What Does P1323 Mean?
P1323 indicates that knock sensor 4 is producing a signal below the expected minimum voltage. Like P1321 for sensor 3, this low-input condition means the sensor's ability to detect detonation is compromised. Knock sensor 4 provides coverage for a specific zone on larger displacement engines.
Common Causes
30%
Degraded knock sensor 4 piezoelectric element
25%
High resistance connection at the knock sensor 4 connector
20%
Loose sensor mounting causing poor vibration coupling
15%
Corroded or damaged wiring in the sensor circuit
10%
ECM knock sensor 4 input circuit degradation
Diagnostic Steps
1
Verify knock sensor 4 is tightened to the manufacturer's specified torque — undertightened sensors have poor acoustic coupling.
2
Clean and inspect the sensor connector for oxidation or terminal damage.
3
Measure sensor output with an oscilloscope while tapping near the sensor — output should be similar to other knock sensors.
4
Check wiring continuity and resistance from the sensor to the ECM.
5
If the sensor and wiring test good, compare signal levels across all knock sensors during a steady-state engine operation to rule out ECM input issues.
Estimated Repair Cost
$100 - $400
Parts + labor, varies by vehicle and location
P1323 indicates that knock sensor 4 is producing a signal below the expected minimum voltage. Like P1321 for sensor 3, this low-input condition means the sensor's ability to detect detonation is compromised. Knock sensor 4 provides coverage for a specific zone on larger displacement engines.
The most common cause of P1323 (Knock Sensor 4 Circ. Low Input) is: Degraded knock sensor 4 piezoelectric element
Typical repair costs for P1323 range from $100 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A low-output knock sensor leaves the ECM partially blind to detonation in the sensor 4 zone, risking engine damage from undetected pre-ignition or detonation, especially under high load.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1323 to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Knock Detection / Ignition Timing
Difficulty
Type
Manufacturer
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