Code No. P0325: Detonation Sensor System

OPERATION

A power voltage of 5 V is applied to the detonation output terminal (terminal No. 2) from the engine-ECU (terminal No. 20).
The power voltage is earthed to the engine-ECU (terminal No. 21) from the detonation sensor (terminal No. 1).

FUNCTION

The detonation sensor detects the vibration of the cylinder block caused by detonation waves, and inputs a signal to the engine-ECU.
In response to the signal, the engine-ECU provides controls to retard the ignition timing when the detonation occurs.

TROUBLE JUDGMENT

Check Conditions

After 2 seconds have passed since the engine starting sequence was completed.
Engine speed is 2,500 r/min or higher.

Judgment Criterion

Change of detonation sensor output voltage (detonation sensor peak voltage in each 1/2 turn of the crankshaft) has not been 0.06 V or more in the last consecutive 200 periods.

PROBABLE CAUSES

Failed detonation sensor
Open/short circuit and damage in detonation sensor circuit or loose connector contact
Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Connector check: A-122 detonation sensor connector

Q. Is the check result normal?

Go to Step 2 .

Repair or replace the connector.

STEP 2. Perform resistance measurement at A-122 detonation sensor connector.

Disconnect connector, and measure at harness side.
Resistance between terminal No. 1 and earth.

OK: Continuity (2 Ω or less)

Q. Is the check result normal?

Go to Step 6 .

Go to Step 3 .

STEP 3. Connector check: A-34 engine-ECU connector

Q. Is the check result normal?

Go to Step 4 .

Repair or replace the connector.

STEP 4. Check harness between A-122 (terminal No. 1) detonation sensor connector and A-34 (terminal No. 21) engine-ECU connector.

Check earthing line for open circuit and damage.

Q. Is the check result normal?

Go to Step 5 .

Repair the damaged harness wire.

STEP 5. Replace detonation sensor.

After replacing the detonation sensor, re-check the trouble symptoms.

Q. Does trouble symptom persist?

	Replace the engine-ECU then perform the variant coding (Refer to GROUP 00 - Precautions Before Service - How to Perform Variant Coding ).

	Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).

STEP 6. Perform voltage measurement at A-122 detonation sensor connector.

Disconnect connector, and measure at harness side.
Ignition switch: ON
Voltage between terminal No. 2 and earth.

OK: 4.5 - 4.9 V

Q. Is the check result normal?

GO to Step 11 .

Go to Step 7 .

STEP 7. Perform voltage measurement at A-34 engine-ECU connector.

Disconnect engine-ECU connector, and connect special tool power plant ECU check harness (MB991987), and then measure the voltage on the check connector.
Disconnect A-122 detonation sensor.
Ignition switch: ON
Voltage between terminal No. 20 and earth.

OK: 4.5 - 4.9 V

Q. Is the check result normal?

Go to Step 8 .

Go to Step 9 .

STEP 8. Connector check: A-34 engine-ECU connector

Q. Is the check result normal?

Check output line for open circuit.

Repair or replace the connector.

STEP 9. Connector check: A-34 engine-ECU connector

Q. Is the check result normal?

Go to Step 10 .

Repair or replace the connector.

STEP 10. Check harness between A-122 (terminal No. 2) detonation sensor connector and A-34 (terminal No. 20) engine-ECU connector

Check output line for short circuit.

Q. Is the check result normal?

Go to Step 5 .

Repair the damaged harness wire.

STEP 11. Check harness between A-122 (terminal No. 2) detonation sensor connector and A-34 (terminal No. 20) engine-ECU connector

Check output line for damage.

Q. Is the check result normal?

Go to Step 12 .

Repair the damaged harness wire.

STEP 12. M.U.T.-III diagnosis code.

Reconfirmation of diagnosis code.

Q. Is the diagnosis code set?

	Go to Step 13 .

	Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).

STEP 13. Replace the detonation sensor.

After replacing the detonation sensor, re-check the trouble symptoms.

Q. Does trouble symptom persist?

	Replace the engine-ECU then perform the variant coding (Refer to GROUP 00 - Precautions Before Service - How to Perform Variant Coding ).

	Check end.