P0333 on 2014-2017 Subaru Forester: Knock Sensor 2 Circuit High Causes and Fixes

What's Unique About the 2014-2017 Subaru FORESTER

The 2014-2017 Forester platform with the 2.5L naturally aspirated (NA) FB25 engine has a well-documented issue with this code. Subaru acknowledged that the original knock sensor (part #22060AA160) was prone to failure and issued a revised Technical Service Bulletin (TSB #07-133-18R). The official fix involves replacing the original sensor with a more durable version, part #22060AA180, which was originally designed for their turbo (DIT) engines and offers better resistance to heat and vibration.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Check Engine Light is on
• Reduced engine power and sluggish acceleration
• Noticeably decreased fuel economy
• Engine may hesitate or feel rough, especially under light load
• Audible engine pinging or knocking sound, especially under load (though sometimes there are no audible symptoms)

Most Likely Causes

1. Failing or Faulty Knock Sensor 🔴 High Probability Subaru issued TSB #07-133-18R acknowledging the original sensor on NA engines lacked durability due to heat and vibration. The plastic housing can crack, allowing moisture ingress and corrosion, leading to internal failure. This is the most common point of failure for this code.
   How to confirm: After checking wiring, the most practical test is to replace the sensor. You can also test the sensor's resistance with a multimeter (specification for a similar sensor is 530-580 kΩ, but always verify for the specific part) or swap the Bank 1 and Bank 2 sensors and see if the code follows to the other bank (e.g., P0328).
   Typical fix: Replace the Bank 2 knock sensor with the updated OEM part #22060AA180.
   Est. part cost: $45-$90
2. Damaged Wiring or Connector 🟡 Medium Probability The wiring harness is in the engine bay, exposed to heat and potential rodent damage. Rodents are known to chew on the soy-based wire insulation used in some modern cars. A short to voltage in the signal wire will cause a 'circuit high' code.
   How to confirm: Visually inspect the wiring harness leading to the Bank 2 knock sensor for any signs of cracking, melting, or rodent chews. Check the connector for corrosion, moisture, or bent/spread pins. Perform a continuity test from the sensor connector to the ECM.
   Typical fix: Repair the damaged section of wire or replace the connector pigtail.
   Est. part cost: $10-$30
3. Loose Knock Sensor ⚪ Low Probability Vibrations can potentially loosen the single mounting bolt over time if it wasn't torqued correctly during a previous repair. An improperly mounted sensor cannot 'hear' the engine correctly.
   How to confirm: Attempt to move the sensor by hand. Check the mounting bolt to see if it is torqued to the factory specification, which is 24 Nm / 17.7 ft-lbs. A loose sensor can cause false knock readings or circuit codes.
   Typical fix: Clean the mounting surface on the engine block and torque the knock sensor mounting bolt to the correct specification. Do NOT use anti-seize compound.
   Est. part cost: $0

Rare But Worth Checking

• Powertrain Control Module (PCM) Failure: This is very uncommon. Before condemning the PCM, all other possibilities, especially the sensor and wiring, must be exhaustively ruled out. A PCM failure is a last resort diagnosis.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0333 is present and check for any other codes.
2. Locate the Bank 2 knock sensor. On the 2.5L FB25 engine, it is on the rear of the engine block, on the driver's side (Bank 2 is the left side on a Subaru), somewhat buried near the firewall.
3. Visually inspect the sensor's electrical connector and nearby wiring for any obvious damage, corrosion, loose connections, or signs of rodents.
4. If wiring looks good, check that the sensor is securely bolted to the engine block. It should be torqued to 24 Nm (17.7 ft-lbs). A clawfoot or crow's foot socket may be helpful for access.
5. If accessible, disconnect the sensor and measure the resistance across its pins. Compare this to the manufacturer's specification. An open or shorted sensor is faulty.
6. The most definitive and common fix, as recommended by Subaru's TSB, is to replace the sensor with the updated part number (22060AA180).
7. After replacement, ensure the mounting surface is clean, torque the new sensor correctly, and clear the codes with the scanner. Perform a test drive to ensure the code does not return.

Parts You'll Likely Need

• Knock Sensor (OEM #22060AA180) — This is the updated, more durable part recommended by Subaru's TSB #07-133-18R to fix the root cause of the failure. It supersedes the original, failure-prone part #22060AA160.
  Trusted brands: Subaru (Genuine), Denso, NTK
  OEM price range: $45-$90
  Aftermarket price range: $25-$65

Related Codes That Often Appear With This One

• P0332 — This is the code for 'Knock Sensor 2 Circuit Low'. It can appear with P0333 if the wiring is intermittently shorting and opening, causing voltage to swing between extremes.
• P0327 / P0328 — These are the 'Circuit Low' and 'Circuit High' codes for Bank 1 (passenger side). Seeing them along with P0333 could indicate a systemic issue like a damaged shared harness, rodent damage affecting both sides, or a problem affecting both sensors.

Technical Service Bulletins (TSBs) & Recalls

• Bulletin #07-133-18R: This is a revised TSB that announces a design change, replacing the original knock sensor with a more durable one from the DIT (turbo) engines to address codes P0327, P0328, P0332, and P0333 on NA engines. It confirms the torque spec is 17.7 ft-lbs and warns against using anti-seize.

Platform-Specific Known Issues

• A known issue documented in Subaru TSB #07-133-18R describes how the original knock sensor on naturally aspirated engines can fail, triggering codes P0327, P0328, P0332, or P0333. The bulletin advises replacing it with a more durable sensor (originally for turbo models) to improve heat resistance.

Mechanic-Grade Diagnostic Values

• Knock Sensor Resistance — expected: > 400 kΩ (between sensor pin and metal housing). Failure: A reading of 0 ohms, a few ohms, or significantly below 400 kΩ indicates a faulty, shorted sensor. An open circuit (infinite resistance) also indicates failure.
• Harness Voltage (Key On, Engine Off) — expected: ~5V DC (measured at the harness connector with sensor unplugged). Failure: A reading of 0V indicates a wiring problem between the ECM and the connector. If the voltage is ~5V when unplugged but does not drop when the sensor is connected, the sensor is likely open internally.
🎬 See this guide on Subaru knock sensor diagnosis
• Sensor AC Voltage Output (Dynamic Test) — expected: > 1V AC (when tapping the engine block near the sensor). Failure: A very low reading (e.g., in the millivolt range) when tapping indicates the sensor's piezoelectric element is not generating a signal correctly and the sensor is bad.

Wiring & Ground Locations

• Knock Sensor Connector — On the rear of the engine block, driver's side (Bank 2), connected to the knock sensor.. This connector (wiring diagram ID R69 or E14) and its pigtail are exposed to extreme heat and vibration, making them a potential failure point for corrosion or wire fatigue, which can cause a P0333 code.
• ECU Ground — The primary ground reference for the ECU is established via the intake manifold, which is then grounded to the chassis.. A poor ground connection at the intake manifold can cause a variety of strange electrical issues and incorrect sensor readings. While not a direct cause of a single sensor circuit high code, ensuring this ground is clean and secure is a foundational step in any electrical diagnosis on a Subaru.

Real Owner Repair Stories

• IH8MUD.com Forum (Toyota (similar V-engine layout, principle applies)) — Check Engine Light with P0333.
  ❌ Tried (didn't work) Replacing both knock sensors.
  ✅ What actually fixed it The wiring harness pigtail for the Bank 2 knock sensor had failed. Replacing just the pigtail by soldering in a new one resolved the code permanently.

OEM Part Supersession History

• 22060AA160 → 22060AA180 (or 22060AA18A for US-built models) — The original sensor was prone to failure from heat and vibration. The new part, originally for turbo (DIT) engines, offers improved durability and heat resistance.

Model Year Variations Within This Range

• 2014-2016: Forester models built before November 18, 2016 (VIN HH538942) were factory-equipped with the original, less durable knock sensor (22060AA160) and are more likely to experience this failure.
• 2017: Later 2017 models built after November 18, 2016 (VIN HH538942 and later) were equipped from the factory with the more durable, updated knock sensor (22060AA18A), making this failure less common on these specific vehicles.