Purpose:
To control spark knock (detonation), a knock sensor (KS) system is used.
This system is designed to retard spark timing when excessive spark knock
is detected in the engine. The KS system allows the engine to use maximum
spark advance for optimal driveability and fuel economy under all operating
conditions.
Operation:
The powertrain control module (PCM) uses a knock sensor to detect abnormal
vibration in the engine (detonation/spark knock). Mounted on the engine block,
the knock sensor produces an AC voltage signal at all engine speeds
and loads. The PCM then adjusts the spark timing based on the amplitude
and frequency of the KS signal. The PCM uses the KS signal to calculate
an average voltage. Then, the PCM assigns a voltage range above and
below the average voltage value. The PCM checks the KS and related wiring
by comparing the actual knock signal to the assigned voltage range.
A normal KS signal should vary outside the assigned voltage range as
shown in the NORMAL KS figure. If the PCM detects a KS signal within
the assigned voltage range as shown in the ABNORMAL figure the applicable
diagnostic trouble code (DTC) will be set.
Normal Knock Sensor Signal
Abnormal Knock Sensor Signal
Legend
- Upper fail region
- Knock sensor calculated average
- Knock sensor signal
- Lower fail region
Diagnosis
A diagnostic trouble code (DTC) may set for the following conditions
or faults:
| • | The PCM malfunctions in a manner which will not allow the PCM
to run a diagnostic of the KS circuit. |
| • | The KS signal is within the assigned voltage range. |
| • | The KS signal is not present. |
| • | The PCM is unable to eliminate the knocking condition using the
maximum spark retard. |
