engine

Knock Sensor

for 2021 Honda Civic 1.5L I4 Turbo · FWD

Difficulty

Moderate

Time

2.0 h

Tools

Steps

This procedure covers the removal and replacement of the knock sensor on the 2016-2021 Honda Civic 1.5L turbocharged engine, which is located on the engine block beneath the intake manifold.

Warnings

⚠️Allow engine to cool completely before starting work. Coolant system is pressurized and can cause severe burns.

⚠The knock sensor is torque-critical for proper operation. Under-torquing will cause false knock detection; over-torquing can damage the sensor.

⚠Do not drop the knock sensor as internal piezoelectric element can be damaged without visible external damage.

ℹ️The engine cover and portions of the intake system must be removed to access the knock sensor on this engine.

Tools required

10mm socket and ratchetEssential

12mm socket and ratchetEssential

19mm deep socketEssential

Torque wrench (10-50 Nm range)Essential

Extension set (3-inch and 6-inch)Essential

Flathead screwdriver

Wire brush

Shop towelsEssential

Coolant drain panEssential

Anti-seize compound

Parts

Knock sensor × 1 — Use OEM Honda specification
Intake manifold gasket (if damaged) × 1 — Use OEM Honda specification

Fluids

Honda Type 2 Coolant (Blue) — 1 qt

Preparation

Ensure engine is completely cool to the touch (wait at least 2 hours after last operation)
Disconnect negative battery terminal and wait 3 minutes for system power-down
Remove engine cover by pulling upward on front edge, then lifting away from rear mounting grommets
Place drain pan under radiator and drain approximately 1 quart of coolant by opening radiator petcock to reduce coolant loss during hose removal

Procedure

1
Remove air intake components
Disconnect the mass airflow sensor electrical connector. Loosen the air intake tube clamp at the throttle body using a flathead screwdriver. Remove the air intake tube and air box assembly by releasing mounting clips and lifting away from engine bay. Set aside in clean area.
2
Disconnect intake manifold coolant hoses
Locate the two coolant hoses connected to the intake manifold (used for EGR warming). Squeeze the spring clamps with pliers and slide back on hoses. Twist and pull hoses from manifold fittings. Plug hose ends with shop towels to minimize coolant spillage.
⚠Even with partial draining, residual coolant will spill. Have shop towels ready and avoid getting coolant on drive belt.
3
Remove intake manifold mounting bolts
Disconnect electrical connectors from throttle body and MAP sensor. Using a 10mm socket, remove the intake manifold cover bolts (4 total). Using a 12mm socket, remove the six intake manifold mounting bolts in reverse of tightening sequence (start from outside bolts, work toward center). Keep bolts organized by location.
ℹ️Note routing of any vacuum lines and wiring harnesses attached to manifold before removal.
Torque spec
Cover Bolts15 Nm (11 lb-ft)
4
Remove intake manifold
Disconnect any remaining vacuum hoses and wiring clips from intake manifold. Carefully lift intake manifold upward and away from cylinder head. Inspect gasket condition. If gasket is damaged or shows signs of deterioration, it must be replaced. Cover open intake ports on cylinder head with clean shop towels to prevent debris entry.
⚠Do not allow any debris or tools to fall into open intake ports. Foreign objects can cause severe engine damage.
5
Locate and access knock sensor
With intake manifold removed, locate the knock sensor on the rear side of the engine block, below where the intake manifold was positioned. The sensor will have a single wire connector. Press the locking tab and disconnect the electrical connector from the knock sensor.
6
Remove knock sensor
Using a 19mm deep socket with extension, carefully loosen and remove the knock sensor from the engine block. Turn counterclockwise to remove. Avoid striking or dropping the sensor during removal. Inspect the sensor mounting surface on the engine block for corrosion or debris.
ℹ️The sensor may be tight due to corrosion. Apply penetrating oil if needed and allow to soak for 10 minutes before removal.
7
Prepare engine block mounting surface
Clean the knock sensor mounting hole and surrounding area on the engine block using a wire brush. Remove all dirt, oil, and corrosion. The mounting surface must be clean and dry for proper sensor operation. Wipe clean with shop towel. Inspect threads in block for damage.
8
Install new knock sensor
Thread the new knock sensor into the engine block by hand, ensuring it starts straight and threads smoothly. Do NOT apply anti-seize to knock sensor threads - the sensor must have direct metal-to-metal contact for proper grounding. Once hand-tight, use torque wrench with 19mm socket to tighten to specification.
⚠CRITICAL: Do not use anti-seize or thread sealant on knock sensor. The sensor requires direct electrical ground through its threads to function properly.
Torque spec
Knock Sensor20 Nm (15 lb-ft)
9
Reconnect knock sensor electrical connector
Connect the electrical connector to the knock sensor, ensuring it clicks into place securely. Verify the connector locking tab is fully engaged. Route the wire harness to avoid contact with hot exhaust components or moving parts.
10
Reinstall intake manifold
Remove shop towels from intake ports. Position new or inspected gasket onto cylinder head (gasket has locating tabs). Carefully lower intake manifold into position, ensuring gasket remains properly aligned. Install all six mounting bolts hand-tight, then torque in sequence from center outward using torque wrench.
Torque spec
Gasket Bolts19 Nm (14 lb-ft)
11
Reinstall intake manifold cover and connections
Install intake manifold cover and tighten cover bolts to specification. Reconnect throttle body and MAP sensor electrical connectors. Reconnect all vacuum hoses to their original positions. Reinstall coolant hoses to intake manifold fittings and secure with spring clamps.
Torque spec
Cover Bolts15 Nm (11 lb-ft)
12
Reinstall air intake system
Reinstall air box assembly and air intake tube. Tighten intake tube clamp at throttle body securely. Reconnect mass airflow sensor electrical connector. Ensure all connections are secure and no tools or parts are left in engine bay.
13
Refill coolant and check for leaks
Refill cooling system with Honda Type 2 (Blue) coolant to proper level. Start engine and allow to warm to operating temperature with heater on full hot. Check for coolant leaks at intake manifold hose connections. Add coolant as needed to reach proper level in reservoir. Check for any vacuum leaks by listening for hissing sounds.
⚠Monitor temperature gauge during warm-up. If engine overheats, shut off immediately and check for proper coolant fill and air pockets in system.

Reassembly

Reinstall engine cover by aligning rear mounting grommets first, then pressing down on front clips until secured
Reconnect negative battery terminal and tighten securely
Clear any diagnostic trouble codes using OBD-II scanner if knock sensor codes were present

Verification

Start engine and verify it runs smoothly without rough idle or unusual noises
Check that no coolant leaks are present at intake manifold hose connections after engine reaches operating temperature
Use OBD-II scanner to verify no knock sensor related codes are present (P0325, P0327, P0328)
Perform test drive and verify engine operates normally under acceleration with no spark knock or detonation
Monitor engine performance over next few days to ensure knock sensor is functioning properly and no codes return