2.5L eAssist SIDI DOHC Engine Complete Assembly for 2018-2019 Buick
Product Notes Read before buying
This is a 2.5L 4-cylinder engine (engine code LHN, VIN Z) with the eAssist mild hybrid system. It fits front-wheel drive models only. Please verify your vehicle has this exact engine before ordering.
Voice or type your vehicle details and Wrenchy will confirm fitment in seconds.
Vehicle Fitment Guide
This part fits the following vehicles:
| SubmodelSUB- MODEL |
Body Style | Years | Engine | Attributes |
|---|---|---|---|---|
| 2018 - 2019 |
Know This Engine Before You Buy
The research behind our purchase interview — recalls, bulletins and real install economics for this engine family:
A quick look at your own vehicle makes sure the right engine shows up:
- Verify the 8th Digit of your VIN is 'Z'
- Check the Engine Option Code (RPO) on the Service Parts Identification label for 'LHN'
- Confirm Drivetrain Configuration is Front-Wheel Drive (FWD)
- Look for thick, bright orange high-voltage cables routed to the starter-generator unit on the passenger side of the engine bay
What the install really takes — plan and budget with confidence:
Special tools this job needs:
- GM Belt Tensioner Compressor Tool (Kent-Moore EN-48932 or OTC 6725)
- High-Voltage Safety Equipment (Class 0 insulated safety gloves rated up to 1,000V)
- CAT III/IV digital multimeter
- GM-Compatible Diagnostic Scan Tool (GM GDS2 / Techline Connect / MDI 2)
- Engine Hoist / Lift
- Engine Stand
- Torque wrench
- Fuel line and A/C line disconnect tools
- Fuel injector seal installation and sizing tools
Budget for these consumables at install:
- Engine Oil: 5.0 quarts (4.7 liters) of 0W-20 full synthetic motor oil meeting GM dexos1 Gen 2 or Gen 3 specifications
- Oil Filter: Premium spin-on oil filter (such as ACDelco PF64 or equivalent)
- Coolant: GM-approved Dex-Cool (50/50 pre-diluted) for both primary and secondary MGU cooling loops
- Spark Plugs: 4 new iridium spark plugs (ACDelco 41-125 or equivalent), gapped to 0.95mm – 1.10mm (0.037" – 0.043")
- Gaskets: New intake manifold gasket, exhaust manifold gasket, thermostat gasket, and high-pressure fuel pump mounting O-ring/gasket
- Drive Belt: Brand-new, heavy-duty eAssist serpentine drive belt
What your vehicle’s computers will need after the swap:
What’s involved: Crankshaft Position (CKP) System Variation Learn & Immobilizer/Security Relearn
After installing the replacement engine, the ECM must calibrate itself to the new crankshaft's physical tolerances via a Crankshaft Position Variation Learn. If the ECM itself is replaced, a security/immobilizer relearn is also required to marry the new module to the BCM and ignition keys. A dealer-level scan tool (such as GM MDI/MDI 2 with GDS2) is required.
Pro tips for a smooth first start-up — hand them to whoever does the install:
- High-Voltage De-energization: Must physically disable the hybrid system by removing the High-Voltage Manual Service Disconnect (MSD) plug in the trunk and waiting 10 minutes before touching components.
- MGU Belt Tensioner Strut Orientation: The word 'TOP' must face up. Installing it upside down or reversing mounting bolts causes immediate belt misalignment, squeal, and belt shredding.
- Torque-to-Yield (TTY) Bolts: Cylinder head bolts, crankshaft balancer bolt, and connecting rod bolts are single-use and must be replaced.
- High-Pressure Fuel Pipe: The direct-injection fuel line running from the high-pressure pump to the fuel rail is a single-use crush-seal pipe and must be replaced.
- Fuel Injector Handling: Teflon seals must be replaced and properly sized using a special tool if transferring injectors to prevent fuel leaks.
Easy to get right once you know them:
- Ordering for a Non-Hybrid Vehicle: Attempting to install this engine in a standard, non-hybrid GM vehicle. The LHN engine is cast and machined specifically to accept the liquid-cooled eAssist MGU brackets.
- Buying the Wrong 2.5L Engine: Confusing the LHN with other GM 2.5L engines (like LCV or LKW) which have different mounting points and electronics.
- Reusing the High-Pressure Fuel Pipe: Reusing the original high-pressure fuel line which relies on a one-time crush seal, leading to fuel leaks.
- Upside-Down Tensioner Strut Installation: Reinstalling the eAssist belt tensioner strut upside down, leading to immediate belt failure.
- Blaming the Engine for Misfires Before Performing the Relearn: Skipping the mandatory Crankshaft Position Variation Learn procedure, which triggers misfire codes and a flashing Check Engine Light.
- Reusing Torque-to-Yield (TTY) Bolts: Reusing single-use TTY bolts for critical components.
Not issues with the units on this page — the manufacturer documented these for every engine of this family, wherever you buy one. Handy for your installer:
🔎 Recommended at install: Dealers will replace the high-pressure fuel pump and high-pressure fuel pipe free of charge.
🔎 Recommended at install: Dealers will inspect and replace the accumulator if bolts are missing.
🔎 Recommended at install: Requires a dual-stage ECM reprogramming procedure by a dealer.
🔎 Recommended at install: Replace the ECM.
🔎 Recommended at install: Inspect and replace the EVAP vent valve or update the ECM software.
🔎 Recommended at install: Follow diagnostic procedures to determine if internal parts can be repaired versus replacing the entire engine.
🔎 Recommended at install: Follow diagnostic and repair procedures outlined in the TSB.
Researched from factory recalls, TSBs and OEM service data (reference unit 300-10239-5506360). Unit-specific details — mileage, condition, warranty, freight — are covered in the checkout interview.
Policies, in plain English.
Shipping & Handling
- Ships by LTL freight on a pallet — a real freight truck, not a parcel van
- Your checkout freight quote covers delivery to your door (liftgate service included for residential addresses)
- The carrier calls ahead to schedule a delivery window — someone must be present to receive it
- Typically palletized and picked up within 2–3 business days; transit time depends on distance
120-Day Warranty
This part includes a 120-day warranty.
- If the part fails within the warranty window, we'll replace it or refund per the coverage terms
- Coverage is parts-only — installation labor is not included
- Warranty covers defects — not installation errors, misuse, or damage after installation
Your pre-purchase interview reviews these exact terms with you before anything is charged.
Returns (30 Days)
We accept returns of uninstalled parts within 30 days of delivery for this part.
- Defective parts: We will replace the part or issue a refund at our discretion
- Programming: "Needs to be programmed to my vehicle" is not a valid return reason. Many modules require dealer programming — we're happy to help connect you with resources if your dealer says it's not programmable
- Return shipping: This part ships by freight (LTL) — the part price is refundable per the terms above, but shipping costs are non-refundable and return freight follows the seller's return terms. Your pre-purchase interview walks through the exact numbers before you buy
- Parts must be returned in original packaging and unmodified condition
- Poorly packaged returns that arrive damaged will not be credited
Damaged in Shipping?
Freight damage is rare — and you're fully protected when you do two things at delivery:
- Inspect before you sign — you're allowed time to look the pallet over while the driver waits
- Write any damage on the delivery receipt before signing — that one line is what makes a freight claim succeed
- Severe damage? Refuse the delivery — it goes back at no cost to you and we make it right
- Photograph the pallet before unwrapping; report concealed damage within 24 hours of delivery
We handle the carrier claim — you just help document it. Your pre-purchase interview walks through this checklist too.
Order Cancellation
Cancel before shipment for a full refund. Once the pallet has been built, a preparation charge may apply — and once the freight carrier picks it up, shipping costs are non-refundable and standard return terms apply. Your pre-purchase interview shows the exact numbers before you pay.
Expert Guides
2018–2019 Buick LaCrosse 2.5L Ecotec: Problems, Identification, and Used Replacement
Identify the exact LHN eAssist engine, learn what causes it to fail, and discover when swapping in a used OEM unit is the smartest fix.
Read Full Guide →Related Trouble Codes (OBD-II)
5 matching guidesIf your scan tool is showing one of these trouble codes, this part is a common fix. Each guide explains the code, how to diagnose it, and exactly what to replace.
Miscellaneous Information
OEM Part Numbers:
Buick: 12681425
Fits Years: 2018 2019
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This unit ships with the selling yard's 120-day warranty. Longer plans can be requested during checkout.
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