P0325: P0325 Diagnostic Guide

What this code means

P0325 may indicate that the engine control module is not receiving the expected Knock Sensor 1 signal.

What the vehicle may do

The vehicle may run with reduced power or changed ignition timing strategy.
The driver may notice little obvious change, or may notice different engine response under load.

Possible fault areas

Possible knock sensor signal circuit issues
Possible wiring, terminal, or connector concerns
Possible knock sensor condition or mounting-related concerns
Possible control module involvement in the correct diagnostic branch

Diagnostic path

Opening: what P0325 means

On this 2014 to 2018 GMC Sierra 1500 with the 5.3 gas engine, P0325 points us toward the Knock Sensor 1 signal circuit. In plain terms, the control module may not be seeing the sensor signal it expects, and this code is treated as an open signal circuit fault. The truck may still run, but it can retard ignition timing to protect the engine from damaging knock, so the customer may notice reduced power or a different engine response. Broadly, possible fault areas can include the knock sensor circuit, the sensor connection, wiring or terminal issues, sensor condition, or in the right branch, the engine control module. Before getting deep into it, start with the basic system checks, follow a structured diagnostic approach, and make sure you understand the test setup before backprobing or disconnecting anything.

Monitor gate and setting logic

For P0325, treat the running conditions as a monitor gate, not as a parts diagnosis. The open-circuit monitor runs with the engine running for greater than 200 engine revolutions and for greater than 2 s, with engine speed from 400 to 5,500 RPM for greater than 75 engine revolutions. The code sets when the signal circuit is open for greater than 5 s. In the related circuit-fault logic, a signal circuit short to ground for greater than 5 s, or a signal circuit short to voltage for greater than 5 s, points you down different branches. That timing helps separate an open-circuit P0325 path from the other signal-circuit faults in the same knock sensor family.

Initial verification before circuit testing

With the engine running, check whether P0325 is present by itself or whether other knock sensor or module-related faults are also stored. If other codes are present, check what they mean first instead of forcing every fault through the P0325 path. If this signal-circuit fault is the one you are chasing, move into circuit testing. If the relevant codes are not currently set, look at the scan data. Cylinder 1 through 8 Knock Detected should read No. While watching that parameter, wiggle the harness and connector at the B68 Knock Sensor, then wiggle the harness and connector at the K20 Engine Control Module. If the parameter changes during that movement, repair the wiring, terminals, or connector problem as necessary. If the code is not currently active, reproduce the operating conditions, or reproduce the captured conditions from the fault data, then verify whether the code resets. If it does not reset, call it all OK for now. If it resets, continue with circuit testing.

Related knock-performance checks, only if the path points there

If the scan and code direction points away from the open-circuit P0325 path and toward a knock-performance type concern, do not skip the mechanical checks. Inspect the B68 Knock Sensor for correct installation, interference from brackets, wiring, hoses, lines, or other nearby parts, and visible damage. The sensor mounting surface needs to be clean and free of burrs, casting flash, and foreign material. Also keep in mind that overtightening the retaining bolt, or dropping the sensor, can damage it. If the sensor area checks out, look for vehicle conditions that can create knock or noise, like accessory drive issues, belt-driven device problems, engine mechanical condition, or contaminated or poor-quality fuel. If all of those checks are normal on that branch, the path allows testing or replacing the B68 Knock Sensor.

Circuit testing: terminal 2/B

Now for the P0325 circuit test. Turn the ignition and vehicle off, then disconnect the appropriate electrical connector at the B68 Knock Sensor. Turn the ignition on with the vehicle in service mode. The control module input for signal terminal 2/B has internal resistance connected to 1.33 V, so test between signal circuit terminal 2/B and ground. You should see 1 to 2 V. If terminal 2/B is less than 1 V, turn the ignition and vehicle off, disconnect the appropriate K20 Engine Control Module connector, and test terminal 2/B at the component harness to ground for infinite resistance. If it is less than infinite resistance, repair the short to ground. If resistance is infinite, test from terminal 2/B at the component harness to the other end of the circuit at the control module harness. You should have less than 2 Ω. If it is 2 Ω or greater, repair the open or high resistance in the circuit. If it is less than 2 Ω, that branch calls for replacing the K20 Engine Control Module. If terminal 2/B is greater than 2 V, turn the ignition and vehicle off, disconnect the K20 Engine Control Module connector, turn the ignition back on in service mode, and test terminal 2/B at the component harness to ground for less than 1 V. If it is 1 V or greater, repair the short to voltage. If it is less than 1 V, that branch calls for replacing the K20 Engine Control Module.

Circuit testing: terminal 1/A

If terminal 2/B is in range at 1 to 2 V, move to signal terminal 1/A. The control module input for terminal 1/A has internal resistance connected to 5 V. Test between signal circuit terminal 1/A and ground. The expected reading is 2 to 4 V. If terminal 1/A is less than 2 V, turn the ignition and vehicle off, disconnect the appropriate K20 Engine Control Module connector, and test terminal 1/A at the component harness to ground for infinite resistance. If it is less than infinite resistance, repair the short to ground. If resistance is infinite, test terminal 1/A from the component harness to the other end of the circuit at the control module harness. You should have less than 2 Ω. If it is 2 Ω or greater, repair the open or high resistance in the circuit. If it is less than 2 Ω, that branch calls for replacing the K20 Engine Control Module. If terminal 1/A is greater than 4 V, turn the ignition and vehicle off, disconnect the K20 Engine Control Module connector, turn the ignition on in service mode, and test terminal 1/A at the component harness to ground for less than 1 V. If it is 1 V or greater, repair the short to voltage. If it is less than 1 V, that branch calls for replacing the K20 Engine Control Module. If terminal 1/A is between 2 and 4 V after terminal 2/B also tested correctly, the path calls for replacing the appropriate B68 Knock Sensor.

Repair verification and takeaway

After the repair, keep verification separate from testing. Verify the repair and confirm the code stays gone under the proper operating conditions. Bottom line: for P0325, do not guess at the sensor first. Prove the signal circuits, check the harness and connector behavior, and only follow the replacement branch when the test results put you there. For more diagnostic training, visit stepdiagnostics.com.