2014-2020 Acura RLX 3.5L Hybrid J-Series: Problems, Identification, and Used Replacement

Part Identification: Is This Your Engine?

This article covers the JNB1 engine, a specialized 3.5L direct-injection V6 from the Honda J-Series family. It was designed exclusively for the 2014–2020 Acura RLX Sport Hybrid SH-AWD. This is not the same engine as the one in the front-wheel-drive (FWD) RLX.

Key features of the JNB1 engine include:

Common Failure Symptoms

Engine failure can be sudden, but some symptoms may give you a warning. Look out for:

• Abnormal Engine Noise: A persistent knocking or tapping sound from the engine, especially when warm, can indicate severe internal wear, such as connecting rod bearing failure.
• Engine Stalling: The engine may stall while driving, which could be caused by a failed timing belt or a problem with the fuel system. A complete failure of the timing belt will cause the engine to stop suddenly and not restart.
• Decreased Performance: A noticeable loss of power or hesitation during acceleration can be a sign of internal engine problems.
• Multiple Dashboard Warnings: While many issues can trigger warning lights, a combination of alerts accompanied by strange engine noises or performance loss often points to a serious engine fault. However, sometimes a weak 12-volt battery can cause numerous unrelated warnings, so it's wise to check the battery first.

Diagnostic Flowchart

Known Issues, Recalls, and Service Bulletins

Several documented issues affect this engine and its related systems. Always check with an Acura dealer to see if your specific vehicle is covered under any open recalls.

Connecting Rod Bearing Failure (Investigation)

A major recall (NHTSA 23V-751) was issued for connecting rod bearing failure in many Honda 3.5L V6 engines due to a crankshaft manufacturing defect. While the RLX was not officially included in this recall, the underlying J-series engine architecture is similar. The defect causes the connecting rod bearing to wear prematurely and seize, which can destroy the engine and increase the risk of a crash or fire. NHTSA continues to investigate failures in vehicles not covered by the initial recall.

Timing Belt Teeth Separation (Recall)

NHTSA Recall 19V-298 (Acura Recall Z4L) affects certain 2018–2019 Acura RLX Sport Hybrid models. Due to a manufacturing error, the teeth on the timing belt can separate from the belt itself. This can cause the engine's timing to slip, leading to a stall while driving and potentially catastrophic engine damage. Dealers will inspect the timing belt's lot number and replace it for free if it is part of the defective batch.

Fuel Pump Module Failure (Recall)

NHTSA Recalls 23V-858 and 20V-314 (Acura Recalls KGC, KGD, and 20-029) affect 2018–2020 models. The low-pressure fuel pump module inside the fuel tank can fail, leading to engine stalling or a no-start condition. The remedy is to replace the fuel pump module.

High Pressure Fuel Pump Chirp (TSB)

Acura Service Bulletin 16-008 applies to all years. Owners may notice a chirping sound from the engine area after it has warmed up. Acura states this noise comes from the high-pressure direct-injection fuel pump and is often a normal operating characteristic. Inspect the pump if the noise is excessive.

Timing Belt Chirp (TSB)

Acura Service Bulletin 14-025 covers all years. A different chirping noise, also heard when the engine is warm, may be caused by the timing belt rubbing against the crankshaft pulley. The corrective action is to adjust or replace the drive pulley shim to improve alignment.

Weak 12V Battery Causing Electrical Issues

A recurring minor issue across all years is the premature failure of the 12V auxiliary battery. A weak battery can cause a cascade of electrical warnings on the dashboard, which can easily be misdiagnosed as a major hybrid system or engine failure. Replacing the 12V battery often resolves these cascading lights.

Replacement Cost Estimates

Replacing the JNB1 engine is a significant expense. Costs vary based on the part source and local labor rates. The complex hybrid system makes installation more labor-intensive than a conventional engine swap.

What Fails at Every Mileage Band

Under 60,000 Miles

Engines in this range are relatively fresh, but failures still happen. Connecting rod bearing failure is less common here but has been reported as early as 61,000 miles. You may also encounter fuel pump module failures (covered by recall) and weak 12V batteries causing electrical gremlins.

• ✓Do during install (required): All required consumables (0W-20 full synthetic oil, filter, Honda/Acura Type 2 Blue pre-mixed coolant, intake/exhaust/thermostat gaskets).
• ✓Do during install (recommended): Inspect timing belt condition; while not due by mileage, age can be a factor (7-year interval).
• ✓Cheap insurance while the engine is out: New Spark Plugs (6 new OE-spec iridium), New 12V Auxiliary Battery (as a preventative measure).

60,000 - 100,000 Miles

This mileage range appears to be a critical window for severe connecting rod bearing failure. Multiple owner reports document catastrophic engine failure due to thrown rods or bearing seizure in this band. Additionally, many vehicles will reach the 7-year time limit for timing belt replacement regardless of mileage.

• ✓Do during install (required): Complete Timing Belt Kit (timing belt, hydraulic tensioner, idler pulley, adjuster pulley, water pump). This is non-negotiable in this mileage band. All required consumables (oil, filter, coolant, gaskets, rear main seal).
• ✓Do during install (recommended): New Spark Plugs and Valve Clearance Adjustment.
• ✓Cheap insurance while the engine is out: Inspect active engine mounts for any fluid leaks.

100,000 - 150,000 Miles

Connecting rod bearing failures continue to be reported in this higher mileage range. Furthermore, if the recommended 105,000-mile timing belt service is skipped, the risk of the original belt failing becomes extremely high, which will cause catastrophic interference engine damage.

• ✓Do during install (required): Complete Timing Belt Kit with Water Pump (assume it is due if history is unknown). All required consumables, including all major seals like front and rear main seals.
• ✓Do during install (recommended): New Spark Plugs and Valve Clearance Adjustment. Full inspection of all cooling system hoses and accessory belts.
• ✓Cheap insurance while the engine is out: Consider replacement of engine mounts, as they are likely worn.

Over 150,000 Miles

With meticulous maintenance, the JNB1 engine can exceed 200,000 miles. However, the well-documented connecting rod bearing issue presents a significant risk that can occur at almost any mileage. At this stage, failures are also likely to be related to the natural end-of-life for components like sensors, alternators, or starters.

• ✓Do during install (required): Complete Timing Belt Kit with Water Pump, all seals, spark plugs, and valve adjustment. Assume all major service items are due unless there is verifiable proof of recent replacement.
• ✓Do during install (recommended): Replace all accessory belts, tensioners, and coolant hoses.
• ✓Cheap insurance while the engine is out: Thoroughly inspect or replace high-wear items like the starter motor and alternator while the engine is out for easier access.

Real Owner Experiences

The following table highlights real-world failures and costs reported by Acura RLX Sport Hybrid owners.

Repair or Replace?

Deciding whether to repair your existing engine or replace it with a used unit depends entirely on the failure mode.

When to Repair: Minor issues like oil leaks from the valve cover gaskets or oil pan gasket typically cost $300 to $1,000 to fix and should always be repaired. If your vehicle experiences timing belt teeth separation and is covered under Recall 19V-298, the repair is free. If it is not covered, a timing belt replacement runs $800 to $1,500. Repair only makes sense if the timing belt failure did not cause internal engine damage (like bent valves or piston damage).

When to Replace: Replacement is the smartest path for any failure involving internal hard parts, most notably connecting rod bearing failure. Once metal shavings from a failed bearing circulate through the engine, they damage the crankshaft, camshaft journals, and oil passages. A simple bearing replacement is insufficient and unreliable. Given the massive 12 to 25 hours of labor required to remove the engine, attempting a partial rebuild is financially risky. Swapping in a complete used OEM engine (which typically runs $2,800 to $5,200) is a much more durable and cost-effective solution.

Freight, Delivery, and Pre-Purchase Verification

Buying a used engine means dealing with heavy freight. A complete JNB1 engine assembly weighs approximately 450 lbs and measures roughly 48" x 40" x 36" before crating. Because of this size and weight, it ships as LTL (Less Than Truckload) freight on a wooden pallet—it will NOT arrive via standard parcel delivery.

If you are having the engine shipped to a residential address or a shop without a loading dock or forklift, you must request a truck with a liftgate to lower the pallet to the ground. Always inspect the engine thoroughly for transit damage before signing the delivery receipt.

Installation Gotchas & Questions for Your Installer

Installing the JNB1 is an "Expert" level job requiring specialized tools like a Heavy-Duty Subframe Adapter/Cradle, an Engine Hoist/Crane with a Load Leveler, a specialized crankshaft pulley holder tool, and High-Voltage Safety Equipment (1,000V insulated gloves, safety glasses, insulated tools).

Installation Gotchas:

• Warning: You must disable the high-voltage hybrid system by pulling the High-Voltage Service Plug behind the rear seatback and waiting 10 minutes before starting work. Failing to do this can blow expensive high-voltage fuses or cause severe injury.

• Dual Cooling Loops: The vehicle has separate cooling systems for the engine and the hybrid inverter. Both must be bled. The inverter loop requires a Honda/Acura Diagnostic Scan Tool (HDS) command to run the electric water pump. Not bleeding this loop leads to air pockets, causing the hybrid system to overheat and enter limp mode.
• Subframe Drop: Standard procedure requires dropping the engine and transmission together from the bottom of the vehicle.
• Active Engine Mounts (ACM): These electronically controlled, fluid-filled mounts are fragile and expensive; handle them with care.
• Crankshaft Pulley Bolt: This bolt is extremely tight and requires a special heavy-duty holder tool and a high-torque impact wrench to remove.

• Warning: The JNB1 takes exactly 4.5 quarts of 0W-20 full synthetic oil with a filter change. Overfilling causes foaming, oil starvation, and spun rod bearings.

• Reusing the Rear Main Seal: Skipping replacement during install leads to expensive labor costs if it leaks later.

Questions to Ask Your Installer:

• Are you experienced with the Acura RLX Sport Hybrid platform and its high-voltage systems?
• Do you have the necessary high-voltage safety equipment?
• Will you be reusing my original engine wiring harness to ensure compatibility?
• Do you have the Honda HDS scan tool required to bleed the inverter cooling loop and perform the crankshaft position (CKP) pattern relearn?
• What new seals and gaskets will be replaced as part of the installation?
• How will you handle the immobilizer system? Will it require reprogramming at a dealership?

Before the First Start: Priming and Fluids

A used engine sits on a shelf for months. The oil drains away from the moving parts. If you start it dry, the metal parts will rub together and cause instant damage. You must prime (pre-lube) the engine to pump oil through the system before the engine actually runs.

Mandatory Fresh Fluids

Never reuse old fluids. Before priming, fill the engine with the correct, brand-new fluids:

• Engine Oil: Use fresh 0W-20 full synthetic motor oil. Install a brand-new oil filter.
• Engine Coolant: Use Honda/Acura Long Life Antifreeze/Coolant Type 2. This is a blue, 50/50 pre-mixed fluid. Do not mix it with green or orange coolants.

Oil Priming Procedure

Follow these steps to safely build oil pressure:

1. Disable the fuel system: Remove the fuel pump fuse from the fuse box. This stops fuel from spraying into the engine so it will not start.
2. Crank the engine: Turn the key or press the start button to crank the engine for 10 to 15 seconds.
3. Wait and repeat: Let the starter motor rest for 30 seconds so it does not overheat. Crank the engine again for another 10 to 15 seconds.
4. Watch the oil light: Repeat this process until the red oil pressure warning light on the dashboard turns off. This means oil has reached the top of the engine.
5. Start the engine: Put the fuel pump fuse back in place. Start the engine normally and listen for any strange noises.

Frequently Asked Questions (FAQ)