Circuit Description
The DTC P0325 Knock Sensor (KS) Circuit diagnostic monitors the activity on the knock sensor circuit. The KS is non-resonant design that is constructed of a piezoelectric element which generates an AC signal when vibrated. Normal engine operation will cause the KS to generate signals of known frequencies. When engine knock is present, the KS frequency changes. This signals the powertrain control module (PCM) to retard ignition timing. The PCM sends a bias voltage of 5 volts to the KS on the KS Signal High circuit. The PCM expects approximately 2.5 volts back on the KS Signal Low circuit. The KS generated AC signal rides on top of the bias voltage provided by the PCM. For additional information on the operation of the KS refer to Knock Sensor (KS) System Description .
Conditions for Running the DTC
| • | First condition--the engine running |
| • | Second condition--the vehicle speed sensor (VSS) and the throttle position (TP) sensor indicate that the vehicle is accelerating with the engine speed more than 2,000 RPM |
Conditions for Setting the DTC
| • | First condition--there is no bias voltage detected on the KS signal circuit |
| • | Second condition--no change is detected in the KS signal for more than 20 seconds |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | The PCM stores the conditions that were present when the DTC set as Freeze Frame data. |
| • | The PCM enters the Fail-Safe function and defaults to maximum spark retard values. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present. |
| • | The DTC clears after 40 consecutive warm-up cycles have occurred without a fault. |
| • | A DTC can be cleared by using the scan tool Clear DTC Information function. |
Diagnostic Aids
Inspect for the following conditions:
| • | A loose KS can cause a loss of the KS signal. Check the KS for proper torque. The correct KS sensor torque is 39 N·m (29 lb ft). |
| • | Engine acceleration will be compromised and AT downshifts delayed when operating in the Fail-safe mode. |
| • | If a DTC P0325 sets while the engine is idling, inspect for a loose connection at the PCM or KS. |
An intermittent malfunction may be caused by a fault in the KS sensor electrical circuit. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions .
The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions present when the DTC first set.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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This step verifies whether the DTC P0325 is the result of a hard failure or an intermittent condition. Operating the vehicle in Check Mode enhances the diagnostic capabilities of the PCM.
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This step verifies the resistance of the KS.
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This step verifies the knock sensors ability to output the correct frequency signal for a given engine speed.
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||||||
Is the voltage near the specified value? | 5.0 V | Go to Step 4 | Go to Step 3 | |||||
3 | Measure the voltage from the KS Signal High circuit to a good ground with the DMM. Is the voltage near the specified value? | 5.0 V | Go to Step 7 | Go to Step 6 | ||||
Is the resistance near the specified value? | 200k ohms at 20°C (68°F) | Go to Step 5 | Go to Step 8 | |||||
Was the Hz frequency observed during both tests within the specified values? | 0.5-2.0 kHz 21.0-29.0 kHz | Go to Diagnostic Aids | Go to Step 8 | |||||
6 |
Did you find and repair a condition? | -- | Go to Step 12 | Go to Step 10 | ||||
7 |
Did you find and repair a condition? | -- | Go to Step 12 | Go to Step 10 | ||||
8 |
Did you find and repair a condition? | -- | Go to Step 12 | Go to Step 9 | ||||
9 | Replace the knock sensor. Refer to Knock Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||
10 |
Did you find and repair a condition? | -- | Go to Step 12 | Go to Step 11 | ||||
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 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||
