Circuit Description
The knock sensor (KS) system is used in order to detect any engine detonation, or spark knock. The engine control module (ECM) will retard the spark timing based on the signals from the KS. The knock sensors produce an AC voltage that is sent to the ECM. The amount of AC voltage produced is proportional to the amount of knock.
An operating engine produces a normal amount of engine mechanical vibration, or noise. The knock sensors will produce an AC voltage signal from this noise. When the engine is operating, the ECM will learn the minimum and maximum frequency of the noise the engine produces. When the ECM determines that this frequency is less than or more than the expected amount, a knock sensor diagnostic trouble code (DTC) will set.
Conditions for Running the DTC
| • | The engine coolant temperature (ECT) is more than 40°C (104°F). |
| • | The engine has idled for 5 seconds allowing the ECM to learn a minimum engine noise level. |
| • | The engine has been running at least 10 seconds. |
| • | The engine speed is more than 2,000 RPM. |
Conditions for Setting the DTC
The ECM does not detect a difference between the minimum learned engine noise level at idle and the engine noise between 2,500-3,500 RPM for 5 seconds.
Action Taken When the DTC Sets
| • | The control module stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records. |
| • | The driver information center, if equipped, may display a message. |
Conditions for Clearing the DTC
| • | A current DTC Last Test Failed clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | Clear the DTC with a scan tool. |
Diagnostic Aids
Use the J 35616 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector. Using this kit prevents damage to the harness or component terminals. Refer to Using Connector Test Adapters in Wiring Systems. For an intermittent, refer to Symptoms - Engine Controls .
Check for the following conditions:
| • | The KS shielded wiring for continuity or damage--By rolling back the boot on the KS connector that leads back to the ECM, the shrink wrap will be exposed. Carefully insert a test lamp connected to B+ under the shrink wrap. Good KS shield continuity will illuminate the test lamp. |
| • | Damaged harness--Inspect the wiring harness for any damage. If the harness appears to be OK, connect the DMM to the signal and reference ground at the ECM connector. Monitor the resistance of the circuit while moving the harness in different locations. A fluctuation in the resistance will indicate the area of a possible concern. |
| • | Damaged KS lead--If the sensor lead is damaged in any way the sensor must be replaced. |
| • | Poor connections at the ECM or at the component--Inspect the sensor harness connector and the ECM connections for poor terminal tension or signs of corrosion. |
| • | Misrouted harness--Inspect the harness in order to ensure that the harness is routed correctly. |
| • | The knock sensor for proper installation--A knock sensor that is loose or over torqued may cause this DTC to set. |
If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step verifies that the malfunction is present.
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This test determines if the KS is capable of producing a signal.
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This test verifies the integrity of the KS signal and reference ground circuits up to the ECM connector.
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These tests address any faults in the KS signal and reference ground circuits from the ECM to the harness connector for the applicable KS.
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An improper torque value on the sensor will provide erroneous information to the ECM and a damaged sensor lead requires replacement of the sensor.
Step | Action | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | |||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |||||||||
|
Important: Start the engine, turn OFF the A/C. If an engine knock can be heard, repair the engine mechanical problem before proceeding with this diagnostic. Refer to Symptoms - Engine Mechanical in Engine Mechanical-3.0L (L81).
Did the DTC fail this ignition? | Go to Step 3 | Go to Diagnostic Aids | |||||||||
Does the DMM display a fluctuating frequency? | Go to Step 4 | Go to Step 7 | |||||||||
Does the DMM display a fluctuating frequency? | Go to Step 9 | Go to Step 5 | |||||||||
Test for the following conditions between the ECM connector and the KS harness connector:
Did you find and correct the condition? | Go to Step 11 | Go to Step 6 | |||||||||
6 | Test for poor connections or terminal tension at the knock sensor connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 11 | Go to Step 7 | ||||||||
Inspect for the KS for proper torque and for a damaged sensor lead. Did you find and correct the condition? | Go to Step 11 | Go to Step 8 | |||||||||
8 | Replace the knock sensor. Refer to Knock Sensor 1 Replacement or Knock Sensor 2 Replacement . Did you complete the replacement? | Go to Step 11 | -- | ||||||||
9 | Test for poor connections or terminal tension at the ECM connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 11 | Go to Step 10 | ||||||||
10 |
Important:
Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the action? | Go to Step 11 | -- | ||||||||
11 |
Does the DTC run and pass? | Go to Step 12 | Go to Step 2 | ||||||||
12 | With a scan tool, observe the stored information in Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | System OK | |||||||||
