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Discussion Starter · #1 ·
Looking to hook up some electronics that call for tapping into the "vehicle speed sensor" looking for "pulses" 2p, 4p, 8p or 16 pulses. I know our Rs communicate the VSS over CAN but could I grab this raw info straight from one of the wheel speed sensors instead?
 

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Re: Does Vehicle speed sensor = wheel speed sensor? (juve021)

There is no specific VSS, it's computed by the BCM (brake control module) which monitors the four wheel sensors and transmits it on the CAN bus at regular intervals. The value is easily read by OBDII devices but not as an analog or pulsed raw signal.

You could theoretically tap into a single wheel, but you'll get many dozens of pulses per rotation, and you'd have to convert it to speed. Personally I wouldn't try it - the BCM might be confused and that would disable many critical functions.

Tom.
 

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Re: Does Vehicle speed sensor = wheel speed sensor? (juve021)

Hey guys, I remember reading about the AEM so I did a little digging. Sit down, here is everything you didn't ask for.


http://vccs.volvocars.se/acces...0.htm
and
http://vccs.volvocars.se/acces...9.htm

When you install a Volvo radio in combination with the accessory electronic module (AEM), extended functions can be obtained:
• Speed dependent volume
• Controlling display illumination (day/night position)
• Controlling symbol illumination strength
For further information on AEM, see Electronic accessory module, AEM


From VADIS:

"Signal for integrating an after market radio unit (tele-mute signal, speed signal, rheostat signal and controlled power supply to the external aerial amplifier)"

"The accessory electronic module (AEM) receives a speed signal (volume adaptation) via the CAN-net and brightness of the display lighting via rheostat from the central electronic module (CEM) (4/56)." and outputs them as analog signals for aftermarket HU's that suppport these features. FWIW, there is also a mute signal.

And here is the rest of the skinny:

Aftermarket radio unit

The design consists of a signal input and four signal outputs on the accessory electronic module (AEM).
The input signal is an analogue +12V mute signal, from either the reverse warning system or the non-integrated hands free system.
Two output signal are pulse width modulated signals for the lighting rheostat signal position and the speed sensitive volume signal.
One output signal is a digital 12V mute signal to the radio unit.
One output signal is a +30 supply for an external aerial amplifier.

When installing an after market radio unit, the car must be configured using new software. Configuration is carried out via VIDA.

The function is available as accessory for the accessory electronic module (AEM) for cars of later versions. (All S60's)
There are diagnostics for the system.


The v70 wiring diagram (the s60 should be the same for this circuit) shows a non CAN connection between the AEM and the HU (green wire/B7 connector on HU).
 

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Re: Does Vehicle speed sensor = wheel speed sensor? (juve021)

A little more from VADIS

Speed signal, value (Frozen value--stored when a diagnostic trouble code (DTC) is stored.)
Indicates a frequency based on the speed and wheel circumference using the formula: frequency = speed x 12/wheel circumference. The frequency signal is used to determine the volume of the radio.
The value is between 0-512 Hz.

Speed signal on AEM, B14 connection/green wire

Speed signal (radio), digital output signal

Ignition off
Activated Not Activated
Ubat Ubat

Ignition On
Activated Not Activated
PWM =30%-70% PWM =30%-70%

Pulse width modulation (PWM) signal
 

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Re: Does Vehicle speed sensor = wheel speed sensor? (MrTippy)

Okay, so now you need to find out what terminal the AEM provides this signal on, and we're done! Well, it will be necessary to convert the PWM to a straight analog signal.

Tom.
 

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Re: Does Vehicle speed sensor = wheel speed sensor? (tmtalpey)

Quote, originally posted by tmtalpey »
Okay, so now you need to find out what terminal the AEM provides this signal on,

B24 on the AEM or B7 on the HU (one of the green wires).
 

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Re: Does Vehicle speed sensor = wheel speed sensor? (juve021)

That's right, it is an accessory. Looks like it lists for about $140.

Yes there is software--although since it would be just reading the bus for your app, not sending anything (right?), might it not work for you without a d/l? I'll bet Tom or Jim know better about that.

You might be able to find one on a wreck (or get one from someone) that had parking assist (look for the sensors in the bumper; probably on lots of XC's) or maybe the upgraded alarm option. I doubt your friendly neighborhood salvage yard would even know what it is, hint, hint; except for maybe ErieVovo, who I'm sure would be happy to sell you one if they have it.

Something to think about then is Dietz. I recall seeing an online company selling a CAN black box adapter for the steering controls and I think they had one that does vehicle speed amongst other signals, but is probably no less $ and limited availability in the US.
 

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Discussion Starter · #10 ·
Re: Does Vehicle speed sensor = wheel speed sensor? (MrTippy)

Quote, originally posted by MrTippy »
That's right, it is an accessory. Looks like it lists for about $140.

Yes there is software--although since it would be just reading the bus for your app, not sending anything (right?), might it not work for you without a d/l? I'll bet Tom or Jim know better about that.

You might be able to find one on a wreck (or get one from someone) that had parking assist (look for the sensors in the bumper; probably on lots of XC's) or maybe the upgraded alarm option. I doubt your friendly neighborhood salvage yard would even know what it is, hint, hint; except for maybe ErieVovo, who I'm sure would be happy to sell you one if they have it.

Something to think about then is Dietz. I recall seeing an online company selling a CAN black box adapter for the steering controls and I think they had one that does vehicle speed amongst other signals, but is probably no less $ and limited availability in the US.

great thanks all.

so I've been reading the dietz manual and it states the speed sensor output is 0.64 Hz per km/h How do I know if this is compatible with 2p, 4p, 8p or 16 pulses?

at this point, it starting to seem that this is all a little bit too much work for what I need it for.

Modified by juve021 at 1:35 PM 3-15-2009
 

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Re: Does Vehicle speed sensor = wheel speed sensor? (MrTippy)

Quote, originally posted by MrTippy »

Yes there is software--although since it would be just reading the bus for your app, not sending anything (right?), might it not work for you without a d/l?

Correct, will not be recognized on the CAN w/o a DL.
Don't you just love Volvo for that! You can't even replace a front window switch anymore w/o a DL. http://********************/smile/emthdown.gif
 

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Re: Does Vehicle speed sensor = wheel speed sensor? (juve021)

Quote, originally posted by juve021 »
at this point, it starting to seem that this is all a little bit too much work for what I need it for.
What exactly are you thinking of doing with it? Installing an entire AEM just for a speed signal is silly, for sure, but there might be alternatives if we know what you need.

Tom.
 
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