Knock Sensor Operation
See IGNITION SYSTEM .
DESCRIPTION
All vehicles are equipped with a high energy ignition system capable of producing in excess of 40,000 volts. Systems include the C 3 I system, DIS system and IDI system. Catera uses a simple DIS system which contains a coil pack which is directly controlled by the ECM. Camaro, Firebird and Corvette use a multiple-coil ignition system which utilizes 8 separate ignition coil/module assemblies mounted on the rocker covers. This system is also known as Coil-Near-Plug (CNP).
In conjunction with the ignition system, a knock sensor retard system is used. System consists of a knock sensor, knock sensor module (if equipped) and PCM. When detonation (engine knock) occurs, knock sensor produces a low voltage AC signal. This signal inputs to the PROM or knock sensor module (if equipped) located internal of PCM.
PCM supplies a 5-volt DC reference signal on the knock sensor signal line. Internal circuitry of the knock sensor will pull this voltage down to about 2.5 volts. When detonation (engine knock) occurs, the knock sensor produces an AC voltage signal which rides on the 2.5-volt DC signal back to the knock sensor module or PCM. The voltage and frequency of this signal depends upon knock signals received by the knock sensor. The PCM will retard ignition control timing until signals from knock sensor cease.
Failure in knock sensor circuit should set a related diagnostic trouble code. If a related diagnostic trouble code is not present and the knock sensor system is suspected as the cause of a driveability problem, perform a functional check of the knock sensor. See appropriate SYSTEM & COMPONENT TESTING article.
The PCM is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction occurs, PCM will illuminate the Malfunction Indicator Light (MIL) located on instrument cluster. When a malfunction is detected and MIL is turned on, a corresponding Diagnostic Trouble Code (DTC) will be stored in PCM memory. Malfunctions are designated as either "emission related" or as "non-emission related", and are divided into 4 code types to identify type of fault. The 4 code types are defined as follows
- Type "A" Emission related faults that illuminate MIL at first occurrence of a fail condition.
- Type "B" Emission related faults that illuminate MIL if a fault occurs in 2 consecutive ignition cycles.
- Type "C" Non-emission related faults that illuminate MIL only when fault is present. MIL will turn off 3 seconds after engine start if fault is no longer present, but a record of fault will remain stored in memory.
- Type "D" Non-emission related faults which do not illuminate MIL.
Emission related DTCs (type "A" or "B") cause MIL to illuminate and remain on until the malfunction is repaired. On models using digital display on dash to indicate codes, codes may be accompanied by a "current" or "history" indication for intermittent and hard failures. If MIL illuminates and remains on during vehicle operation, cause of malfunction must be determined using affected Diagnostic Trouble Code (DTC) located in appropriate SELF-DIAGNOSTICS article. If a sensor fails, PCM will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional but loss of good driveability is likely.
Non-emission related DTCs (type "C") cause MIL to flicker or glow and go out about 10 seconds after the intermittent fault goes away. The corresponding diagnostic trouble code, however, will be retained in PCM memory. On models using a digital display on dash to indicate codes, codes may be accompanied by a "current" or "history" indication for intermittent and hard failures. If related fault does not reoccur within 50 engine restarts, related diagnostic trouble code will be erased from PCM memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See appropriate TROUBLE SHOOTING - NO CODES article.