P0021 on 2017-2019 Buick LaCrosse 3.6L: VVT Solenoid, Oil, and TSB Causes

What's Unique About the 2017-2019 Buick LaCrosse

The LGX V6 engine in this LaCrosse has two very specific issues that often trigger a P0021 code, which are not typical mechanical failures. First, a software glitch, particularly after an engine stop/start event, can falsely set this code, requiring a dealer to reprogram the computer as outlined in GM Service Update N192266190. Second, a special part called the 'Intake Camshaft Position Actuator Park Lock Solenoid,' related to the stop/start system, can stick and cause this code without any other symptoms, a cause often missed during normal diagnosis and documented in TSB PIP5730B.

Symptoms You May Notice

• Check Engine Light is on
• Rough or unstable idle
• Engine may hesitate or stumble during acceleration
• Reduced engine power
• Decreased fuel economy
• Engine may stall, especially when coming to a stop or during an auto-start event
• Rattling noise from the engine on startup, which could indicate a more serious timing chain issue

Most Likely Causes

1. Low or Dirty Engine Oil 🔴 High Probability The Variable Valve Timing (VVT) system is hydraulic and extremely sensitive to oil pressure and cleanliness. Sludge or low levels can prevent the camshaft phasers from operating correctly. Some owners of the LGX engine report minor oil consumption, making it critical to check levels regularly.
   How to confirm: Check the engine oil level on the dipstick and examine its color and consistency. If it is below the 'full' mark, dark black, or feels gritty, it needs to be changed. A Reddit user with the same LGX engine confirmed an oil change fixed their P0011 and P0021 codes.
   Typical fix: Perform an engine oil and filter change using a full synthetic 5W-30 oil that meets GM's dexos1 Gen 2 specification. Clear the code and see if it returns.
   Est. part cost: $50-$90
2. Engine Control Module (ECM) Software Issue 🔴 High Probability → Shop Engine Control Module (ECM) A specific software issue, documented in GM service update N192266190, can cause this code to set after an auto stop/start event, particularly on 2018 models. Manufacturer bulletin #N192266190 notes that while the vehicle is stopped, this condition can cause the engine to run rough, run at reduced power, or, in rare cases, stall.
   How to confirm: Contact a GM dealership with your VIN and ask if Service Update N192266190 is open or applies to your vehicle. This is especially likely if the code appears with P0011, P0014, and P0024 after a stop/start. The update is for certain 2018 LaCrosse, Enclave, Cadillac XT5, and Chevy Traverse vehicles.
   Typical fix: A GM dealer will reprogram the Engine Control Module (ECM). This is covered at no charge if the service update is active for your vehicle and it is within the New Vehicle Limited Warranty period.
   Est. part cost: $0
3. Faulty Intake Camshaft Position Actuator Solenoid (Bank 2) 🟡 Medium Probability → Shop Engine Camshaft These solenoids (also called VVT or oil control valves) are a common failure point on many modern engines. They can become clogged with debris from dirty oil or fail electrically, preventing proper oil flow to the cam phaser.
   How to confirm: After checking oil and TSBs, a common diagnostic step is to swap the Bank 2 intake solenoid with the Bank 2 exhaust solenoid (as they are the same part). Clear the codes and drive. If the code changes to P0024 (Exhaust Camshaft, Bank 2), the solenoid is confirmed faulty. You can also test the solenoid's resistance with a multimeter; a healthy solenoid will typically read between 8 and 12 ohms. 🎬 See how to test and fix the P0021 fault code.
   Typical fix: Replace the Bank 2 intake camshaft position actuator solenoid. It is located on the front of the engine and is held in by a single 10mm bolt. 🎬 Watch: Step-by-step VVT solenoid replacement on the LGX engine.
   Est. part cost: $35-$75

Rare But Worth Checking

• Sticking Intake Camshaft Position Actuator Park Lock Solenoid Valve: → Shop Engine Camshaft Documented in GM TSB PIP5730B, this is a separate, smaller solenoid related to the stop/start system that can stick and cause P0021, often without other symptoms. Standard diagnostics for P0021 do not typically check this part, so it's easily missed. The fix is to inspect and replace the park lock solenoid valves.
• Stretched Timing Chain: → Shop Engine Timing Chain While a much more common issue on the older LLT 3.6L V6, a stretched timing chain can still occur on the LGX, especially with high mileage or a history of infrequent oil changes. This is a major, expensive repair and is usually accompanied by a rattling noise on cold starts and potentially other timing codes like P0008 or P0009.
• Failing Oil Pump: In some cases, the oil pump itself can fail to provide adequate pressure to the VVT system, triggering timing codes. An owner of a Chevy Colorado with the same LGX engine reported that P0021 returned after an oil change and was only permanently fixed by replacing the oil pump.
• Simultaneous Timing Faults: Bulletin #PIP5568E notes an investigation into the cause and correction for a group of DTCs (P0011, P0014, P0021, P0024) setting together, which may also involve drivability concerns.

Diagnosis Steps

1. Check Engine Oil: Verify the oil level is full and the oil is clean. If low or dirty, perform an oil and filter change with full synthetic 5W-30 dexos1-approved oil. Clear the code and test drive.
2. Check for TSBs: Contact a GM dealer with your VIN to check for Service Update N192266190 (ECM reprogram) and TSB PIP5730B (park lock solenoid). If either is open, follow the dealer's recommendation as this is the most likely fix.
3. Inspect Solenoid Wiring: Visually inspect the connector and wiring for the Bank 2 (front, radiator side) intake VVT solenoid for any signs of damage, corrosion, or loose connections.
4. Swap Solenoids (Diagnostic): The intake and exhaust solenoids on the LGX engine are identical. Carefully swap the Bank 2 intake solenoid with the Bank 2 exhaust solenoid. Clear the codes and drive the vehicle. If the code changes from P0021 to P0024, you have confirmed the solenoid is faulty.
5. Replace Solenoid: If the solenoid is confirmed bad, replace it. The part is held by a single 10mm bolt and is accessible on the front of the engine.
6. Inspect Park Lock Solenoids: If the code persists, follow the guidance in TSB PIP5730B and inspect the Intake Camshaft Position Actuator Park Lock Solenoid Valves.
7. Seek Professional Help: If none of the above steps resolve the issue, the problem may be more complex, such as a clogged oil passage, a failing oil pump, or a mechanical timing issue (phaser, timing chain), which requires professional diagnosis.

Parts You'll Likely Need

• Intake Camshaft Position Actuator Solenoid (OEM #12679099) — This solenoid is the most common mechanical part to fail or clog, causing the timing to be over-advanced. The four solenoids on the LGX engine are often identical. Part number 12679099 is a common replacement for earlier numbers like 12655420.
  Trusted brands: ACDelco, GM Genuine Parts, Delphi
  OEM price range: $45-$75
  Aftermarket price range: $25-$50
• Engine Oil and Filter — Low or dirty oil is a primary cause of VVT system faults. Using the correct specification is critical.
  Trusted brands: Mobil 1, Pennzoil, Valvoline (must meet dexos1 Gen 2 spec)
  OEM price range: $50-$90
  Aftermarket price range: $50-$90

Related Codes That Often Appear With This One

• P0011 — This is the identical code but for Bank 1 (firewall side). If both P0011 and P0021 are present, it strongly points to a systemic issue like low/dirty oil or the ECM software glitch affecting the entire engine. Bulletin #PIP5568B indicates an investigation into why these codes often set together.
• P0024 — This code is for the exhaust camshaft on the same bank (Bank 2). If P0021 and P0024 appear together, it suggests a problem specific to Bank 2, like an oil flow issue to that cylinder head. It will also appear if you swap a bad intake solenoid to the exhaust position for diagnosis.
• P0014 — This is the exhaust camshaft code for Bank 1. TSB N192266190 explicitly states that the software issue can cause P0011, P0014, P0021, and P0024 to set.

Technical Service Bulletins (TSBs) & Recalls

• N192266190: Addresses an engine control software issue on 2018 models that can set P0021 after an auto stop/start event; corrected by an ECM reprogram.
• PIP5730B: Details a potential cause for P0021 from sticking Intake Camshaft Position Actuator Park Lock Solenoid Valves.
• Bulletin #N192266190 02: Notes that a software condition during a vehicle stop can cause the engine to run rough, stall, or set codes P0011, P0021, P0014, and P0024.
• Bulletin #PIP5568E: Communicates an ongoing investigation into cause and correction for the group of DTCs P0011, P0014, P0021, and P0024 setting together.

Platform-Specific Known Issues

• TSB N192266190: A GM Service Update for 2018 models addresses an ECM software issue causing P0021 and other cam codes after a stop/start event. The fix is an ECM reprogram.
• TSB PIP5730B: This bulletin points to sticking Intake Camshaft Position Actuator Park Lock Solenoids as a cause for P0021 on 2017-2019 models, a detail often missed in standard diagnostics.

Mechanic-Grade Diagnostic Values

• VVT Solenoid (Camshaft Actuator) Resistance — expected: 8 to 12 Ohms. Failure: A reading significantly outside this range, or an open/short (infinite or zero ohms), indicates a failed solenoid coil.
• Engine Oil Pressure at Idle (3.6L V6) — expected: Minimum 10 psi (69 kPa). Failure: Pressure below this minimum indicates a lubrication problem that can cause VVT system faults.
• Engine Oil Pressure at 2,000 RPM (3.6L V6) — expected: Minimum 20 psi (138 kPa). Failure: Pressure below this minimum points to a potential oil pump or internal engine issue.

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System): Camshaft Position Actuator Solenoid Test — This bidirectional control allows a technician to command the solenoid on and off while monitoring the desired vs. actual camshaft position angles on live data. If the actual angle does not change when the solenoid is commanded, it provides a definitive confirmation of a failure in the solenoid, its wiring, or the hydraulic circuit (phaser/oil pressure), ruling out an ECM logic issue.

Wiring & Ground Locations

• G105 / G106 — Located at the left front of the engine compartment and on the front center of the frame cross rail, under the crank pulley.. These are primary engine and chassis grounds. G101, which is connected to G106, specifically grounds the Engine Control Module (ECM). A loose or corroded connection here can cause erratic voltage and false codes from ECM-controlled components like the VVT solenoids.
• Bank 2 Intake VVT Solenoid Connector — On the front (radiator side) cylinder head, it is the upper of the two VVT solenoid connectors.. This is the direct connection point for the actuator. The two wires are typically Tan and Brown. Testing for voltage, ground, and resistance occurs at this connector.

Real Owner Repair Stories

• Reddit user with related GM engine (2017 Chevrolet Camaro with 3.6L LGX engine) — Check engine light with codes P0011 and P0021.
  ❌ Tried (didn't work) Initial diagnosis pointed towards potential solenoid or sensor failure.
  ✅ What actually fixed it The user reported the engine oil was dirty and sludgy. Performing a complete engine oil and filter change resolved both trouble codes.

OEM Part Supersession History

• 12655420, 12628347, 12646783, 12578517 → 12679099 — Standard part evolution for improved reliability and manufacturing.
  Heads up: The part number 12679099 is listed for the 2.4L engine in many parts catalogs, but is also confirmed by mechanics and forum users to be the correct, identical part for all four VVT solenoids on the 3.6L LGX.

Model Year Variations Within This Range

• 2018: This model year is specifically called out in GM Service Update N192266190 for an ECM software glitch that can falsely set P0021 and other timing codes after an engine auto stop/start event. The fix is a dealer-performed ECM reprogram.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• 8-Speed Automatic Transmission Shudder 🟠 Medium — A widely reported issue where the transmission causes a vibration or 'rumble strip' feeling, typically at light throttle between 35-55 MPH. It is often related to the original transmission fluid absorbing moisture. (Ref: TSB 18-NA-355 (recommends a fluid flush with an updated Mobil 1 Synthetic LV ATF HP fluid) and TSB 16-NA-019 address this issue for many GM 8-speed transmissions.)
• Harsh Shifting or Clunking from Transmission 🟠 Medium — Some owners report harsh 1-2 upshifts or hard 2-1 downshifts when coming to a stop. This is a separate issue from the fluid-related shudder and may point to internal valve body wear. (Ref: TSB 19-NA-266 discusses internal valve body repairs for this condition on some GM 8-speeds.)
• Start/Stop Accumulator Bolt Failure 🔴 High — A recall (N182198000) was issued for some 2018-2019 models because bolts on the transmission's start/stop accumulator endcap may be missing, which can lead to a transmission fluid leak, loss of propulsion, and fire risk. (Ref: Recall N182198000)
• Minor Electrical Gremlins 🟡 Low — A number of owners have reported intermittent issues with power windows, door locks, and the infotainment system.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used VVT solenoid is generally not recommended due to the risk of inheriting sludge, internal wear, or electrical faults. It should only be considered if it's from a verified, very low-mileage donor vehicle and can be tested for resistance before purchase.

Donor-vehicle mileage cap: roughly under 30000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• Inspect the solenoid's mesh screens; they should be perfectly clean and free of any metallic debris or sludge.
• If possible, test the resistance with a multimeter. It should be within the 8-12 Ohm specification.
• Ensure the electrical connector is not cracked, corroded, or full of oil.

OEM-only on this vehicle (don't cheap out):

• Camshaft Position Actuator Solenoid (VVT Solenoid)

Aftermarket brands forum-validated for this vehicle:

• ACDelco (GM Original Equipment)
• GM Genuine Parts
• Delphi (often the OEM manufacturer for GM)

Brands owners have reported issues with on this vehicle:

• Unnamed, no-brand solenoids from online marketplaces are a significant risk and frequently fail prematurely, leading to the code returning.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0011 — The Bank 1 equivalent of P0021; often sets alongside it if the root cause is dirty oil or the software glitch mentioned in N192266190.
• P0024 — Exhaust Camshaft Position Timing - Over-Advanced (Bank 2); this code will appear if you swap the faulty intake solenoid with the exhaust solenoid during diagnosis.
• P0014 — Exhaust Camshaft Position Timing - Over-Advanced (Bank 1); frequently sets with P0021 during auto-start events on 2018 models due to ECM software issues.
• P0106 — Manifold Absolute Pressure (MAP) sensor code; has been observed to trigger alongside P0021 on LGX engines during timing-related failures.

Frequently Asked Questions