RB25 Knock Sensor question - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

96Turbo · 05-26-2009, 04:59 PM

I need some help/advice diagnosing the knock sensor system on my RB25.

I've got the FSM and to check the sensors it says to check the voltage between the plug on the ECU & ground. It should be approximately 4V for a good sensor.

One sensor I replaced with a used one (broke the stock one), and the other is original.

The replacement reads about 2.5V....while the other plug reads 0V. I know the wiring is good (no breaks...)

The sensor that reads 0V...do you think it could be the sensor that's bad? Possibly the ECU? It seems like there should be SOME kind of voltage across that terminal. I've heard of people checking the resistance values of the sensors to see if they're within spec, but my FSM doesn't show anything like that. Only the voltage check.

What do you guys think? Bad ECU or bad sensor(s)

GSXRJJordan · 05-26-2009, 05:49 PM

If the ECU is on/powered, and that sensor isn't showing any voltage, you most likely have a wiring problem. I'm trying to look through my notes to see if they both connect to the same power wire, but worst case, just hook the second sensor into the first's power lead. Shouldn't pwn the ECU.

If there's continuity between the +12V and ground leads of the sensor, though, might be a bad sensor.

eh? · 05-26-2009, 06:06 PM

It's a single wire sensor, no power/ground.

Is the ecu faulting the sensors?
You can try ohming out the sensors, it usually reads around 500k ohms.
But its very common of the connector socket to be pushed back and that can cause the ecu to throw a code.

96Turbo · 05-26-2009, 08:01 PM

How does one go about "ohming out the sensors" when i try reading the resistance from the single pin on the sensor across the body of the sensor i get discontinuity (inf. resistance) How does the ECU fault the sensors? I unplugged the subharness and checked the voltage across each pin and got about 4.85V for each. This would lead me to believe that the ECU is good since there is no discrepancy between the two. I took apart my subharness though, I think there might have been some of the shielding wire digging into the sensor wire. I'm about to plug it back in and check. I'll letcha know thanks for the help so far

GSXRJJordan · 05-26-2009, 09:08 PM

Quote:

Originally Posted by 96Turbo

How does one go about "ohming out the sensors" when i try reading the resistance from the single pin on the sensor across the body of the sensor i get discontinuity (inf. resistance) How does the ECU fault the sensors? I unplugged the subharness and checked the voltage across each pin and got about 4.85V for each. This would lead me to believe that the ECU is good since there is no discrepancy between the two. I took apart my subharness though, I think there might have been some of the shielding wire digging into the sensor wire. I'm about to plug it back in and check. I'll letcha know thanks for the help so far

I'm with ya that the ECU isn't the problem - rarely is, unless it's a S2 RB25/igniter issue, or a MAF short.

If there's no continuity between the sensor and the ground, you should see voltage on that pin. I'm interested now lol... keep us updated.

eh? · 05-26-2009, 10:22 PM

What happened that caused you to check the sensors?

96Turbo · 05-26-2009, 10:43 PM

code 34...

and i still haven't gotten around to plugging everything back in and trying again. Like i said, i think that maybe some of the shielding might have been making contact with the sensor wire which would definitely cause problems...

but how do you check the resistance of the sensor? I've got 3 of them and i get discontinuity between the single plug in the middle & the body of the plug on all of them...

eh? · 05-26-2009, 11:32 PM

What kind of meter do you have? It should read 500K ohms from the pin to body.

GSXRJJordan · 05-26-2009, 11:39 PM

Yeah I think he's using the continuity tester (not an actual resistance reading) on the multimeter. Change it to 1M ohms, and you should see '.5'.

96Turbo · 05-27-2009, 12:45 PM

I was using the resistance reading on my MM, but in the wrong range. I tried it on the 200k setting and wasn't getting anything. But once I put it on the 20M setting I got .56, .57, and .8 something for the 3 sensors. (.8 and .57 for the ones that are actually on the engine as the other one has a broken plug).

But I think it might have just been some bad wiring and the ground shielding was shorting it out. I just put everything back together and drove it to the end of my street and back and I'm getting code 55.

I'm gonna go take it for a serious test run right now. I'll let you know how it goes

eh? · 05-27-2009, 02:41 PM

Check the sockets and make sure it's seated right. The KS connector sucks and the socket can push back over time.

GSXRJJordan · 05-27-2009, 03:31 PM

Quote:

Originally Posted by 96Turbo

I was using the resistance reading on my MM, but in the wrong range. I tried it on the 200k setting and wasn't getting anything. But once I put it on the 20M setting I got .56, .57, and .8 something for the 3 sensors. (.8 and .57 for the ones that are actually on the engine as the other one has a broken plug).

But I think it might have just been some bad wiring and the ground shielding was shorting it out. I just put everything back together and drove it to the end of my street and back and I'm getting code 55.

I'm gonna go take it for a serious test run right now. I'll let you know how it goes

W00t, glad you got it sorted

96Turbo · 05-27-2009, 07:32 PM

well the engine runs great...but now that it's making decent power my clutch isn't too happy about it...

05-26-2009, 04:59 PM	#1
96Turbo Zilvia FREAK! Join Date: Nov 2007 Location: AZ Age: 32 Posts: 1,315 Trader Rating: (11) Feedback Score: 11 reviews	RB25 Knock Sensor question I need some help/advice diagnosing the knock sensor system on my RB25. I've got the FSM and to check the sensors it says to check the voltage between the plug on the ECU & ground. It should be approximately 4V for a good sensor. One sensor I replaced with a used one (broke the stock one), and the other is original. The replacement reads about 2.5V....while the other plug reads 0V. I know the wiring is good (no breaks...) The sensor that reads 0V...do you think it could be the sensor that's bad? Possibly the ECU? It seems like there should be SOME kind of voltage across that terminal. I've heard of people checking the resistance values of the sensors to see if they're within spec, but my FSM doesn't show anything like that. Only the voltage check. What do you guys think? Bad ECU or bad sensor(s)

05-26-2009, 05:49 PM	#2
GSXRJJordan Post Whore! Join Date: May 2006 Location: << 626 >> Posts: 9,135 Trader Rating: (19) Rides Gallery: GSXRJJordan Feedback Score: 19 reviews	If the ECU is on/powered, and that sensor isn't showing any voltage, you most likely have a wiring problem. I'm trying to look through my notes to see if they both connect to the same power wire, but worst case, just hook the second sensor into the first's power lead. Shouldn't pwn the ECU. If there's continuity between the +12V and ground leads of the sensor, though, might be a bad sensor. __________________ Jordan Innovations has a new web site! www.JordanInnovations.com -- All your favorite FD Pro Drifters love it, trust me -- www.JordanInnovations.com

05-26-2009, 11:39 PM	#9
GSXRJJordan Post Whore! Join Date: May 2006 Location: << 626 >> Posts: 9,135 Trader Rating: (19) Rides Gallery: GSXRJJordan Feedback Score: 19 reviews	Yeah I think he's using the continuity tester (not an actual resistance reading) on the multimeter. Change it to 1M ohms, and you should see '.5'. __________________ Jordan Innovations has a new web site! www.JordanInnovations.com -- All your favorite FD Pro Drifters love it, trust me -- www.JordanInnovations.com

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05-26-2009, 06:06 PM	#3
eh? Zilvia Member Join Date: Apr 2005 Location: Orlando, FL Age: 40 Posts: 283 Trader Rating: (0) Feedback Score: 0 reviews	It's a single wire sensor, no power/ground. Is the ecu faulting the sensors? You can try ohming out the sensors, it usually reads around 500k ohms. But its very common of the connector socket to be pushed back and that can cause the ecu to throw a code.

05-26-2009, 08:01 PM	#4
96Turbo Zilvia FREAK! Join Date: Nov 2007 Location: AZ Age: 32 Posts: 1,315 Trader Rating: (11) Feedback Score: 11 reviews	How does one go about "ohming out the sensors" when i try reading the resistance from the single pin on the sensor across the body of the sensor i get discontinuity (inf. resistance) How does the ECU fault the sensors? I unplugged the subharness and checked the voltage across each pin and got about 4.85V for each. This would lead me to believe that the ECU is good since there is no discrepancy between the two. I took apart my subharness though, I think there might have been some of the shielding wire digging into the sensor wire. I'm about to plug it back in and check. I'll letcha know thanks for the help so far

05-26-2009, 10:22 PM	#6
eh? Zilvia Member Join Date: Apr 2005 Location: Orlando, FL Age: 40 Posts: 283 Trader Rating: (0) Feedback Score: 0 reviews	What happened that caused you to check the sensors?

05-26-2009, 10:43 PM	#7
96Turbo Zilvia FREAK! Join Date: Nov 2007 Location: AZ Age: 32 Posts: 1,315 Trader Rating: (11) Feedback Score: 11 reviews	code 34... and i still haven't gotten around to plugging everything back in and trying again. Like i said, i think that maybe some of the shielding might have been making contact with the sensor wire which would definitely cause problems... but how do you check the resistance of the sensor? I've got 3 of them and i get discontinuity between the single plug in the middle & the body of the plug on all of them...

05-26-2009, 11:32 PM	#8
eh? Zilvia Member Join Date: Apr 2005 Location: Orlando, FL Age: 40 Posts: 283 Trader Rating: (0) Feedback Score: 0 reviews	What kind of meter do you have? It should read 500K ohms from the pin to body.

05-27-2009, 12:45 PM	#10
96Turbo Zilvia FREAK! Join Date: Nov 2007 Location: AZ Age: 32 Posts: 1,315 Trader Rating: (11) Feedback Score: 11 reviews	I was using the resistance reading on my MM, but in the wrong range. I tried it on the 200k setting and wasn't getting anything. But once I put it on the 20M setting I got .56, .57, and .8 something for the 3 sensors. (.8 and .57 for the ones that are actually on the engine as the other one has a broken plug). But I think it might have just been some bad wiring and the ground shielding was shorting it out. I just put everything back together and drove it to the end of my street and back and I'm getting code 55. I'm gonna go take it for a serious test run right now. I'll let you know how it goes

05-27-2009, 02:41 PM	#11
eh? Zilvia Member Join Date: Apr 2005 Location: Orlando, FL Age: 40 Posts: 283 Trader Rating: (0) Feedback Score: 0 reviews	Check the sockets and make sure it's seated right. The KS connector sucks and the socket can push back over time.

05-27-2009, 07:32 PM	#13
96Turbo Zilvia FREAK! Join Date: Nov 2007 Location: AZ Age: 32 Posts: 1,315 Trader Rating: (11) Feedback Score: 11 reviews	well the engine runs great...but now that it's making decent power my clutch isn't too happy about it...