Circuit Description
The powertrain control module (PCM) monitors a knock sensor (KS) in order to determine if detonation is present. The KS produces an AC voltage at all engine speeds and loads. The powertrain control module (PCM) then adjusts the spark timing based on the amplitude and frequency of the KS signal. The PCM uses the KS signal to calculate the average voltage and then assigns a voltage range value. The PCM should monitor the KS signal within the assigned voltage range. This diagnostic trouble code (DTC) will set if the KS signal is outside the assigned voltage range or the KS signal is not present.
Conditions for Running the DTC
| • | DTCs P0117, P0118, P0122, P0123, or P0125 are not set. |
| • | The engine speed is between 2,000-3,000 RPM. |
| • | The engine run time is more than 10 seconds. |
| • | The engine coolant temperature (ECT) is more than 60°C (140°F). |
| • | The manifold absolute pressure (MAP) is less than 44 kPa. |
| • | The system voltage is more than 10 volts. |
Conditions for Setting the DTC
The PCM detects that the KS signal is outside the assigned voltage range or the KS signal is not present.
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 physical damage. A KS that is dropped or damaged may cause a DTC to set. |
| • | Inspect the KS for proper installation. A KS that is loose or over torqued may cause a DTC to set. The KS mounting surface must be free of burrs, casting flash, and foreign material. |
| • | The KS should be clear of hoses, brackets, and engine electrical wiring. |
| • | 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 tests the KS for proper operation.
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If the KS signal wire is shorted to ground or is shorted to voltage, the KS may still produce a signal.
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If the KS low reference is shorted to ground or is shorted to voltage, the KS may still produce a signal.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views | |||
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |
Important: If an engine knock can be heard, repair the engine mechanical condition before proceeding with this diagnostic. Refer to Symptoms - Engine Mechanical in Engine Mechanical - 4.3L. Does the DTC fail this ignition? | Go to Step 3 | Go to Diagnostic Aids | |
Important: Do not tap on plastic engine components. Does the DMM display a fluctuating frequency while tapping on the engine block? | Go to Step 6 | Go to Step 4 | |
4 |
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 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 |
Test the KS signal circuit for a short to ground and 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 | |
Test the KS low reference circuit for a short to ground and 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. 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 and Connector Repairs 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 | |
