BNR34 alternative reference for power steering pressure switch 49761-86L00 ?

[bigboss59400]

Hi,

Since the power steering pressure switch 49761-86L00 is not available.

I'm looking for alternative reference ? or if someone knows the spec of the switch ? (opening and/or closing at xx psi ?)

Thanks

[joshuaho96]

Looks like 49761-V5400 might fit but you would need to make an adapter harness.

[bigboss59400]

I thought about that one, however I don't know if the thread is the same ?

 

I believe this sensor tells the ECU when the power steering pump is working (especially for iddle)

Looking into r34 gtr and gtt service manual :

- when steering wheel is not turned : 4.6-4.7V meaning switch open

- when it is : 0V meaning switch closed

[GTSBoy]

1 hour ago, bigboss59400 said:

when steering wheel is not turned : 4.6-4.7V meaning switch open

- when it is : 0V meaning switch closed

Uh.... more likely to be the other way around. But whatever.

[bigboss59400]

On 7/16/2024 at 10:50 AM, GTSBoy said:

Uh.... more likely to be the other way around. But whatever.

 

[GTSBoy]

2 hours ago, bigboss59400 said:

 

No, by "the other way around", I meant 4.7V likely to correspond to switch closed, rather than open. You don't get voltage back to the control unit when a switch is open. You will definitely measure a voltage at one of the terminals of a switch when it is open, but it doesn't turn up at the other terminal (and hence then on to the ECU in this case) until it is no longer open.

 

[bigboss59400]

Except if I didn't understand, I'm sorry but I think you are wrong (no offense)

[joshuaho96]

On 7/16/2024 at 12:50 AM, bigboss59400 said:

I thought about that one, however I don't know if the thread is the same ?

 

I believe this sensor tells the ECU when the power steering pump is working (especially for iddle)

Looking into r34 gtr and gtt service manual :

- when steering wheel is not turned : 4.6-4.7V meaning switch open

- when it is : 0V meaning switch closed

It is for idle up signaling when the power steering is under high load. For example if the car is stopped and you turn the steering wheel all the way to the end of travel. My best guess is the thread is identical but unless you can measure yourself it’s hard to be sure. The R32 switch is generic for Nissan so you might be able to find one in a junkyard or a cheap aftermarket alibaba special just to check fitment. Then buy OEM new for actual road use. I’m unclear on whether the R33/34 need the clearance on the switch hence the special part requirement. 

 

10 hours ago, GTSBoy said:

No, by "the other way around", I meant 4.7V likely to correspond to switch closed, rather than open. You don't get voltage back to the control unit when a switch is open. You will definitely measure a voltage at one of the terminals of a switch when it is open, but it doesn't turn up at the other terminal (and hence then on to the ECU in this case) until it is no longer open.

 

I’m pretty sure 4.7V corresponding to open switch is normal. The ECU can detect it too, voltage can exist in the absence of current flow. When the switch closes as the impedance is very low relative to the voltage source it drops to near 0V which can also be sensed. 

[GTSBoy]

Yeah, but that's not normal usage of digital input power to any control system. A switch shorting directly to earth can only pull down the supply side to "zero" volts if there is an extremely high resistance as part of the supply side - effectively a limitation to a tiny current. Otherwise it's a dead short that will just flow as much current as it can.

Normally, as in a PLC digital input card (and indeed, most DIs on most other Nissan ECUs), you will have 12v or 5v available at a terminal on the ECU (or maybe even from elsewhere). That goes out to the switch and only comes back to another terminal on the DI (and this terminal is the actual digital input, the other one is effectively just the supply). With the switch open, no voltage turns up at the DI. With the switch closed, the voltage turns up at the DI. And such inputs are also high impedance to limit current flow to almost nothing. But this is a lot easier to do on the sensing side than it is on the supply side.

I'm quite surprised to see Nissan do what they've done on the R34.

[TurboTapin]

3 hours ago, GTSBoy said:

Yeah, but that's not normal usage of digital input power to any control system. A switch shorting directly to earth can only pull down the supply side to "zero" volts if there is an extremely high resistance as part of the supply side - effectively a limitation to a tiny current. Otherwise it's a dead short that will just flow as much current as it can.

Normally, as in a PLC digital input card (and indeed, most DIs on most other Nissan ECUs), you will have 12v or 5v available at a terminal on the ECU (or maybe even from elsewhere). That goes out to the switch and only comes back to another terminal on the DI (and this terminal is the actual digital input, the other one is effectively just the supply). With the switch open, no voltage turns up at the DI. With the switch closed, the voltage turns up at the DI. And such inputs are also high impedance to limit current flow to almost nothing. But this is a lot easier to do on the sensing side than it is on the supply side.

I'm quite surprised to see Nissan do what they've done on the R34.

On PLC inputs, yes 95% of the time you're sourcing. In automotive, including Nissan's, 95% of DI's are actually sinking. OP is correct. You sink inputs to GND, thus you will have 0VDC with the switch closed. 

Edited July 19, 2024 by TurboTapin

[joshuaho96]

7 hours ago, GTSBoy said:

Yeah, but that's not normal usage of digital input power to any control system. A switch shorting directly to earth can only pull down the supply side to "zero" volts if there is an extremely high resistance as part of the supply side - effectively a limitation to a tiny current. Otherwise it's a dead short that will just flow as much current as it can.

Normally, as in a PLC digital input card (and indeed, most DIs on most other Nissan ECUs), you will have 12v or 5v available at a terminal on the ECU (or maybe even from elsewhere). That goes out to the switch and only comes back to another terminal on the DI (and this terminal is the actual digital input, the other one is effectively just the supply). With the switch open, no voltage turns up at the DI. With the switch closed, the voltage turns up at the DI. And such inputs are also high impedance to limit current flow to almost nothing. But this is a lot easier to do on the sensing side than it is on the supply side.

I'm quite surprised to see Nissan do what they've done on the R34.

There's a lot of things that are weird on the R-chassis wiring/circuit design. Link highlights all the time how parts of the AC control system are always connected to +12V which can cause weird interactions that cause their ECU to brown out and cause no-starts in circumstances that it shouldn't. Nothing obscene, but just a little funny and no longer considered best practice.

[GTSBoy]

Bah! I just went and had a look. Pretty much all of the switches that I would have expected to be externally sourced and sunk at the ECU (on R32, such as TPS, neutral switch, etc) were ECU sourced. And now I have to wonder what sort of drugs the automotive engineering world have been taking.

[TurboTapin]

16 hours ago, GTSBoy said:

Bah! I just went and had a look. Pretty much all of the switches that I would have expected to be externally sourced and sunk at the ECU (on R32, such as TPS, neutral switch, etc) were ECU sourced. And now I have to wonder what sort of drugs the automotive engineering world have been taking.

There's advantages and disadvantages to both. Sourced DI's are used in automotive for reliability (You can't short signal wires) and ease of use (You have chassis GND available to you anywhere).