Knock Sensor Voltage Question
Knock Sensor Voltage Question So the knock sensor is basically a variable ground sensor with a 5 volt reference correct? Does anyone know the voltage drop to timing retard ratio?
Does 1 volt equal 4 degrees of retard? Any info would be great.
Thanks
Does 1 volt equal 4 degrees of retard? Any info would be great.
Thanks
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
It doesn't work like that.
It's a waveform type of signal (looks squigly) and the PCM filters it (elminates unwanted frequencies) to determine if knock is occuring, and then the PCM looks at the intensity/amplitude and retards accordingly.
It's a waveform type of signal (looks squigly) and the PCM filters it (elminates unwanted frequencies) to determine if knock is occuring, and then the PCM looks at the intensity/amplitude and retards accordingly.
TECH Enthusiast
Joined: Nov 2004
Posts: 600
Likes: 0
From: Coppell,TX
actually, straight from a manual.
Knock Sensor Operation
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.
basically it adds ac voltage to the dc line to show actual knock.
Knock Sensor Operation
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.
basically it adds ac voltage to the dc line to show actual knock.
Sounds like an AM transmitter. Well damn, I was hoping it was just a variable ground/voltage drop sensor so I could monitor it with my LM-1. Thanks for the info...I love this board.
Josh
Josh
