P0021 on 2016-2019 Cadillac CT6: Cam Timing Causes and Fixes

What's Unique About the 2016-2019 Cadillac CT6

The cause of P0021 on the Cadillac CT6 depends entirely on the engine. For the 2.0L Turbo (LTG) I4 engine, which only has one cylinder bank, a P0021 'Bank 2' code is a known software anomaly or 'ghost code' and does not indicate a mechanical fault on a non-existent bank. For the 3.6L (LGX) and 3.0L (LGW) V6 engines, the code points to a legitimate issue, often a software glitch related to the auto stop/start system, a bad VVT solenoid, or simply low engine oil. GM issued a preliminary bulletin (PIP5568E) investigating this exact code appearing with others (P0011, P0014, P0024), highlighting a known software issue across these engines where the ECM reports incorrect cam positions after a restart.

Diagnostic Flowchart

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

Symptoms You May Notice

• Check Engine Light is on
• Rough or unstable idle
• Engine stalling, especially after an auto stop/start event
• Hesitation or stumbling during acceleration
• Reduced engine power
• Decreased fuel economy
• Engine rattling or knocking noises (in cases of severe oil starvation or timing chain issues)

Most Likely Causes

1. Low or Dirty Engine Oil (All Engines) 🔴 High Probability The VVT system is hydraulic and extremely sensitive to oil pressure and cleanliness. Sludge or low levels can prevent the camshaft phasers from operating correctly. This is the most common cause across all GM vehicles with VVT.
   How to confirm: Check the engine oil dipstick. If the level is low or the oil is dark, gritty, or past its service interval, this is the likely cause. A Reddit user with the same LGX engine in a 2017 Camaro confirmed that 'dirty and sludgy' oil triggered codes P0011 and P0021, which were resolved by a dealership oil change.
   Typical fix: Perform an engine oil and filter change using the correct specification oil (ACDelco dexos1 Gen 2 Full Synthetic 5W-30). Clear codes and drive.
   Est. part cost: $50-$100
2. ECM Software Anomaly (2.0L LTG Engine) 🔴 High Probability As documented in GM TSB #PIP5568E, the 2.0L engine can set a 'Bank 2' code erroneously due to a software glitch, often after an auto stop/start cycle. The ECM fails to properly synchronize cam position data on restart and reports a fault for a non-existent bank.
   How to confirm: The presence of a Bank 2 code (P0021 or P0024) on an inline-4 engine is the primary indicator. It may appear with other 'ghost' codes like P0011 or P0014.
   Typical fix: The initial fix recommended by GM was to clear the codes and return the vehicle to the customer. If the problem persists, an ECM software update at a dealership is the permanent solution.
   Est. part cost: $0-$200
3. Faulty Intake Camshaft Position Actuator Solenoid (V6 Engines) 🔴 High Probability → Shop Engine Camshaft These solenoids can become clogged with debris from engine oil or fail electrically, causing them to stick in the advanced position. They are a very common failure item on the GM V6 🎬 See this walkthrough for replacing the VVT actuator solenoid engine family.
   How to confirm: Swap the Bank 2 (driver's side) intake solenoid with the Bank 2 exhaust solenoid. They are typically identical parts. Clear codes and drive. If the code changes to P0024 (Exhaust Cam Over-Advanced), the solenoid is confirmed bad. 🎬 Watch: How to diagnose and fix a Bank 2 solenoid The Bank 2 solenoids are located on the front of the cylinder head on the driver's side.
   Typical fix: Replace the Bank 2 (driver's side) intake camshaft position actuator solenoid. Use OEM part number 12687954 for the intake solenoid.
   Est. part cost: $40-$90
4. ECM Software Anomaly (V6 Engines) 🟡 Medium Probability TSB PIP5568E and subsequent service update N192266190 confirm a software issue causing multiple cam codes (P0011, P0014, P0021, P0024) to set after an auto stop/start event. The glitch relates to the control of 'mid-park' cam phasers used for smoother restarts.
   How to confirm: The key symptom is multiple camshaft codes appearing together, often with no other obvious mechanical fault, especially after a stop-start cycle. A dealer can check the vehicle's VIN against TSB N192266190 to see if the software update applies.
   Typical fix: Reprogram the Engine Control Module (ECM) with updated software at a GM dealership. This is covered under warranty for affected vehicles.
   Est. part cost: $100-$250 (Labor)

Rare But Worth Checking

• Clogged VVT Solenoid Oil Filter Screen: → Shop Engine Oil Filter Adapter In the oil passage leading to the VVT solenoid, there is a small, thimble-shaped mesh filter. This screen can become clogged with sludge, starving the solenoid of oil pressure. This can cause P0021 to persist even after replacing the solenoid and changing the oil. The screen must be removed and cleaned or replaced.
• Stretched Timing Chain or Failed Tensioner (V6 Engines): → Shop Engine Timing Chain While less common on the LGX/LGW engines than their predecessors, significant mileage or neglected oil changes can lead to timing chain stretch. This is a major repair and is usually accompanied by rattling noises, especially on startup.
• Failed Camshaft Phaser (V6 Engines): → Shop Engine Camshaft The mechanical gear (phaser) that the solenoid controls can fail, getting stuck in the advanced position. This is less common than a solenoid failure and is a more involved and expensive repair.
• Sticking Camshaft Park Lock Solenoid (V6 Engines): → Shop Engine Camshaft Per GM TSB PIP5730B, the LGX engine uses separate 'park lock' solenoids for the stop/start system. If the intake park lock solenoid sticks, it can cause cam timing codes like P0021, sometimes without other symptoms.

Diagnosis Steps

1. Check Engine Oil: Verify the oil level is full and the oil is clean and of the correct viscosity (dexos1 5W-30). If low or dirty, perform an oil and filter change, clear the code, and see if it returns. This is the most common and cheapest fix.
🎬 Watch: Two simple DIY methods to clear the P0021 code
2. Scan for Other Codes: Check if P0021 is alone or present with P0011, P0014, or P0024. A group of these codes strongly suggests the software issue mentioned in TSB PIP5568E, especially if they appeared after an auto-stop event.
3. Identify Your Engine: If you have the 2.0L I4 engine, the code is a known software glitch. Clear the code. If it returns frequently, consult a dealer about a potential ECM software update.
4. Test the Solenoid (V6 Engines): If the oil is good and the code is isolated to P0021, test the Bank 2 intake VVT solenoid. The solenoids are on the driver's side front of the engine. Swap the intake solenoid (upper) with the exhaust solenoid (lower). Clear codes and drive. If the code changes to P0024, the solenoid is bad and needs replacement.
5. Check for TSBs/Software Updates: Contact a GM dealership with your VIN. Ask them to check for service update N192266190 or other applicable ECM reprogramming campaigns related to camshaft timing codes.
6. Inspect VVT Oil Filter Screen (V6 Engines): If a new solenoid doesn't fix the issue, the next step is to inspect the small oil filter screen in the cylinder head passage leading to the solenoid. If it's clogged with debris, clean or replace it.
7. Advanced Mechanical Diagnosis: If all else fails, the issue may be a stretched timing chain, a faulty camshaft phaser, or a sticking park lock solenoid, which requires professional diagnosis.

Parts You'll Likely Need

• Intake Camshaft Position Actuator Solenoid (V6 Engines) (OEM #12687954) — This is the most common mechanical part to fail on the LGX/LGW V6 engines, causing the camshaft timing to stick. Note: The exhaust solenoid is part number 12687955. The older part number 12655420 is often listed but is incorrect for the LGX engine.
  Trusted brands: ACDelco (Genuine GM), Delphi
  OEM price range: $60-$90
  Aftermarket price range: $40-$70
• Engine Oil and Filter — Low or dirty engine oil is the leading cause of all VVT system faults, including P0021. Use a full synthetic oil meeting the GM dexos1 Gen 2 5W-30 specification.
  Trusted brands: ACDelco, Mobil 1
  OEM price range: $70-$100
  Aftermarket price range: $50-$80

Related Codes That Often Appear With This One

• P0011 — This is the same over-advanced code for Bank 1. If both appear, it points to a systemic issue like low oil or the ECM software glitch affecting both banks.
• P0014 — Exhaust cam timing code for Bank 1. TSB PIP5568E specifically notes that P0011, P0014, P0021, and P0024 often set together due to the software anomaly.
• P0024 — Exhaust cam timing code for Bank 2. If this appears after swapping the intake and exhaust solenoids on Bank 2, it confirms the original intake solenoid was faulty. It can also appear with P0021 due to the software glitch.

Technical Service Bulletins (TSBs) & Recalls

• PIP5568E: Preliminary investigation into P0011, P0014, P0021, and P0024 setting together, identifying a software anomaly as a likely cause, especially after auto stop/start events.
• N192266190: While for other GM models with the same 3.6L LGX engine (like the Cadillac XT5 and Chevy Traverse), this Service Update provides the ECM reprogramming fix for the issue described in PIP5568E.
• PIP5730B: Identifies a sticking or broken Intake Camshaft Position Actuator Park Lock Solenoid as a potential cause for cam timing codes on the 3.6L LGX engine.

Platform-Specific Known Issues

• A known software anomaly can cause P0021 to set, especially on the 2.0L LTG engine where Bank 2 does not physically exist. On V6 models, a similar software glitch can set multiple cam codes at once after an auto-stop/start event.

Mechanic-Grade Diagnostic Values

• Camshaft Position Actuator (VVT) Solenoid Resistance — expected: 6.0 to 12.5 Ohms. Failure: A reading of 0 Ohms (short circuit) or infinite/Mega Ohms (open circuit) indicates a failed solenoid coil.
• Camshaft Position Variance (Scan Tool Live Data) — expected: Near 0° at idle.. Failure: A consistent deviation of more than 4-5 degrees between the desired and actual camshaft position indicates a mechanical timing issue like a stretched chain or faulty phaser.
• System Voltage at Battery (Engine Running) — expected: ~14.5V. Failure: Low system voltage (e.g., 11.8V) can cause erratic behavior from sensors and actuators, leading to false codes.

Scan Tool Commands That Help

• GDS2 (GM Dealer Tool) / Professional Scan Tool: Camshaft Position Actuator Active Test — This bidirectional control allows a technician to manually command the Bank 2 intake solenoid ON and OFF while the engine is idling. If the solenoid is working and oil passages are clear, the engine's idle should stumble or change noticeably. No change in idle points to a faulty solenoid, a clog in the oil passage, or a seized cam phaser.

Wiring & Ground Locations

• ECM Connector C1, Pin 12 — On the Engine Control Module (ECM).. This is the specific pin for the Camshaft Position Actuator Solenoid Control for Intake Bank 2. Testing for signal at this pin can confirm if the ECM is sending the command to the solenoid. The wire color is typically Orange/Black.
• Engine Ground Straps — On many GM 3.6L V6 engines, ground straps are attached to the front of the cylinder heads near the VVT solenoids. Another critical ground (G102) is located at the left rear of the engine and grounds the ignition coils.. A poor engine block ground can cause incorrect readings and faulty operation of the VVT solenoids and camshaft position sensors, which rely on a stable ground reference to function correctly.
• Underhood Fuse Block — Located on the driver's side of the engine compartment for the 2.0L, 3.0L, and 3.6L engines.. This fuse block contains the fuses and relays that supply power to the Engine Control Module and its related components, including the VVT solenoids. A fault here could cut power to the system.

Real Owner Repair Stories

• Reddit user in r/MechanicAdvice (2018 Chevrolet Colorado with 3.6L V6 (LGX engine family)) — Check Engine Light with code P0024 (Bank 2 Exhaust, a related code).
  ❌ Tried (didn't work) Initial diagnosis pointed towards a faulty camshaft position actuator solenoid.
  ✅ What actually fixed it The root cause was a corroded negative battery terminal causing low system voltage (11.8V). Cleaning the terminal and post restored normal voltage (14.5V running) and resolved the code without replacing any VVT parts.

OEM Part Supersession History

• 12655420 → 12679099, 12687954 (application dependent) — Part revision and consolidation.
  Heads up: Part number 12655420 is frequently listed for GM VVT solenoids but is noted as incorrect for the later LGX V6 engine. Using the wrong part can result in improper function. The correct intake solenoid for the LGX is typically 12687954. Always verify with VIN.