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Severity: Low Code type: Generic (all makes)

P0327 Code: Knock Sensor 1 Circuit Low Input (Bank 1)

Knock sensor 1's signal is too weak or pulled to ground: usually wiring, water or a loose sensor.

At a glance

Severity: 2/5 – Low2/5

Severity: Low

Meaning
Knock Sensor 1 Circuit Low Input (Bank 1)
System
Ignition & Misfire · Powertrain
Safe to drive?
Yes, short term
Typical repair cost
$80–$1,100
DIY difficulty
Moderate

P0327 means the signal from knock sensor 1 (bank 1, or the single sensor) is below the lowest level the engine computer considers possible. Many computers put a small bias voltage on the knock signal wire and also expect a minimum amount of vibration signal once the engine is running. When the bias voltage is dragged toward zero, or the sensor produces almost nothing, P0327 sets. On many designs an open circuit reads as low input too. The most common reasons are a wire shorted to ground, a corroded or water-filled connector, a sensor that isn't tight against the block, or a cracked sensor. On V engines the sensor often sits in the valley under the intake manifold, where water or coolant can collect and slowly destroy the connector.

Can I keep driving? Safe to drive in normal use. Use the recommended octane or higher and avoid towing or long full-throttle runs, since the computer is now running conservative timing without knock feedback.

How to read P0327

How to read P0327P10233274
  1. P Powertrain
  2. 0 Generic (SAE)
  3. 3 Ignition / misfire
  4. 27 Specific fault

Symptoms

  • Check-engine light on, usually without other warning lights
  • Sluggish acceleration and slightly lower mpg
  • Pinging under hard acceleration that the computer no longer catches
  • Code that appeared after the intake manifold was removed for other work
  • Code that comes back after rain or engine washing

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Signal wire chafed and shorted to ground, often under the intake or against the block 28%
  2. Water or coolant in the valley corroding the sensor connector 22%
  3. Open circuit: broken wire or a connector not clicked in after previous work 18%
  4. Sensor loose or under-torqued, so it passes too little vibration 14%
  5. Knock sensor cracked or internally shorted 13%
  6. Engine computer knock input failure 5%

Diagnosis step by step

Diagnostic flow: P03271Measure the bias voltage at theharness2Check the sensor for a short toground3Inspect for water and corrosion4Check harness continuity to thecomputer5Reinstall at the correct torque

  1. Measure the bias voltage at the harness

    Key on, engine off, back-probe the knock signal wire and measure DC voltage to ground, then compare with service information. Many systems show a few volts here. A reading of zero points to a short to ground in the harness or sensor; unplug the sensor and measure again to see which.

    Tools: Multimeter

  2. Check the sensor for a short to ground

    With the sensor unplugged, measure resistance from each sensor terminal to the engine block. It should read open or very high. Also measure across the terminals: sensors with a built-in resistor should match the spec closely, for example around 100 kilohms on many GM sensors.

    Tools: Multimeter

  3. Inspect for water and corrosion

    Look at where the sensor lives. On V8s with sensors in the valley, pull the intake if needed and look for standing water, coolant residue or rust around the sensor and connector. Find the leak path, such as a cowl drain or intake coolant passage, before installing new parts.

    Tools: Flashlight

  4. Check harness continuity to the computer

    With the battery disconnected, check each wire from the sensor connector to the computer connector for continuity and for shorts to ground, flexing the harness as you go. Watch for insulation crushed under intake bolts or brackets.

    Tools: Multimeter

  5. Reinstall at the correct torque

    Clean the mounting face, fit a new sensor if needed and torque it to spec, often around 15 lb-ft. On V engines, replace the sub-harness at the same time if it's brittle, since the intake has to come off anyway.

    Tools: Torque wrench

Where the parts are

Ignition: coils and spark plugs per cylinder – P03271234567
Ignition: coils and spark plugs per cylinder
  1. 1Ignition coil
  2. 2Spark plug
  3. 3Fuel injector
  4. 4Camshaft sensor
  5. 5Crankshaft sensor
  6. 6Engine computer (ECM)
  7. 7Intake manifold

Repair options & costs

RepairDIY?Estimated cost
Clean and seal corroded knock sensor connector Yes $80–$220
Repair shorted or broken wire No $100–$350
Replace knock sensor (block side, accessible) Yes $150–$400
Replace knock sensors and harness under the intake (V8 valley) No $500–$1,100

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Notes by brand

Chevrolet

On earlier Gen III small-block V8s in GM trucks, the knock sensors sit in the valley under the intake manifold, where water and coolant can collect and corrode them. Later Gen IV engines moved the sensors to the sides of the block. On both, low-input codes are more often corrosion or wiring than a dead sensor, and the sensors must be torqued to spec to read correctly.

Emissions / smog test impact

Will fail

A P0327 with the check-engine light on fails an OBD emissions test even though emissions are usually normal. Clear the code only after the repair and let the monitors finish before testing.

Frequently asked questions

What's the difference between P0327 and P0328?

P0327 means the signal is too low: typically a short to ground, open wiring, water in the connector or a loose sensor. P0328 means it's too high, from a short to voltage, electrical interference or excessive engine noise. The fixes are different, so read the exact code.

Why did P0327 show up right after my intake gasket job?

On many V engines the knock sensor and its harness are under the intake. A connector that wasn't clicked in, a wire pinched under a bolt or a sensor bumped loose during the job are all common. Recheck that area first.

Can water really get to a sensor under the intake?

Yes. Water from a blocked cowl drain, pressure washing or a coolant leak at the back of the intake can pool in the valley. Over time it corrodes the sensor and connector, which pulls the signal low.

Do I need to replace both knock sensors?

Not always, but on engines where both sit under the intake, many technicians do both along with the harness, since the labor to get there is the same and the parts are inexpensive by comparison.

Sources