# 2020 Prius Prime Cranks But Won't Start: Crankshaft Sensor Fix

> ClearTheCode — Is your 2020 Toyota Prius Prime PHEV cranking but won't start? A faulty crankshaft position sensor is a common culprit. Learn to diagnose and fix this issue to restore your vehicle's reliability.

Source: https://clearthecode.com/articles/engine-crankshaft-position-sensor-failure-toyota-prius-prime-phev-2020
Code: P0335
Author: ClearTheCode

# Engine cranks but won't start due to crankshaft position sensor 2020 Toyota Prius Prime (Phev)

Few things are as frustrating as turning the key or pushing the start button in your 2020 Toyota Prius Prime PHEV, only to hear the engine crank vigorously without actually firing up. This common scenario often points to a critical component failure: the crankshaft position sensor. This sensor is vital for the engine's computer (ECU) to determine engine speed and piston position, information crucial for precise ignition timing and fuel delivery. When it fails, the ECU loses its reference, preventing the internal combustion engine (ICE) from starting, even though the starter motor is working perfectly.

## What drivers notice on this 2020 Toyota Prius Prime (Phev)

The primary symptom experienced by 2020 Prius Prime owners with a failing crankshaft position sensor is the engine cranking but not starting. This isn't a weak battery or a slow starter; the engine spins over at a normal speed, but it simply won't catch and run. You might also notice:

- The vehicle operating normally in EV mode, but failing to engage the ICE when needed.
- A complete inability to start the gasoline engine under any circumstances.
- The Check Engine Light (CEL) illuminating on the dashboard.
- Potentially, an extended cranking time before the engine finally starts, if the sensor is failing intermittently.

## At a glance: difficulty, repair cost, and diagnostic workflow

- **Difficulty Rating:** 6/10 — 6/10 — Intermediate diagnostics
- **Common Symptoms:** Engine cranks but does not start: The most common and direct symptom.; Intermittent stalling: The engine might suddenly shut off while driving, especially after warming up.; Rough idling or misfires: If the sensor provides erratic signals, the engine's timing can be disrupted.; Reduced power or acceleration: The ECU might enter a 'limp mode' to protect the engine if it receives unreliable data.
- **Estimated Repair Cost:** $120–$450 (parts + typical shop labor)
- **OEM Tooling Required:** Standard OBD-II scanner and hand tools

**Diagnostic workflow:**
1. Confirm P0335 with a live scan — note pending vs stored and freeze frame data.
2. Inspect wiring/connectors and related sensors before replacing modules.
3. Clear codes and road-test; re-scan after two drive cycles if the monitor must set.

See the [P0335 code reference](/codes/P0335) and [topic hub](/hubs/fuel-trim-air-metering) for related guides.

## Symptoms and warning signs

While the most definitive sign is a no-start condition, other symptoms can precede a complete failure:

- **Engine cranks but does not start:** The most common and direct symptom.
- **Intermittent stalling:** The engine might suddenly shut off while driving, especially after warming up.
- **Rough idling or misfires:** If the sensor provides erratic signals, the engine's timing can be disrupted.
- **Reduced power or acceleration:** The ECU might enter a 'limp mode' to protect the engine if it receives unreliable data.
- **Poor fuel economy:** Inaccurate timing can lead to inefficient combustion.
- **Check Engine Light (CEL):** The ECU will typically set a diagnostic trouble code (DTC) when it detects a problem with the crankshaft position sensor circuit.

## What is different on this year and model

The 2020 Toyota Prius Prime is a Plug-in Hybrid Electric Vehicle (PHEV), which means its operation differs significantly from a conventional gasoline car. When the crankshaft position sensor fails, the impact is specific to the internal combustion engine (ICE). The vehicle might still be able to operate in pure EV mode, powered solely by its electric motor and battery. However, once the system commands the ICE to start—either due to battery depletion, high speed, or driver demand—the engine will crank but not start. This can be confusing, as the car otherwise appears functional in EV mode. The hybrid system may also display specific warnings on the multi-information display indicating an engine system malfunction, even if the car can still move under electric power.

## How to verify and confirm the issue

Verifying a faulty crankshaft position sensor on your 2020 Prius Prime involves a combination of practical checks and diagnostic tools:

- **OBD-II Scan Tool:** Connect a diagnostic scanner to your vehicle's OBD-II port. Look for a Diagnostic Trouble Code (DTC) such as P0335, which specifically indicates a Crankshaft Position Sensor 'A' Circuit Malfunction. For more details on diagnostic trouble code P0335, see our [P0335 reference](/codes/P0335).
- **Live Data Monitoring:** With the scan tool connected, monitor the engine RPM reading while cranking the engine. A healthy crankshaft position sensor should show a consistent RPM signal (e.g., 100-200 RPM) during cranking. If the reading is 0 RPM or erratic, it strongly suggests a sensor or circuit issue.
- **Visual Inspection:** Carefully inspect the crankshaft position sensor itself and its wiring harness. Look for:
    - Frayed, cut, or damaged wires.
    - Corroded or bent pins within the electrical connector.
    - Loose connections at the sensor or along the harness.
    - Signs of rodent damage to the wiring.
- **Confirm Spark and Fuel:** While a bad crankshaft sensor is a strong suspect for a no-start, it's good practice to quickly confirm spark and fuel delivery. If the sensor is truly bad, the ECU won't command spark or fuel injection, so these will be absent. If spark and fuel are present, the problem lies elsewhere.
- **Check for TSBs:** Consult Toyota's Technical Service Bulletins (TSBs) for your specific 2020 Prius Prime model. There might be known issues or updated procedures related to the crankshaft position sensor.

## Common causes (most likely first)

Several factors can lead to a crankshaft position sensor failure in your Prius Prime:

- **Internal Sensor Failure:** Over time, the electronic components within the sensor can degrade due to heat, vibration, or manufacturing defects, leading to intermittent or complete failure. This is the most common cause.
- **Wiring Harness Damage:** The sensor's wiring can become brittle, frayed, or damaged due to exposure to engine heat, abrasion, or even rodent activity. This disrupts the signal path to the ECU.
- **Connector Corrosion or Looseness:** The electrical connector pins can corrode, preventing a good electrical connection, or the connector itself can become loose, leading to intermittent signal loss.
- **Reluctor Wheel Damage:** Less common, but physical damage to the reluctor wheel (the toothed wheel on the crankshaft that the sensor reads) can prevent the sensor from generating an accurate signal. This usually occurs during other engine work.
- **Heat Stress:** Constant exposure to high engine temperatures can accelerate the degradation of the sensor's internal components.

### Related guides on this vehicle

- [2020 Toyota Corolla: Car Won't Start, No Fuel Pump Prime Sound](/articles/car-wont-start-no-fuel-pump-prime-toyota-corolla-2020)
- [Engine Cranks But Won't Start No Fuel Pressure 2018 Toyota Rav4](/articles/engine-cranks-wont-start-no-fuel-pressure-toyota-rav4-2018)
- [2020 Toyota Highlander: Car Won't Start, No Crank, No Power At All](/articles/car-wont-start-no-crank-no-power-8772-toyota-highlander-2020)

## Step-by-step diagnosis and fixes

Addressing a faulty crankshaft position sensor typically involves diagnosis and replacement. Always prioritize safety when working on your vehicle, especially with a hybrid system.

1.  **Safety First:** Disconnect the 12V auxiliary battery's negative terminal to prevent accidental shorts or activation of high-voltage components. For hybrid vehicles, always consult the owner's manual for specific safety precautions.
2.  **Locate the Sensor:** The crankshaft position sensor on a 2020 Toyota Prius Prime is generally located near the crankshaft pulley at the front of the engine or on the engine block near the transmission bell housing. Its exact position can vary slightly, so consult a service manual for your specific model.
3.  **Inspect Wiring and Connector:** Before replacing, thoroughly inspect the sensor's electrical connector and the wiring harness leading to it. Look for any visible damage, corrosion, or loose connections. Repair any wiring issues found.
4.  **Confirm DTC:** Use an OBD-II scanner to confirm the presence of P0335. Clear the code and attempt to start the engine. If the code immediately returns, it reinforces the sensor or circuit issue.
5.  **Remove the Old Sensor:**
    - Disconnect the electrical connector from the sensor.
    - Use the appropriate socket or wrench to unbolt the sensor from its mounting point. Be careful not to drop the bolt or the sensor.
    - Gently pull the old sensor out. It might be snug due to an O-ring seal.
6.  **Install the New Sensor:**
    - Ensure the mounting surface is clean.
    - Apply a small amount of clean engine oil to the new sensor's O-ring (if present) to aid installation and proper sealing.
    - Insert the new sensor into its bore.
    - Reinstall and tighten the mounting bolt to the manufacturer's specified torque. Overtightening can damage the sensor or engine block.
    - Reconnect the electrical connector, ensuring it clicks securely into place.
7.  **Reconnect Battery and Test:** Reconnect the 12V battery's negative terminal. Clear any remaining diagnostic trouble codes with your scan tool. Attempt to start the engine. It should now start and run smoothly.
8.  **Verify Operation:** After starting, ensure the Check Engine Light remains off and the engine runs without any misfires or stalling. Take a short test drive to confirm normal operation.

## Repair options and cost factors

When facing a crankshaft position sensor failure, you have a couple of repair options:

-   **DIY Replacement:** If you're comfortable working on your vehicle and have basic tools, replacing the sensor yourself is the most cost-effective option. The primary cost will be the sensor part itself. OEM Toyota sensors are generally recommended for reliability, though quality aftermarket options exist. Prices for the sensor typically range from $50 to $150.
-   **Professional Repair:** Taking your 2020 Prius Prime to a qualified technician or Toyota dealership will incur labor costs in addition to the part cost. The labor time for this job is usually 1-2 hours, depending on the sensor's accessibility. Professional diagnosis ensures other potential issues are ruled out. For other repair guides, visit our All repair guides section.

## When to see a professional

While a DIY replacement is feasible for many, there are situations where consulting a professional is advisable:

-   **Uncertain Diagnosis:** If you've performed basic checks and are still unsure if the crankshaft position sensor is the sole problem, a professional can provide a definitive diagnosis.
-   **Difficult Access:** Some crankshaft position sensors can be challenging to reach, requiring specialized tools or removal of other components. If you lack the necessary tools or experience, professional help is best.
-   **Persistent Issues:** If the engine still won't start or runs poorly after replacing the sensor, there might be a deeper electrical issue or another component failure that requires advanced diagnostic equipment.
-   **Hybrid System Concerns:** Working on hybrid vehicles requires specific safety knowledge due to high-voltage components. If you're uncomfortable, always defer to a professional.

## Frequently asked questions

### Can a bad crankshaft sensor cause other problems in a 2020 Prius Prime?
Yes, beyond a no-start, an intermittently failing crankshaft position sensor can cause misfires, rough idling, reduced power, and poor fuel economy in your 2020 Prius Prime. The hybrid system might also limit power or prevent the internal combustion engine (ICE) operation, leading to unexpected driving behavior.

### How long does it take to replace a crankshaft position sensor on a 2020 Toyota Prius Prime?
For a professional technician, replacing a crankshaft position sensor on a 2020 Toyota Prius Prime typically takes between 1 to 2 hours, depending on the sensor's exact location and accessibility. A do-it-yourself enthusiast might take longer, especially if it's their first time performing this specific repair.

### Is it safe to drive my 2020 Prius Prime with a bad crankshaft position sensor?
No, if the crankshaft position sensor is completely faulty and preventing your engine from starting, your 2020 Prius Prime is undrivable. If it's intermittently failing and causing stalling or rough running, it is unsafe to drive as you could lose engine power unexpectedly, posing a significant safety risk.

## Sources and further reading

Always consult your 2020 Toyota Prius Prime's official factory service manual for precise diagnostic procedures, torque specifications, and component locations. For more details on diagnostic trouble code P0335, see our [P0335 reference](/codes/P0335). Explore more about engine management and [fuel trim and air metering](/hubs/fuel-trim-air-metering) issues. You can also [browse other vehicles](/vehicles) for common issues.

This article is intended for informational purposes and is not a substitute for OEM service procedures; always use a qualified technician for safety-critical work.

## Explore related guides on ClearTheCode

- [Browse OBD-II codes](/codes)
- All repair guides