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

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

Reply to
Tibur Waltson
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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.

Reply to
Steve T

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.

Reply to
Bob

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

Reply to
NissTech

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

Reply to
Tibur Waltson

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