how to diagnose a bad knock sensor/circuit
Thread Starter
Joined: Nov 2001
Posts: 10,018
Likes: 51
From: Virginia
how to diagnose a bad knock sensor/circuit anybody know anything i can measure with a voltmeter such as proper off and on resistance etc. for the sensors to show good or bad?
the circuit i can check with a continuity test.
what are symptoms of a bad knock sensor other than throwing one of the 3 codes.??
does a bad knock sensor get noticed by the computer and therefore 4* is pulled automatically at all wot occurences?
thats what mine is doing.. i had 26 total with 4* knock and 14 total still with 4* knock. (2 different setups)
if something was screwed up in the engine/tuning then the knock would go away when i backed down the timing, which it didnt.
Thanks, DAve
the circuit i can check with a continuity test.
what are symptoms of a bad knock sensor other than throwing one of the 3 codes.??
does a bad knock sensor get noticed by the computer and therefore 4* is pulled automatically at all wot occurences?
thats what mine is doing.. i had 26 total with 4* knock and 14 total still with 4* knock. (2 different setups)
if something was screwed up in the engine/tuning then the knock would go away when i backed down the timing, which it didnt.
Thanks, DAve
TECH Resident
Joined: Jan 2002
Posts: 754
Likes: 0
From: USA
Re: how to diagnose a bad knock sensor/circuit The resistor in the knock sensor is between 93 and 104K ohm if is working correctly.
Measure across each sensors wire and ground with VTOM ( disconnected from connector going to PCM)
If you bang on the engine to induce knock the sensor then produces low AC voltage as long as it is getting the DC voltage from PCM.
The rear knock seems to fail more often the the front one as to the ones I have replaced.
Also washing engine, or any water getting onto engine valley could run down the recess where sensor is and waste the sensor.
GM TSB calls for a dam made around sensor to prevent future water seeping into sensor.
<small>[ July 19, 2002, 08:51 PM: Message edited by: Team ZR-1 ]</small>
Measure across each sensors wire and ground with VTOM ( disconnected from connector going to PCM)
If you bang on the engine to induce knock the sensor then produces low AC voltage as long as it is getting the DC voltage from PCM.
The rear knock seems to fail more often the the front one as to the ones I have replaced.
Also washing engine, or any water getting onto engine valley could run down the recess where sensor is and waste the sensor.
GM TSB calls for a dam made around sensor to prevent future water seeping into sensor.
<small>[ July 19, 2002, 08:51 PM: Message edited by: Team ZR-1 ]</small>
Thread Starter
Joined: Nov 2001
Posts: 10,018
Likes: 51
From: Virginia
Re: how to diagnose a bad knock sensor/circuit ok heres what i got so far, i did this with the intake and everything on just tapping into the computer harness (ignition on or off) and measuring the wire with respect to engine ground.
pin 30 spark retard signal off: 6.09kohm on: 0 resistance (connected str8 to ground)
pin 68 knock sensor rear off: 4.61kohm on:5.72kohm
pin 69 knock sensor front off: 4.62kohm on: 5.74kohm
pin 68 key on voltage to ground 30.5mv
pin 69 key on voltage to ground 30.0mv
does any of this say anything or will i really have to pull the intake to find a good reading value?
pin 30 spark retard signal off: 6.09kohm on: 0 resistance (connected str8 to ground)
pin 68 knock sensor rear off: 4.61kohm on:5.72kohm
pin 69 knock sensor front off: 4.62kohm on: 5.74kohm
pin 68 key on voltage to ground 30.5mv
pin 69 key on voltage to ground 30.0mv
does any of this say anything or will i really have to pull the intake to find a good reading value?
Thread Starter
Joined: Nov 2001
Posts: 10,018
Likes: 51
From: Virginia
Re: how to diagnose a bad knock sensor/circuit removed the intake, checked both sensors, are at 100kohm on the nose, checked the wires and everything is ok, put the car back together and got the 332 code again. im going to replace the rear sensor with a resistor next and see what happens.
