1G Power Steering Pressure Switch

[miguelmcv]

I have search for a couple of days and can't find the Info that I am looking for, so I have don my work.

I want to know how many volts the switch delivers to the ECU.
I know it is an ON and OFF switch, and delivers ground to the ECU, But, (WHAT'S THE VOLTAGE).

I have read the manual several times, and it doesn't say anything about the volts.
It does say how to test it, But, It doesn't mention the volts that it uses.

Any one that has a very good knowledge about the Power Steering Sensor.

Or, any one that can measure the Volts in your car while is running and steering in action (turning wheels).

Any advice or any favor will be appreciated.

 

[Infamous33]

As you said, it is just a simple on/off switch to the ecu.
I would just pull the connector off and measure the voltage with the key on.
The ecu SENDS voltage to the switch at all times, it doesn't recieve any voltage, and the switch will ground the circuit when pressure input is sensed. There is an internal resistor in the ecu on this circuit so I would assume it to be either 12v or 5v. When turning the wheel, there will be zero volts showing on the wire.
L-W wire (purple/white trace ??) is the wire color, looks to be grounded thru the switch.
Not really sure where you are going with this tho.... My PS switch was unplugged for the first 3 years I had the car since the little tit was broken off the switch when I got it. It only bumps the idle about 50-100 rpm with input.

 

[miguelmcv]

As you said, it is just a simple on/off switch to the ecu.
I would just pull the connector off and measure the voltage with the key on.
The ecu sends voltage to the switch at all times and the switch will ground the circuit when pressure input is sensed. There is an internal resistor in the ecu on this circuit so I would assume it to be either 12v or 5v.
L-W wire (purple/white trace ??) is the wire color, looks to be grounded thru the switch.
Not really sure where you are going with this tho.... My PS switch was unplugged for the first 3 years I had the car since the little tit was broken off the switch when I got it. It only bumps the idle about 50-100 rpm with input.

Thanks for the input, but, I dont have the pump any more.
I am running an MR2 pump, so I need the exact volts to hook up the pump.
I wouldn't like to put a 12v and end up burning the ECU.

I am sure some one will jump in with the exact info..

Any ways, I do apreciate your help.

 

[arrowhead]

If is a simple on and off measure the voltage at ecu.

 

[Infamous33]

My PS switch was unplugged for the first 3 years I had the car since the little tit was broken off the switch when I got it. It only bumps the idle about 50-100 rpm with input.

If you leave the wire open, there will be little to no harm, as the increase in idle speed (which is only used at closed throttle) is sooo minimal would not affect anything. If you REALLY need the idle increase, what year MR2 is the pump from? I will look up the circuit and get back to you on how to fix it.

My point is..... the ECU sends the voltage, not the switch. There is a constant ground to the switch and until the input changes, the ECU sees nothing
If you apply power to the ECU on that wire, nothing will happen except for backfeeding power to a circuit that already has power applied to it.
The switch GROUNDS the power on the wire FROM the ecu.....
Does the car stall out when you turn the wheel at idle?

 

[miguelmcv]

If you REALLY need the idle increase, what year MR2 is the pump from? I will look up the circuit and get back to you on how to fix it.

My point is..... the ECU sends the voltage, not the switch. There is a constant ground to the switch and until the input changes, the ECU sees nothing
If you apply power to the ECU on that wire, nothing will happen except for backfeeding power to a circuit that already has power applied to it.
The switch GROUNDS the power on the wire FROM the ecu.....
Does the car stall out when you turn the wheel at idle?

My pump is from 91 to 95.

I have no problems with the pump system, not even my car stalls.

But, because I am running a 90amp Alternator, I was trying to help the Alternator when idling, So, I was trying to figure, on how to hook up the stock steering line to the MR2 pump system.

This way, The Car will raise up the APM when the pump turns ON.

 

[Infamous33]

I sorta follow you now. Looks to me, from the wiring schematics that you would want to splice your ps switch wire into the black/yellow wire in the 2 pin connector at the psecu.
That is the wire that the comp. grounds to turn on the pump, so it will automatically send a P/S pressure signal to your ECU and bump the idle.
May be a good idea to test that with a light connected to power first, but it seems to be how this works.

 

[miguelmcv]

I sorta follow you now. Looks to me, from the wiring schematics that you would want to splice your ps switch wire into the black/yellow wire in the 2 pin connector at the psecu.
That is the wire that the comp. grounds to turn on the pump, so it will automatically send a P/S pressure signal to your ECU and bump the idle.
May be a good idea to test that with a light connected to power first, but it seems to be how this works.

Yes, you are wright.

There are 2 wires at the PS ECU where I can hook up the switch line, But, 1 line delivers 4.5v (ground) or more when the engine is On, and delivers 1.5v (ground) or less when the engine is OFF.

The other line deliver 5v (ground) or more when the engine is ON, and it doesn't delivers anything when the engine is OFF (this could be the best line to hook up the switch line).

Now.,,,,,, What worries me is, If I hook up this wire and delivers a full 12v (ground), wouldn't it fry my ECU?.

This is why, I was trying to find out, how many volts the switch delivers.

If the Switch delivers 5v or something around, I can add a regulator to the line, to prevent the ECU from any damage.

Adding a regulator, will prevent the ECU from any damage and will get the wright signal.

Basically, What we need to know is.....

How many volts the Stock Power Steering switch delivers.

 

[Infamous33]

ok, hang on a minute. Stick with me on this...

The factory ps pressure switch is on/off, we have covered that enough.

What happens is the switch will pull the voltage that is fed from the ecu via a resistor (which prevents the ecu from shorting to ground, the resistor is the 'load' in the circuit)
The switch itself does not backfeed any power to the ecu. Imagine to take a light bulb, run one wire from the battery and hold the other in your hand. When you need to see (or the ecu needs to bump the idle up) you touch the other wire to ground. This doesn't burn up the battery because the light bulb uses the electricity before it gets back to ground.
That is how the ps switch works. There is a resistor inside the ecu that acts as a load to use up the voltage that is being sent down the wire.

Now on the mr2 setup, there is voltage being fed from the 80A fuse on the black wire, this splices to the motor AND to the ps driver when the relay is powered up. With the relay powered, and the 2 pin connector unplugged at the ps driver, you should have power on both wires. The power is waiting patiently for the bus to bring it back to Battery Town. Electricity will flow as far as it can, whenever it can. It you were to ground the Black/yellow wire, the pump would start to run even though it shows there are 12v on that wire.

The ps driver is the one that grounds that wire when it is told to by the ps ecu.
Therefore, it you splice into that wire, your ecu will see ps pressure whenever the driver turns on the ps motor.

Sorry for the wicked long post, just trying to help out and make things clear for you. Been doing this a looonnggg time and elect.is sort of a specialty for me.

 

[miguelmcv]

Them.......

Glad you jump in.

I didn't know how that Steering Switch line works.
All what I knew was that, it was an ON and OFF switch, But I always had on mind, that it delivers ground to the ECU...
Thanks to clarify that......

I can see what you are talking about.

But never in my mind cross that, the ECU had a resistor in that line (steering switch).

This makes everything easier then I expected.

So, basically, what you are saying is that, I just need to connect a line that delivers negative (ground) when the pump is ON, wright.

I have read the chemistry so, so, so many times, Before installing my pump.

How ever, Now that I have all that clear.

I will hook up the switch line to Negative (12v) from the pump system which it will be ground it only when the pump is active.

I will try to hook it up to the line that you all ready mention.

Thanks a ton to you brother.

 

[Infamous33]

miguel, PM sent !

Here is the '93 schematics

 

[miguelmcv]

Yeap,

That's the one.

The IDUP that connects to the Engine ecu (ps).

That's the only one that I don't know what it does.

I been looking and reading, But, no luck.

PM send.

I have a 91 schematic, But It doesn't say anything about that wirel