Circuit Description
The knock sensor (KS) system detects engine detonation. The PCM retards
the spark timing based on the signals from the knock sensors. The knock sensors
produce an AC voltage. The knock sensor voltages are an input to the
PCM. The amount of AC voltage produced is proportional to the amount
of knock.
An operating engine produces a normal amount of engine mechanical vibration
(noise). The knock sensors produce an AC voltage signal from this noise. When
an engine operates, the PCM learns the minimum and maximum frequency
of the noise the engine produces. When the PCM determines that this
frequency is less than or greater than the expected amount, a knock
sensor DTC will set.
Step
| Action
| Values
| Yes
| No
|
1
| Did you perform the Powertrain On-Board Diagnostic (OBD) System
Check?
| --
|
Go to Step 2
| Go to
Powertrain On Board Diagnostic (OBD) System Check
|
2
|
ImportantIf an engine knock can be heard, repair the engine mechanical condition
before proceeding with this diagnostic.
- Turn ON the ignition with the engine OFF.
- Review the Freeze Frame and/or Failure Records data for this DTC
and observe the parameters.
- Turn OFF the ignition for 15 seconds.
- Start the engine.
- Operate the vehicle within the conditions required for this diagnostic
to run, and as close to the conditions recorded in Freeze Frame and/or
Failure Records as possible. Special operating conditions
that you need to meet before the PCM will run this diagnostic,
where applicable, are listed in Conditions for Running
the DTC.
- Select the Diagnostic Trouble Code (DTC) option and the Specific
DTC option, then enter the DTC number with the scan tool.
Does the scan tool indicate that this diagnostic failed this ignition?
| --
|
Go to Step 3
| Go to Diagnostic Aids
|
3
|
- Disconnect the knock sensor electrical connector located behind
the intake manifold.
- Measure the resistance of the appropriate knock sensor by connecting
the DMM between the knock sensor signal circuit on the sensor side and
the engine block with the DMM .
- Set the DMM to the 400K ohm scale.
Is the resistance of the knock sensor within the specified range?
| 93-107Kohms
|
Go to Step 4
|
Go to Step 6
|
4
|
- Connect the DMM between the appropriate knock sensor signal circuit
on the sensor side and the engine block.
- Set the DMM to the AC voltage scale.
ImportantDo not tap on plastic engine components.
- Tap on the engine in the area of the appropriate knock sensor while
observing the signal indicated on the DMM .
Is any signal indicated on the DMM while tapping on the engine near
the Knock Sensor?
| --
|
Go to Step 5
|
Go to Step 7
|
5
|
- Disconnect the PCM connector C1 located on the same side as the
manufacturer's logo. Refer to
Powertrain Control Module (PCM) Replacement
.
- Test the KS signal circuit between the PCM and the knock sensor
connector for the following:
- An open
- A short to voltage
- A short to ground
- If you find a circuit condition, repair as necessary. Refer to
Wiring Repairs
in Wiring Systems.
Did you find and correct the condition?
| --
|
Go to Step 10
|
Go to Step
8
|
6
|
- Remove the intake manifold. Refer to
Intake Manifold Replacement
in Engine Mechanical 5.7L.
- Test for an open or a short to ground in the signal circuit between
the knock sensor jumper harness connector, located at the back of the
intake manifold, and the knock sensor connector. Refer to
Testing for Continuity
or
Testing for Short to Ground
in Wiring Systems.
- If a condition is located repair the circuit as necessary. Refer
to
Wiring Repairs
in Wiring
Systems.
Did you find and correct the condition?
| --
|
Go to Step 10
|
Go to Step
7
|
7
| Replace the Knock Sensor. Refer to
Knock Sensor (KS) Replacement
.
Is the action complete?
| --
|
Go to Step
10
| --
|
8
|
- Inspect the KS signal circuit for a poor connection at the
PCM. Refer to
Testing for Intermittent and Poor Connections
in Wiring Systems.
- If you find a poor connection repair the terminal as necessary.
Refer to
Repairing Connector Terminals
in Wiring Systems.
Did you find and correct the condition?
| --
|
Go to Step 10
|
Go to Step
9
|
9
|
ImportantProgram the replacement PCM.
Replace the PCM. Refer to
Powertrain Control Module (PCM) Replacement
.
Is the action complete?
| --
|
Go to Step
10
| --
|
10
|
- Select the Diagnostic Trouble Code (DTC) option and the Clear
DTC Information option with the scan tool.
- Start the engine and idle at the normal operating temperature.
- Select the Diagnostic Trouble Code (DTC) option and the Specific
DTC option, then enter the DTC number with the scan tool.
- Operate the vehicle within the conditions for running this DTC
as specified in the supporting text, if applicable.
Does the scan tool indicate that this test ran and passed?
| --
|
Go to Step 11
|
Go to Step
2
|
11
| Select the Capture Info option and the Review Info option with the
scan tool.
Does the scan tool display any DTCs that you have not diagnosed?
| --
| Go to the applicable
DTC table
| System OK
|