P0021 on 2017-2019 Cadillac XT5 3.6L: Software Glitches, Solenoid Failure, and Fixes

What's Unique About the 2017-2019 Cadillac XT5

For this specific XT5 with the 3.6L LGX engine, the P0021 code is uniquely tied to the vehicle's software, particularly concerning the auto stop/start system. General Motors issued a specific service update (N192266190) because a software glitch can cause the engine to run rough, stall, or set P0021 and other related timing codes immediately after an auto-start event. This makes it critical to check the vehicle's service history for this ECM reprogram before assuming a mechanical part has failed. The LGX engine uses 'mid-park' cam phasers to facilitate smoother restarts, and a glitch in the control logic for this system is the root of the software-related P0021 code. Manufacturer TSB Bulletin #N192266190 02 further clarifies that this condition can cause the engine to run at reduced power or stall while the vehicle is stopped.

Symptoms You May Notice

• Check Engine Light illuminated
• Engine runs rough or has an unstable idle
• Engine may stall, especially after an auto-stop/start event
• Reduced engine power and hesitation during acceleration
• Poor fuel economy
• Hard starting in some instances
• Rattling or knocking noises from the engine (indicates a more severe issue like timing chain problems or very low oil)

Most Likely Causes

1. Engine Control Module (ECM) Software Anomaly 🔴 High Probability → Shop Engine Control Module (ECM) A documented glitch in the ECM logic related to the auto stop/start feature can cause incorrect camshaft position readings after an engine restart. This is the subject of GM Service Update N192266190. The software anomaly prevents the 'verify sync' status from completing properly after an auto-start. Manufacturer TSB Bulletin #N192266190 notes that this specific software-related auto-start event is a primary cause for drivability concerns and rough running.
   How to confirm: Check with a GM dealer if Service Update N192266190 is open for your vehicle's VIN. The issue often presents with multiple timing codes (P0011, P0014, P0024) setting at once as history codes.
   Typical fix: A GM dealer will reprogram the Engine Control Module (ECM) with updated software. No parts are required for this fix, and it is performed under warranty or as a service campaign.
   Est. part cost: $0
2. Low or Dirty Engine Oil 🟡 Medium Probability The camshaft phasing system (VVT) is hydraulically operated by engine oil. The LGX engine can consume oil, and if the level is low, or the oil is dirty and sludgy, it cannot supply the proper pressure to operate the actuators correctly, causing them to stick or respond slowly.
   How to confirm: Check the engine oil dipstick. The oil should be within the correct range and not appear excessively dark, thick, or gritty. A Reddit user with a 2017 Camaro (same LGX engine) reported that dirty, sludgy oil triggered both P0011 and P0021, and an oil change resolved the codes.
   Typical fix: Perform an oil and filter change using a full synthetic 5W-30 oil that meets GM's dexos1 specification. Regular oil changes every 5,000 miles are recommended to prevent sludge buildup.
   Est. part cost: $50-$90
3. Faulty Intake Camshaft Position Actuator Solenoid (Bank 2) 🟡 Medium Probability → Shop Engine Camshaft This solenoid (also called a VVT solenoid or oil control valve) controls oil flow to the camshaft phaser. It can get clogged with debris from dirty oil or fail electrically, causing it to stick in the advanced position. It is a very common failure point on the 3.6L engine family.
   How to confirm: A technician can command the solenoid with a scan tool to check for response. A common DIY method is to swap the Bank 2 intake solenoid with the Bank 2 exhaust solenoid. Clear the codes and drive the vehicle. If the code changes to P0024 (Exhaust Cam Position Over-Advanced Bank 2), the solenoid is confirmed faulty. Resistance should measure between 6.9 and 7.9 ohms.
   Typical fix: Replace the Bank 2 intake camshaft position actuator solenoid. It is located on the front of the engine (radiator side) and is accessible after removing the engine cover. Apply clean engine oil to the new O-rings before installation. 🎬 Watch: Step-by-step VVT solenoid replacement for the 3.6L engine.
   Est. part cost: $40-$80

Rare But Worth Checking

• Sticking Intake Camshaft Position Actuator Park Lock Solenoid: → Shop Engine Camshaft Per GM TSB PIP5730B, the LGX engine has separate 'park lock' solenoids for the stop/start system. If the Bank 2 intake park lock solenoid sticks or comes apart, it can cause this code, sometimes without any other symptoms. This is a known issue that can be missed in normal diagnosis.
• Stretched Timing Chain: → Shop Engine Timing Chain While a major issue on the previous generation 3.6L (LLT/LFX) engines, it is less common on the LGX. However, with very high mileage or a history of poor oil maintenance (running with low oil), the chain can stretch enough to cause timing correlation errors. This is usually accompanied by rattling noises on startup.
• Clogged VVT Solenoid Oil Filter Screen: → Shop Engine Oil Filter Adapter In the cylinder head oil passage leading to the VVT solenoid, there is a small, thimble-shaped mesh filter. This screen can become clogged with sludge, especially if oil changes are neglected. This will starve the solenoid of oil pressure and can cause P0021 even after replacing the solenoid itself. The screen must be carefully removed and cleaned or replaced.

Diagnosis Steps

1. Scan the ECM for any other stored trouble codes. Note if P0011, P0014, or P0024 are present as history codes, as this points strongly to a software issue. Manufacturer TSB Bulletin #PIP5568B indicates that these codes often set together as part of a group.
2. Check the engine oil level and condition. If low, top it off. If the oil is dirty, sludgy, or past its service interval, perform a complete oil and filter change with GM-specified dexos1 Gen 2 (or newer) 5W-30 synthetic oil.
3. Contact a GM dealership with your VIN to determine if Service Update N192266190 is open or has been performed on your vehicle. If it has not been done, this is the most likely fix.
4. Inspect the wiring and connector for the Bank 2 (front bank) intake camshaft actuator solenoid for any signs of damage, corrosion, or loose connections.
5. If software and oil are good, test the solenoid. You can swap the intake and exhaust solenoids on Bank 2. Clear the codes and drive the vehicle. If the code changes to P0024, the solenoid you moved is faulty 🎬 See how to easily swap and fix VVT solenoids. and must be replaced.
6. If the solenoid is not the issue, consider inspecting the small filter screen in the oil passage leading to the solenoid for blockages.
7. If all else fails, a more advanced diagnosis may be needed to check for a faulty camshaft phaser or a sticking park lock solenoid (per TSB PIP5730B), which typically requires professional service.

Parts You'll Likely Need

• Intake Camshaft Position Actuator Solenoid (Bank 2) (OEM #12686594, superseding part number 12697123) — This is the most common mechanical part to fail that causes P0021. It gets stuck due to electrical failure or clogging from oil debris.
  Trusted brands: ACDelco, Delphi
  OEM price range: $50-$80
  Aftermarket price range: $35-$60
• Engine Oil and Filter — Incorrect, low, or dirty oil is a primary cause of VVT system faults. Using the correct oil is a critical first step in diagnosis and prevention.
  Trusted brands: ACDelco, Mobil 1, Pennzoil
  OEM price range: $60-$90
  Aftermarket price range: $50-$75
• Intake Camshaft Position Actuator Park Lock Solenoid Valve (OEM #12732244) — A less common but documented cause per TSB PIP5730B. This part can stick or break, causing timing codes without other symptoms.
  Trusted brands: ACDelco
  OEM price range: $40-$70
  Aftermarket price range: $30-$50

Related Codes That Often Appear With This One

• P0011 — Intake Camshaft Position Timing Over-Advanced for Bank 1. When seen with P0021, it strongly suggests the ECM software issue described in TSB N192266190 or a systemic oil pressure/level problem. Manufacturer TSB Bulletin #PIP5568E notes that this code may set in pairs with P0021 along with drivability concerns.
• P0014 — Exhaust Camshaft Position Timing Over-Advanced for Bank 1. The presence of multiple timing codes is a key indicator of the software glitch.
• P0024 — Exhaust Camshaft Position Timing Over-Advanced for Bank 2. If P0021 and P0024 appear together, it points to an issue affecting all of Bank 2, such as the software glitch or an oil flow problem to the front cylinder head.

Technical Service Bulletins (TSBs) & Recalls

• N192266190: Service Update for an engine control software issue
• PIP5730B: Diagnostic assistance for multiple timing codes (P0011, P0016, P0018, P0021) caused by sticking Intake Camshaft Position Actuator Park Lock Solenoids.
• Bulletin #N192266190 02: Specifies that dealers will reprogram the engine control module (ECM) to address rough running, reduced power, or stalling associated with DTCs P0011, P0021, P0014, and P0024.
• Bulletin #PIP5568E: Preliminary information regarding an investigation into the cause and correction for the group of DTCs (P0011, P0014, P0021, P0024) setting together or in pairs.

Platform-Specific Known Issues

• A known ECM software glitch can cause P0021 and other timing codes (P0011, P0014, P0024) to set, particularly after an auto stop/start event. This is covered by GM Service Update N192266190.
• The 3.6L LGX engine is sensitive to oil level and quality; running the engine even slightly low on oil can trigger multiple camshaft position codes simultaneously.

Mechanic-Grade Diagnostic Values

• Camshaft Position Actuator Solenoid Resistance — expected: 6.9 to 7.9 Ohms at 68°F (20°C).. Failure: A resistance reading outside this range, or an open/short circuit (OL or 0 ohms), indicates a faulty solenoid.
• Scan Tool Live Data: Desired vs. Actual Camshaft Position Angle — expected: The 'Actual' camshaft position angle should closely follow the 'Desired' angle commanded by the ECM within a few degrees as engine RPM and load change.. Failure: A large, persistent deviation between the desired and actual values, or an 'Actual' value that is stuck and does not change, points to a mechanical or hydraulic issue (solenoid, phaser, oil pressure).

Scan Tool Commands That Help

• GDS2 (GM Dealer Scan Tool): Camshaft Position Actuator Solenoid Control — Use this bidirectional command to manually activate the Bank 2 intake solenoid while monitoring engine response and scan tool data. This directly tests the solenoid's ability to function mechanically and electrically without removing it from the engine, helping to isolate a faulty solenoid from a wiring or oil pressure issue.
• GDS2 (or equivalent professional scan tool): Camshaft Position Relearn/Reset — After replacing a camshaft, phaser, or VVT solenoid, a relearn procedure may be required to reset the learned values in the ECM and ensure the system operates from a correct baseline.

Wiring & Ground Locations

• G101 — Located at the front of the engine, on the lower block area.. This is a primary ground for the Engine Control Module (ECM). A loose or corroded connection at G101 can cause a wide range of erratic sensor readings and seemingly unrelated engine codes, including timing faults. Before chasing complex component failures, verifying this ground is clean and tight is a crucial step.

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.
  ✅ What actually fixed it The user reported that the engine oil was dirty and sludgy. Performing a complete engine oil and filter change resolved both trouble codes.

OEM Part Supersession History

• 12686594 → 12697123 — Standard part revision and improvement by the manufacturer.
• Multiple (12647900, 12671336, 12680964, 12687167, 12690515, 12707054) → 12732244 — This is the part number for the 'Intake Camshaft Position Actuator Park Lock Solenoid Valve'. The extensive list of superseded numbers indicates multiple revisions over time to address failures.
  Heads up: When replacing a park lock solenoid, it is critical to use the latest part number (12732244) to ensure you have the most updated design.

Model Year Variations Within This Range

• 2017-2019: Within the 2017-2019 model years, the 3.6L LGX V6 engine and its VVT system components are consistent. No significant part or diagnostic changes related to code P0021 have been documented for this specific year range. Changes to engine options and oil specifications occurred in the 2020 and later model years.

Diagnostic Flowchart

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this specific repair, using used parts is not recommended. The primary mechanical failures are electronic solenoids, which are wear items. The cost savings from a junkyard part are minimal compared to the risk of premature failure and having to perform the labor again.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• If forced to use a used part, source from a vehicle with the lowest possible mileage.
• Avoid parts from vehicles that show signs of engine sludge in the oil fill cap.
• Ensure there is no physical damage to the part, especially the connector and O-rings.

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

• Camshaft Position Actuator Solenoid
• Camshaft Position Actuator Park Lock Solenoid Valve
• Camshaft Position Sensor

Aftermarket brands forum-validated for this vehicle:

• ACDelco (OEM)
• Delphi (Often an OEM supplier)

Brands owners have reported issues with on this vehicle:

• Dorman (for electronic components like solenoids, many mechanics report high failure rates).
• Unbranded parts from online marketplaces (e.g., Amazon, eBay), which often have poor quality control.

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 — This is the Bank 1 equivalent of P0021 ('A' Camshaft Position Timing Over-Advanced). It is frequently set alongside P0021 when the root cause is systemic, such as low engine oil or the ECM software glitch covered by TSB N192266190.
• P0024 — This code is for the Bank 2 Exhaust camshaft being over-advanced. It is a critical diagnostic companion to P0021, as swapping the intake and exhaust solenoids on Bank 2 will cause this code to appear if the intake solenoid was faulty.
• P0014 — This is the Bank 1 Exhaust camshaft equivalent of P0024. It often appears with P0011, P0021, and P0024 as a group when the cause is the ECM software anomaly or severe oil level/quality issues.
• P0018 — Crankshaft Position - Camshaft Position Correlation (Bank 2 Sensor A). This code is mentioned in TSB PIP5730B as a related timing code that can be caused by a sticking Intake Camshaft Position Actuator Park Lock Solenoid, a deeper mechanical issue related to the VVT system.
• P0016 — The Bank 1 equivalent of P0018. It indicates a correlation fault between the crank and cam sensors and can be triggered by the same advanced mechanical failures (like a sticking park lock solenoid) that might also cause P0021.

Frequently Asked Questions