Is my knock sensor dead from these readings? 97 Maxima Nissan

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Tibur Waltson - 12 Jun 2004 23:56 GMT

I've been plague by a "knock sensor" check engine light that won't
go away. I check the knock sensor while still bolted to the engine
block and got these readings at 2K-rpm:

DMM: ~20mV AC, 5.5M-Ohm.
Scope: ~20mV or ~ 30mV peak-to-peak when back-probe connector.
ECU to sensor supply power ~ 5VDC, when connected ~ 3.8VDC.

I remove the sensor from the engine block to test bench and
vibrate it to achieve this readings:

DMM: 76mV AC, 576K-Ohm.
Scope: 76mV peak-to-peak .

I reinstall the sensor into the vehicle and reset the ECU and no
improvements. Normal torque is about 50-lb? Has the sensor gone
bad/aged or the data retrieval technique is flawed?

Thanks

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Steve T - 13 Jun 2004 01:13 GMT

> I've been plague by a "knock sensor" check engine light that won't
> go away. I check the knock sensor while still bolted to the engine
[quoted text clipped - 13 lines]
> improvements. Normal torque is about 50-lb? Has the sensor gone
> bad/aged or the data retrieval technique is flawed?

Have you checked the readings at the ecu? Normally this light is caused my
corroded conections not a bad sensor, though I have had to replace a couple
of them.

Signature

Steve

http://www.atlantaracing.com

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Bob - 13 Jun 2004 04:31 GMT

>I've been plague by a "knock sensor" check engine light that won't
>go away. I check the knock sensor while still bolted to the engine
[quoted text clipped - 15 lines]
>
>Thanks

I've never seen a "run" spec but your cold test is on the money for
the resistance test. FWIW, lots and lots of people replace their knock
sensors on the Maxima.

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NissTech - 13 Jun 2004 12:05 GMT

The knock sensor in a non check engine light item, this means if the ECM
detects a fault with the KS it will not turn on the light for that problem
only.

my bet is you either have an O2 sensor code or an EVAP code along with the
KS

> I've been plague by a "knock sensor" check engine light that won't
> go away. I check the knock sensor while still bolted to the engine
[quoted text clipped - 15 lines]
>
> Thanks

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Tibur Waltson - 05 Jul 2004 14:22 GMT

> > I've been plague by a "knock sensor" check engine light that won't
> > go away. I check the knock sensor while still bolted to the engine
[quoted text clipped - 5 lines]
> > DMM: 76mV AC, 576K-Ohm.
> > Scope: 76mV peak-to-peak .

>"NissTech" <Haywood_Jablowme@msn.com> wrote
> The knock sensor in a non check engine light item, this means if the ECM
> detects a fault with the KS it will not turn on the light for that problem
> only, my bet is you either have an O2 sensor code or an EVAP code along with the
> KS

Thanks all. There was an O2 problem also.

All solved. Here's a KS comparison.

New knock sensor:
0.003 VAC with light tap using DMM
0.001 VAC w/ no tap
Resistance = 0.54 M-Ohm
Scope = Smooth curve AC sinewave

Old knock sensor:
0.033 VAC with light tap
0.001 VAC w/ no tap
Resistance = 5.49 M-Ohm
Scope = appears to be an AC sawhorse

Estimated torque on identical Bosch Japan sensor to
block = 15ft-lb. Bought from europartsdirect.com.

Tibur Waltson

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