An illuminated check engine light on a customer’s 1998 Honda Accord EX, that is registering a trouble code P0325, could be caused by the knock sensor, the connection, wire harness or the Engine Control Module (ECM). Replace the knock sensor and the trouble code resets.

Tests:
1. With the knock sensor unplugged and using a digital volt ohmmeter (DVOM), check for 0.02V to 0.03V reference voltage from the ECM to the knock sensor.

 

2. Next use a scope and look for an AC voltage signal from the knock sensor when the engine rpm is increased. It should have a very rapid AC voltage pattern of 1V positive and 1V negative. If the signal is OK, verify that signal is correct back to the ECM. If there is no harness or knock sensor problem, always verify the connection at the ECM before replacing the ECM.

 

Tech Tip:
The knock sensor harness is a shielded wire, so also unplug the alternator and verify that there is no interference in that circuit.

Courtesy of Identifix.

For more information, visit www.identifix.com.