P0325 - OBD-II Trouble Code

Auto Systems and Repair

Knock Sensor #1 - Circuit Malfunction (Single Sensor or Bank 1) 

Our emissions expert has put together the following information about the P0325 fault code. We have also included diagnostic procedures you can take to your repair shop if the mechanic is having difficulty analyzing the code.

OBD II Fault Code

  • OBD II P0325

Fault Code Definition

  • Knock Sensor #1 - Circuit Malfunction (Single Sensor or Bank 1)
What does this mean?
The purpose of the knock sensor is to alert the PowerTrain Control Module or PCM that the engine is pinging or knocking. This is important because a pinging or knocking engine pollutes the air with poisonous Nitrogen Oxide gases that cause acid rain and promote respiratory diseases such as asthma. 

Code P0325 indicates that the readings from the #1 Knock Sensor circuit are too low, too high, erratic or in some way outside of its operational window and malfunctioning.

Symptoms

  • Check Engine Light will illuminate
  • Engine pings on accelration
  • Engine may be running hotter than normal
  • In rare cases, the engine may not exhibit noticeable symptoms

Common Problems That Trigger the P0325 Code

  • Defective Knock Sensor
  • Defective Knock Sensor Circuit or connections
  • Defective EGR System
  • Malfunctioning Cooling System
  • Lean air/fuel ratio

Common Misdiagnosis

  • Knock Sensor replaced when cause of code P0325 was a cooling system problem
  • Knock Sensor replaced when cause of code P0325 was an EGR system malfunction
Want to learn more?
The PowerTrain Control Module or PCM controls the degree of ignition system spark advance in order to achieve maximum power and fuel economy. When the knock sensor signals the PowerTrain Control Module or PCM that the engine is pinging or knocking, the first thing the PCM does is change the amount of timing advance by retarding it in controlled increments, until the knock sensor stops signaling the PCM that the engine is pinging. 

P0325 Diagnostic Theory for Shops and Technicians
Code P0325 is triggered because the PCM knows that the signal from the #1 knock sensor circuit is outside of its normal operational window, is malfunctioning and/or there is an extraordinary engine condition. Capture and document the freeze frame data so you have an idea of what operational conditions were present when the PCM triggered the P0325 code. Then do a visual inspection of the engine and cooling system, coolant level/condition and oil level/condition to verify that code P0325 wasn't caused by a failure of a mechanical system. Then start the engine and rev it a few times to see that it operates normally, making sure there isn't a severe mechanical condition such that, driving the vehicle could cause further damage. Test drive the vehicle with a data streaming scanner and pay close attention to the #1 Knock Sensor PID and the PID for timing advance. How is the knock sensor #1 circuit operating? Is it sending/not sending signals when the engine is pinging or not pinging? If so, find out why. Sometimes I bring the car back to the service bay and tap the engine with a small hammer and watch the knock sensor PID as well as the PID for timing advance. 
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