P0325
DTC P0325: Knock Sensor CircuitCAUTION: If DTC P0325 has been set, TCL related DTC U1120 is also set. After P0325 has been diagnosed, don't forget to erase DTC U1120.
Knock Sensor Circuit Part 1:
Knock Sensor Circuit Part 2:
CIRCUIT OPERATION
- The knock sensor sends a signal voltage to the ECM
TECHNICAL DESCRIPTION
- The knock sensor converts the vibration of the cylinder block into a voltage and outputs it. If there is a malfunction of the knock sensor, the voltage output will not change.
- The ECM
DTC SET CONDITIONS
Check Conditions
- 2 seconds or more have passed since the starting sequence was completed.
- Engine speed is higher than 2,500 r/min.
- Volumetric efficiency is 40 percent or more.
Judgement Criterion
- Knock sensor output voltage (knock sensor peak voltage in each 1/2 turn of the crankshaft) has not changed more than 0.06 volt in the last consecutive 200 periods.
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Knock sensor failed.
- Open or shorted knock sensor circuit, harness damage or connector damage.
- ECM failed.
- PCM failed.
DIAGNOSIS
Required Special Tools:
- MB991958: Scan Tool (MUT-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991910: Main Harness A
STEP 1. Check harness connector B-126 at the knock sensor for damage.
Q: Is the harness connector in good condition?
YES: Go to Step 2.
NO: Repair or replace it. Then go to Step 6.
STEP 2. Check the continuity at knock sensor harness side connector B-126.
1. Disconnect the connector B-126 and measure at the harness side.
2. Check for the continuity between terminal No. 2 and ground.
- Should be less than 2 ohms.
Q: Does continuity exist?
YES: Go to Step 3.
NO: Repair harness wire between knock sensor connector B-126 (terminal No. 2) and ground because of open circuit or harness damage. Then go to Step 6.
STEP 3. Check harness connector B-20 at ECM
Q: Is the harness connector in good condition?
YES: Go to Step 4.
NO: Repair or replace it. Then go to Step 6.
STEP 4. Check for open circuit and short circuit to ground and harness damage between knock sensor connector B-126 (terminal No. 1) and ECM
Q: Is the harness wire in good condition?
YES: Go to Step 5.
NO: Repair it. Then go to Step 6.
STEP 5. Check the knock sensor.
1. Disconnect the knock sensor connector B-126.
2. Start the engine and run at idle.
3. Measure the voltage between knock sensor side connector terminal No. 1 (output) and No. 2 (ground).
4. Gradually increase the engine speed.
- The voltage increases with the increase in the engine speed.
5. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?
YES: Replace the ECM or the PCM. When the ECM or the PCM is replaced, register the encrypted code. Refer to Encrypted Code Registration Criteria Table in Antitheft and Alarm Systems. Then go to Step 6.
NO: Replace the knock sensor. Then go to Step 6.
STEP 6. Using scan tool MB991958, read the diagnostic trouble code (DTC).
CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
1. Connect scan tool MB991958 to the data link connector.
2. Turn the ignition switch to the "ON" position.
3. Erase the DTC.
4. Test drive under the following conditions:
- Engine speed: 3000 - 5000 r/min
- Engine load: 40% or more
- Drive a minimum of 3 seconds after the above conditions have been met.
5. After completing the test drive, read the DTC. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is DTC P0325 set?
YES: Retry the troubleshooting.
NO: The inspection is complete.