P0325 on 2016-2020 Acura ILX: Knock Sensor Circuit Malfunction Causes and Fixes

What's Unique About the 2016-2020 Acura ILX

The 2016-2020 Acura ILX uses the reliable 2.4L K24W7 engine. For this engine family (Honda/Acura K-series), the P0325 code is a well-documented issue. A frequent and notable cause is rodents chewing through the knock sensor wiring harness, as the soy-based wire insulation used by Honda can attract them. The sensor itself is also located on the back of the engine block, under the intake manifold, making access labor-intensive for a DIY repair and providing a sheltered area for rodents to nest.

Symptoms You May Notice

• Check Engine Light is on
• Reduced engine power and sluggish acceleration
• Decreased fuel economy
• Engine hesitation
• Audible engine pinging or knocking noises (in some cases)

Most Likely Causes

1. Damaged Knock Sensor Wiring or Connector 🔴 High Probability → Shop Ignition Knock (Detonation) Sensor Honda/Acura has historically used soy-based wire insulation that can attract rodents, who then chew through the wiring. The location under the intake manifold provides a sheltered spot for this to happen. Forum users on AcuraZine and Reddit consistently report this as the number one cause for P0325 on various Acura models.
   How to confirm: Visually inspect the knock sensor wiring harness for signs of being chewed, frayed, or corroded. This requires removing the intake manifold to access the sensor, which is located on the engine block.
   Typical fix: Repair the damaged section of wiring or, more reliably, replace the knock sensor sub-harness. 🎬 Watch: How to easily repair damaged rodent wiring The OEM sub-harness is part number 32113-5G0-A00.
   Est. part cost: $30-$60 for an OEM sub-harness
2. Faulty Knock Sensor 🟡 Medium Probability → Shop Ignition Knock (Detonation) Sensor The sensor is exposed to constant heat cycles and vibrations, which can cause the internal piezoelectric element to fail over time.
   How to confirm: After confirming the wiring is intact, test the sensor's resistance with a multimeter against factory specifications. If the reading is out of spec or shows an open circuit, the sensor is bad. The sensor can also be tested for AC voltage output while tapping on the engine block near the sensor (with the engine off).
   Typical fix: Replace the knock sensor. It is critical to use an OEM or high-quality Denso replacement and torque it to the manufacturer's specification, typically around 20-24 Nm (15-18 ft-lbs). Over-torquing can make the sensor overly sensitive and cause it to throw codes, while under-torquing can prevent it from detecting real knock.
   Est. part cost: $150-$220 for an OEM sensor

Rare But Worth Checking

• Powertrain Control Module (PCM) Fault: → Shop Engine Control Module (ECM) This is very uncommon, but if the sensor and wiring have been tested and confirmed to be good, the PCM's internal circuit for the knock sensor could be the issue. This should be the last resort after all other possibilities are exhausted.
• Cooling System Malfunction: An overheating engine can cause actual engine knock, which might, in some fringe cases, cause issues with the sensor circuit or trigger related codes. Ensure the cooling system is functioning correctly.
• Persistent Engine Knock: In rare cases where the code appears after using low-quality fuel or if there is excessive carbon buildup, the sensor may be functioning correctly and reporting a real, persistent knock condition. A user on AcuraZine with an '04 TSX chased a P0325 code that persisted after replacing the sensor and harness, raising the possibility of a real knock condition being the trigger.

Diagnosis Steps

1. Scan the vehicle's computer for the P0325 code and any other stored codes.
2. Document the freeze frame data to understand the engine conditions when the code was set.
3. Gain access to the knock sensor by removing the upper intake manifold. This involves disconnecting the throttle body, various vacuum lines, and electrical connectors.
4. Perform a thorough visual inspection of the knock sensor, its connector, and the sub-harness leading to the main engine harness. Look for any signs of damage, especially from rodents.
5. If the wiring looks good, disconnect the sensor and test its internal resistance using a digital multimeter. Compare the reading to the manufacturer's specifications (if available). An open circuit indicates a failed sensor.
6. Check for the proper reference voltage (typically around 5V) and ground at the connector coming from the PCM to ensure the circuit is intact.
🎬 See this step-by-step knock sensor diagnostic guide
7. If the sensor and wiring are confirmed to be good, the issue may lie with the PCM, though this is rare.

Parts You'll Likely Need

• Knock Sensor (OEM #30530-R1A-A01) — The sensor itself can fail due to age and heat cycles, causing an incorrect signal to be sent to the PCM.
  Trusted brands: Genuine Acura/Honda, Denso
  OEM price range: $180-$220
  Aftermarket price range: $50-$120
• Knock Sensor Sub-Harness (OEM #32113-5G0-A00) — This is the most common failure point on many Honda/Acura vehicles due to rodents chewing the soy-based wires.
  Trusted brands: Genuine Acura/Honda
  OEM price range: $30-$60
  Aftermarket price range: $20-$40

Platform-Specific Known Issues

• Intake Manifold Removal Required: → Shop Engine Intake Manifold Unlike some vehicles where the knock sensor is easily accessible, on the K24W7 engine it is located beneath the intake manifold. This adds significant time and complexity to the repair, as the manifold, throttle body, and associated connections must be removed for access.

Mechanic-Grade Diagnostic Values

• Harness Connector Bias Voltage (Key On, Engine Off) — expected: Approximately 4.8-5.0V DC. Failure: Significantly lower or no voltage indicates a problem with the PCM or the wiring between the PCM and the sensor connector.
• Knock Sensor AC Voltage Output (Bench Test) — expected: Generates a small AC voltage when the engine block near it is tapped. A light tap might produce ~2.0V AC.. Failure: No voltage or an erratic signal when tapped indicates a failed internal piezoelectric element.
• Knock Sensor Internal Resistance — expected: Infinite resistance (Open circuit). There should be no continuity between the center pin and the sensor body (ground).. Failure: Any continuity reading indicates the sensor is internally shorted.

Wiring & Ground Locations

• Knock Sensor Signal Wire at PCM — The wire is typically Red with a Blue stripe (RED/BLU) leading to the Powertrain Control Module (PCM).. This is the primary wire that carries the knock signal. Technicians can test for continuity and shorts on this wire directly from the PCM connector to the sensor connector to isolate a wiring fault from a sensor or PCM fault.
• G101 — On many Honda/Acura platforms, G101 is a primary engine ground located on or near the thermostat housing.. The shielded wire for the knock sensor circuit requires a clean ground path to prevent signal interference from the ignition system. The braided shield wire often grounds at G101, and a poor connection here could potentially introduce noise and contribute to a P0325 code.

Real Owner Repair Stories

• YouTube channel 'blacklistedcrv' (Honda CR-V with K24 engine (similar architecture to the ILX's K24W7)) — Persistent P0325 code.
  ❌ Tried (didn't work) Replacing the knock sensor alone did not always fix the issue.
  ✅ What actually fixed it The sub-harness that runs the knock sensor wire alongside the starter signal wire failed internally. The permanent fix was to bypass the faulty sub-harness by running a new wire from a new sensor pigtail directly to the main engine harness connector, soldering and heat-shrinking the connection.
• Honda Accord Forum user 'tap500' (2001 Honda Accord 2.3L) — P0325 code after finding the original sensor had physically fallen apart.
  ❌ Tried (didn't work) Replacing the sensor with a cheap eBay part., Replacing the sensor again with a cheap Amazon part.
  ✅ What actually fixed it The discussion concluded that for Honda/Acura vehicles, using a non-OEM knock sensor is a very common reason for the P0325 code to persist even after replacement. The solution is to use a Genuine Honda/OEM sensor.

OEM Part Supersession History

• 30530-R1A-A01 → 30530-5PA-A01 — Standard part number update by the manufacturer.
  Heads up: The new part number is a direct replacement and is compatible.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Harsh Downshifts from 8-Speed DCT 🟠 Medium — Common on 2016-2017 models. A distinct 'bump' or 'lurch' when coming to a stop. (Ref: TSB 17-015 describes a PCM software update and clutch break-in procedure to fix the issue.)
• Brake Master Cylinder Leak 🔴 High — Affects all 2016-2020 models, leading to a recall. (Ref: NHTSA Recall 23V858000 (Honda recall RN5). Contaminated brake fluid can cause a seal to deform, leading to a fluid leak, reduced pedal firmness, and increased stopping distance.)
• Denso Fuel Pump Failure 🔴 High — Part of a massive Honda/Acura recall affecting many models, including the ILX. The fuel pump impeller can deform and fail, causing the engine to stall. (Ref: Part of a broad recall affecting over 708,000 Honda and Acura vehicles.)
• Steering Wheel Rattles or Clicks 🟡 Low — Some owners report various noises from the steering wheel area when turning. (Ref: TSB B16-025 addresses a creaking, rattling, or clicking noise from the driver's airbag area.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used OEM knock sensor sub-harness (pigtail) from a junkyard is a viable option if it is in excellent physical condition with no signs of brittleness, corrosion, or rodent damage. The sensor itself is an electronic component subjected to intense heat and vibration; buying new is strongly recommended.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For the wiring harness, check for flexible, intact insulation without any cracks or chew marks.
• Ensure the plastic connector is not brittle and the locking tab is intact.
• Verify the donor vehicle shows no signs of a front-end fire or excessive engine bay heat.

OEM-only on this vehicle (don't cheap out):

• Knock Sensor

Aftermarket brands forum-validated for this vehicle:

• Denso (often the Original Equipment Manufacturer)
• NTK

Brands owners have reported issues with on this vehicle:

• Cheap, unbranded sensors from eBay or Amazon are frequently reported by owners to be dead-on-arrival or fail shortly after installation, causing the P0325 code to return immediately.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

Frequently Asked Questions