P0325: Knock Sensor 1 Circuit

What this code means

P0325 means the PCM may be seeing a knock sensor circuit signal that does not look electrically believable.

What the vehicle may do

The MIL may illuminate.
The vehicle may seem to run normally in some cases.
Driveability changes can be possible depending on how the PCM responds.

Possible fault areas

Possible knock sensor signal circuit fault.
Possible knock sensor return circuit fault.
Possible connector or terminal problem.
Possible knock sensor concern.
Possible PCM involvement after other circuit checks are exhausted.

Diagnostic path

Opening context and monitor logic

On this Ram 1500 Classic with the 3.6 Pentastar, P0325 is for the Knock Sensor 1 circuit. In plain terms, the PCM is seeing a knock sensor signal that does not look electrically believable. The driver may only notice the MIL, and the truck may otherwise seem normal, but the possible fault areas include the knock sensor signal side, the return side, connector issues, the sensor itself, and, after the circuit checks are exhausted, the PCM. Before getting deep into the circuit, start with the basic system checks. For this code, the monitor gate is engine speed above 2000 rpm, battery voltage between 7.5 volts and 15.8 volts, and barometric pressure above 75.2 kPa. The code sets when the PCM sees Knock Sensor input voltage above 4.8 volts, or less than 0.2 volts when engine speed is above 2000 rpm.

Confirm whether P0325 is active

Start by finding out whether P0325 is active or pending. Start the engine, then test drive or operate the vehicle under the same conditions that allow this monitor to run and set. Use the scan tool to read and record the DTCs. If P0325 is not active or pending, handle it as an intermittent condition. If it is active or pending, move into the circuit testing.

Check the signal circuit for short to voltage

Before probing at the PCM side, do not back-probe or probe the PCM harness connectors. That can damage the PCM terminals and create a poor terminal-to-pin connection. Use the GPEC Diagnostic Adaptor for this diagnosis. With the ignition off, disconnect the Knock Sensor harness connector. Turn the ignition on and measure voltage on the K42 Knock Sensor 1 Signal circuit at the Knock Sensor harness connector. If that voltage is above 5.2 volts, repair the K42 signal circuit for a short to voltage, then verify the repair and confirm the code stays gone. If it is not above 5.2 volts, continue to the next check.

Check the signal circuit for open or high resistance

Turn the ignition off. Disconnect the PCM C2 harness connector and connect the GPEC Diagnostic 10436 adaptor. Now measure resistance of the K42 Knock Sensor 1 Signal circuit from the Knock Sensor harness connector to the GPEC adaptor. The circuit should measure below 3.0 Ohms. If it does, keep going. If it does not, repair the K42 signal circuit for an open or high resistance, then verify the repair and confirm the code stays gone.

Check the return circuit for open or high resistance

Next, check the K942 Knock Sensor 1 Return circuit. Measure resistance from the Knock Sensor harness connector to the GPEC adaptor. This circuit also needs to be below 3.0 Ohms. If it is below 3.0 Ohms, continue. If it is not, repair the K942 return circuit for an open or high resistance, then verify the repair and confirm the code stays gone.

Check for a short between signal and return

Now check whether the signal and return circuits are shorted together. Check continuity between the K42 Knock Sensor 1 Signal circuit and the K942 Knock Sensor 1 Return circuit at the Knock Sensor harness connector. If there is continuity between those two circuits, repair the short between the K42 signal circuit and the K942 return circuit, then verify the repair and confirm the code stays gone. If there is no continuity, keep moving through the path.

Check the signal circuit for short to ground

Next, check the K42 Knock Sensor 1 Signal circuit for a short to ground. Check continuity between ground and the K42 signal circuit at the Knock Sensor harness connector. If there is continuity to ground, repair the K42 signal circuit for a short to ground, then verify the repair and confirm the code stays gone. If there is no continuity to ground, the circuit checks have not found the fault, so move to the sensor step.

Replace Knock Sensor 1 and retest

At this point, replace Knock Sensor 1. Reconnect the Knock Sensor and PCM harness connectors, turn the ignition on, and erase the DTCs with the scan tool. Then operate the vehicle under the captured conditions, or under the same monitor conditions that set the code, and read DTCs again. If P0325 does not return, replacing Knock Sensor 1 repaired the fault; verify the repair and confirm the code stays gone. If the code does return, continue into the harness and connection inspection.

Inspect related harness connections

For the connection check, disconnect all PCM harness connectors, any related in-line harness connectors if equipped, and the related component connectors. Inspect the connectors and terminals for installation problems, damaged locks, corrosion, water intrusion, seal damage, bent terminals, overheated or discolored terminals, pushed-back terminals, spread terminals, and terminal tension concerns. Repair anything found. Then reconnect the PCM connectors, in-line connectors if equipped, and component connectors, making sure everything is fully seated and the locks are engaged. Erase the DTCs, test drive or operate the vehicle under the conditions that set the code, and read DTCs again. If P0325 does not return, the wiring or poor connection problem has been repaired. If it does return after those checks and repairs, replace and program the PCM, then verify the repair and confirm the code stays gone.

Closing takeaway

The clean path on P0325 is to prove the circuit first: short to voltage, open or high resistance on signal and return, signal-to-return short, and short to ground. Only after those checks pass does the path move to Knock Sensor 1, then connector integrity, and finally the PCM if the code still returns. For more diagnostic training, visit stepdiagnostics.com.