the VCT solenoid on and off while monitoring the actual camshaft angle PID (VCT_INT2_ACT). A lack of change in the cam angle when the solenoid is commanded indicates a stuck solenoid, clogged oil passage, or wiring issue.

Wiring & Ground Locations

• VCT Solenoid Connectors — On the top of the valve covers. Bank 2 (driver's side) has two solenoids, one for intake and one for exhaust. The connectors are physically close and can be accidentally swapped during a repair.. A confirmed repair case showed that swapping the intake and exhaust solenoid connectors on Bank 2 after a phaser job resulted in codes P0021 and P0025. The PCM was commanding the wrong solenoid, leading to incorrect timing.
• Power Distribution Box — Located in the engine compartment.. This box contains fuses and relays for critical engine systems, including the Powertrain Control Module (PCM) which controls the VCT solenoids. While a blown fuse is not a common cause for a single VCT code, checking relevant fuses (e.g., PCM power) is a basic step in electrical diagnosis.
• Factory Wiring Diagrams — Available for purchase as standalone manuals or as part of a factory service manual.. For diagnosing persistent electrical issues, such as an open or short in the VCT solenoid circuit (VPWR or control wire), a factory wiring diagram is essential for tracing wires, identifying connector pinouts, and locating ground points.

Real Owner Repair Stories

• Ford F150 Forum (2017 F-150 3.5L EcoBoost with 99k miles) — Check Engine Light came on after driving, with codes P0021 and P0025. No rough idle or stalling.
  ❌ Tried (didn't work) Swapping the VCT solenoids with the original ones., Verifying mechanical timing was correct at TDC.
  ✅ What actually fixed it The VCT solenoid electrical connectors on the driver's side valve cover had been reversed (swapped between intake and exhaust). Correcting the connector positions resolved the codes.
• Ford F150 Forum (2018 F-150 3.5L EcoBoost) — Reduced power, codes P0018 and P0021 appeared.
  ❌ Tried (didn't work) The user did not list preliminary steps but took it to a dealer.
  ✅ What actually fixed it The dealer replaced the cam phasers, which resolved the issue. This occurred after a previous phaser replacement at 50k miles, indicating a recurring problem on the vehicle.

OEM Part Supersession History

• AT4Z-6M280-A (Bank 2 Exhaust) → No clear supersession found, this part number appears current for the application.
• AT4Z-6M280-B (Bank 2 Intake) → No clear supersession found, this part number appears current for the application.
  Heads up: Note: The 3.5L EcoBoost uses different part numbers for intake/exhaust solenoids on Bank 1 vs Bank 2. TSB 16-0038 specifies AT4Z-6M280-B for the Bank 2 Intake. Ensure the correct part is used for the specific position.
• FT4Z-6M280-A → FT4Z-6M280-B — Part revision or update by manufacturer.
  Heads up: This part number applies to some 2nd Gen 3.5L EcoBoost engines. Always verify the correct part number by VIN.

Model Year Variations Within This Range

• 2015-2017 (Gen 1 3.5L EcoBoost): These engines used a single, long primary timing chain and were known to be more susceptible to timing chain stretch over time, which could cause P0021, often paired with correlation codes like P0018. They also featured direct injection only, making them prone to carbon buildup on intake valves.
• 2018-2021 (Gen 2 3.5L EcoBoost): The engine was significantly redesigned. It features a dual-chain system (one primary, two secondary), redesigned VCT phasers, and a dual fuel injection system (port and direct) to mitigate intake valve carbon buildup. While the chain design was improved, this generation is widely known for premature cam phaser failure, causing startup rattle and timing codes.