2018-2021 Honda Clarity PHEV 1.5L Engine: Failure Symptoms and Replacement Guide
This guide covers the common failure points, known issues, and replacement costs for the 1.5L gasoline engine in the 2018-2021 Honda Clarity Plug-in Hybrid.
- This engine ONLY fits the 2018-2021 Honda Clarity Plug-in Hybrid (PHEV). The 6th digit of the VIN must be '5' to ensure compatibility.
- The most common serious complaint is a sudden loss of power accompanied by loud, high engine revving, which is a significant safety concern.
- A major recall (NHTSA 23V-858) exists for the fuel pump on 2018-2019 models, which can cause the engine to stall. Ensure this has been addressed.
- Replacing the engine is a complex, high-voltage job not suitable for DIY. However, using a low-mileage used engine can make the repair economically viable compared to the cost of a new vehicle.
Symptoms of Failure
While the 1.5L engine in the Clarity PHEV is generally reliable, failures can occur. A failing engine may present several distinct symptoms. Some issues are related to the engine itself, while others stem from the complex hybrid powertrain control system.
1. Sudden Loss of Power with High Engine Revs
The most widely reported complaint involves the vehicle suddenly losing power and slowing to a crawl, while the gasoline engine revs loudly and erratically. This dangerous situation often occurs on the highway when the battery's charge is low and the car is transitioning to rely on the gas engine. Drivers report that the car fails to accelerate, and the engine noise is alarming. This issue has been noted in numerous NHTSA complaints and forum discussions, particularly in colder weather.
2. Flashing Check Engine Light
A flashing Check Engine Light is a universal sign of a serious problem. In the Clarity, it often indicates a severe engine misfire. When this happens, unburned fuel can be dumped into the exhaust system, which can quickly overheat and destroy the catalytic converter, leading to a very expensive repair. If the Check Engine Light is flashing, you should not drive the vehicle.
3. Catastrophic Internal Failure
In rare cases, a complete internal engine failure can occur. One owner reported a failure related to the rocker arm actuator system (DTC P2646), which led to "severe internal engine damage" requiring a full engine replacement. Symptoms of this level of failure include loud knocking or banging noises, excessive smoke from the exhaust, and metal shavings found in the engine oil during an oil change.
4. Check Engine Light with VTC-related Codes
Honda issued Technical Service Bulletin (TSB) #A18-079 for the check engine light coming on with DTC P100C (electric VTC motor speed signal circuit malfunction) and/or P0010 (variable valve timing control [VTC] malfunction). Another TSB, #A18-090, addresses software issues that can cause these same codes. These point to problems in the engine's variable timing control system, which is critical for efficiency and performance.
Compatibility Warning: This 1.5L engine assembly is ONLY for the Honda Clarity Plug-in Hybrid (PHEV) models from 2018-2021. It will not fit the all-electric (BEV) or fuel-cell (FCEV) versions. To confirm fitment, the 6th digit of your vehicle's VIN must be '5'. Verify this before purchasing.
Buying a Used 2018-2021 Clarity PHEV Engine
Purchasing a used engine can save you thousands of dollars compared to a new one, but careful inspection is key. Since this is a modern, complex hybrid powertrain component, you need to be extra diligent.
What to Inspect Before You Buy
- Verify the Part Number and VIN: Confirm the engine is from a 2018-2021 Clarity PHEV. The primary OEM part number for the engine block assembly is 10002-5WJ-A01 (or newer revisions like 10002-5WJ-A03), often paired with the cylinder head assembly 10003-5WJ-A00. Ask the seller for the VIN of the donor car to verify the 6th digit is '5'.
- Check for Physical Damage: Inspect the aluminum block and head for any cracks, especially around the mounting points. Look for signs of extreme overheating, such as warped plastic components or discolored metal.
- Ask About Mileage and Warranty: Reputable sellers will provide the mileage of the donor vehicle and offer a warranty. Given the car's value, an engine with under 100,000 miles and at least a 90-day warranty is recommended.
- Inspect for Oil Sludge: If possible, look under the oil filler cap. Thick, black sludge is a major red flag indicating poor maintenance and potential internal damage.
- Understand What's Included: Most used engines are sold as a "long block." This typically means the engine block and cylinder head are included, but accessories like the intake manifold, fuel injectors, wiring harness, and starter motor are not. You will need to transfer these parts from your old engine.
Pro Tip: Ask the seller if they can provide compression test numbers for the engine. A healthy engine will have strong and consistent compression across all cylinders. While not always possible, this data provides excellent insight into the engine's internal condition.
Known Issues, TSBs, and Recalls
While the engine itself is fairly robust, the Clarity PHEV has some known issues related to its powertrain and electronics.
- NHTSA Recall 23V-858 (Fuel Pump Failure): A major recall was issued for a wide range of Honda vehicles, including the 2018-2019 Clarity PHEV. The fuel pump inside the fuel tank may fail, causing the engine to stall while driving, which increases the risk of a crash. Dealers will replace the fuel pump module free of charge.
- TSB 21-008 (Hybrid System Failure): This bulletin addresses a symptom where the "Hybrid System Failure" message appears and DTC P1D8D (Generator Motor Inverter Short) is stored. The cause is an internal failure of the Power Control Unit (PCU), not the engine itself. The fix is a complete replacement of the PCU.
- TSB A18-079 & A18-090 (VTC Malfunction): These bulletins relate to software and circuit issues causing DTCs P100C and P0010, related to the engine's variable valve timing control system.
Cost to Replace the Engine
Replacing the engine in a Honda Clarity PHEV is a significant and expensive repair. A dealership was quoted charging $15,000 for the job ($11,000 in parts and $4,000 in labor). Opting for a used engine can dramatically lower the parts cost.
| Part/Service | Estimated Cost |
|---|---|
| New OEM Engine Assembly | $5,700 - $6,600+ (Part only) |
| Used OEM Engine Assembly | $300 - $1,000 (Part only, depending on mileage) |
| Independent Shop Labor | $1,500 - $2,500+ |
| Total (with Used Engine) | $1,800 - $3,500+ |
Frequently Asked Questions (FAQ)
Is it difficult to replace a Clarity PHEV engine?
Yes, this is a very difficult job rated 5 out of 5. It is not recommended for DIY mechanics. The procedure involves disconnecting high-voltage electrical systems, draining multiple fluids, removing the front subframe and axles, and requires an engine hoist and specialized tools. This job should be left to professional technicians experienced with hybrid vehicles.
Why does the engine rev so loudly in the Clarity?
The engine's primary job is to act as a generator to create electricity. The car's computer determines the most efficient RPM to run the engine for power generation, which doesn't always match the vehicle's speed. This can lead to the engine revving high even at a constant speed, which many drivers find unusual. However, if this is paired with a sudden loss of power, it indicates a serious problem.
Can I use an engine from a different Honda model, like an Accord Hybrid?
No. The engine and its integration with the hybrid system are specific to the Clarity PHEV. You must use an engine from another 2018-2021 Clarity PHEV. Using an engine from another model will result in compatibility issues with the wiring, computer systems, and transmission.
Is an engine replacement worth it on a 2018-2021 Clarity?
This depends on the vehicle's overall condition and value. In 2026, a used 2018 Clarity's value can range from about $10,000 to $13,000. If the rest of the car is in excellent shape and the repair can be done with a used engine for under $4,000, it may be a worthwhile investment compared to the cost of a replacement vehicle. However, if a dealership quotes over $10,000 for the repair, it may exceed the car's value.
Technical Specifications
OEM Part Numbers: 10002-5WJ-A01 10002-5WJ-A02 10002-5WJ-A03 10003-5WJ-A00
Engine Type: 1.5L Atkinson-Cycle 4-Cylinder. Primary Function: Electricity generation for the i-MMD hybrid system. Direct Drive: Engages only at sustained highway speeds.
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Honda Clarity:
- Symptoms of Failure
- 1. Sudden Loss of Power with High Engine Revs
- 2. Flashing Check Engine Light
- 3. Catastrophic Internal Failure
- 4. Check Engine Light with VTC-related Codes
- Buying a Used 2018-2021 Clarity PHEV Engine
- What to Inspect Before You Buy
- Known Issues, TSBs, and Recalls
- Cost to Replace the Engine
- Frequently Asked Questions (FAQ)
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