Circuit Description
The powertrain control module (PCM) uses a knock sensor (KS) in order to detect engine detonation. The knock sensor produces an AC signal at all engine speeds, and loads. The PCM adjusts to the spark timing that is based on the amplitude and on the frequency of the KS signal.
The PCM uses the knock sensor in order to determine the amount of normal engine noise for a wide range of engine speeds and loads. The PCM compares the actual knock sensor signal to the learned noise channel. The PCM uses the noise channel in order to diagnose the knock sensor and the related wiring. If the PCM detects a loss of the noise channel, this diagnostic trouble code (DTC) will set.
Conditions for Running the DTC
| • | The engine speed is more than 3,000 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
If the conditions is intermittent, 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 wire is shorted to ground or shorted to voltage, the KS may still produce a signal.
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If the KS signal low reference is shorted to ground, or shorted to voltage, the KS may still produce a signal.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics | |||
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |
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Important: If an engine knock can be heard, repair the engine mechanical condition before proceeding with this diagnostic.
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 block? | Go to Step 7 | Go to Step 4 | |
4 | Test for an open in the knock sensor signal or low reference circuits. 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 signal circuit for a short to the low reference circuit Did you find and correct the condition? | Go to Step 12 | Go to Step 6 |
6 | Inspect for a poor connection at the knock sensor harness connector and at the knock sensor/starter solenoid harness connector. 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 10 |
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Important: Disconnection of the PCM during testing may eliminate the voltage or ground source that caused this fault. Test for a short to ground or a short to voltage in the KS signal circuit. 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 8 | |
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Important: Disconnection of the PCM during testing may eliminate the voltage or ground source that caused this fault. Test for a short to ground or short to voltage in the KS low reference circuit. 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 | |
9 | Inspect for a poor connection at the harness connector of 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 knock sensor. 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 run and pass? | Go to Step 13 | Go to Step 2 |
13 | Use the scan tool, in order to observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | System OK | |
