Circuit Description
The knock sensor (KS) system enables the powertrain control module (PCM) to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation. The KS produces an AC signal that varies at all engine speeds and loads. The PCM makes adjustments to the spark timing based on the amplitude and frequency of the KS signal. The PCM receives the KS signal through a signal circuit. The KS ground is supplied by the PCM through a low reference circuit. The PCM uses the KS to calculate the amount of normal engine noise, a noise channel, for a wide range of engine speeds and loads. The PCM compares the actual KS signal to the learned noise channel. The PCM uses the noise channel in order to diagnose the KS and the related wiring. If the PCM detects a loss of the noise channel, this DTC sets.
Conditions for Running the DTC
| • | The engine speed is more than 2,800 RPM. |
| • | The system voltage is more than 11 volts. |
Conditions for Setting the DTC
The PCM detects a KS signal that is out of the calibrated range.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | 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 emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
| • | Inspect the KS for proper installation. A KS that is loose or over torqued may cause a DTC to set. The KS should be free of thread sealant. The KS mounting surface should be free of burrs, casting flash, and foreign material. |
| • | For an intermittent condition, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step ensures the malfunction is present.
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This step ensures that the KS is capable of detecting detonation and producing a signal.
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If the KS signal circuit is shorted to ground or shorted to voltage, the KS may still produce a signal.
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If the KS low reference circuit is shorted to ground or shorted to voltage, the KS may still produce a signal.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | |||
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |
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Important: If an engine mechanical noise can be heard, repair the condition before proceeding with this diagnostic. Refer to Symptoms - Engine Mechanical in Engine Mechanical.
Does the DTC fail this ignition? | Go to Step 3 | Go to Intermittent Conditions | |
Does the DMM display a fluctuating frequency while tapping on the engine block? | Go to Step 6 | Go to Step 4 | |
4 | Test the KS signal circuit and the KS low reference circuit for an open or for a high resistance. Refer to Testing for Continuity in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 5 |
5 | Test the KS signal circuit for a short to the KS low reference circuit. Refer to Testing for Short to Ground in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 8 |
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Important: Disconnection of the PCM during testing may eliminate the voltage or ground source that caused this fault. Test the KS signal circuit for a short to ground or for a short to voltage. Refer to Testing for Short to Ground and Testing for a Short to Voltage in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 7 | |
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Important: Disconnection of the PCM during testing may eliminate the voltage or ground source that caused this fault. Test the KS low reference circuit for a short to ground or for a short to voltage. Refer to Testing for Short to Ground and Testing for a Short to Voltage in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 9 | |
8 | Test for an intermittent and for a poor connection at the KS/starter solenoid harness connector and at the KS. 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 12 | Go to Step 10 |
9 | Test for an intermittent and for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 11 |
10 | Replace the KS. Refer to Knock Sensor Replacement . Did you complete the replacement? | Go to Step 12 | -- |
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | Go to Step 12 | -- |
12 |
Does the DTC fail this ignition? | Go to Step 2 | Go to Step 13 |
13 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | System OK | |
