VSS

lkovacs

Not-quite-so-new-guy
Dec 4, 2020
24
3
What exactly is the purpose of the Vehicle Speed Sensor in regards to an Oldsmobile 307? What does the ECM need the speed reading for?
 

L92 OLDS

Comic Book Super Hero
Mar 30, 2012
2,645
113
West Michigan
What exactly is the purpose of the Vehicle Speed Sensor in regards to an Oldsmobile 307? What does the ECM need the speed reading for?
I don’t think the ECM uses the signal. It is likely just for cruise control. Unlike modern vehicles the actual sensor is on the cluster and is wired to a signal conditioner usually found in a teal plastic enclosure.
 
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69hurstolds

Geezer
Supporting Member
Jan 2, 2006
5,647
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Yes, it does do the cruise as mentioned, but also, the ECM uses the VSS signal to get what the vehicle speed is, so as to manipulate anything that's speed sensitive, like the TCC solenoid.

It doesn't care if you're in park or neutral, but once the drive wheels start turning, it grounds CKT 437 and will throw a Code 24 if your stuff's out of whack. Like a broken speedo or broke speedo cable. (CSM says to disregard any Code 24 set if the drive wheels are not turning.)

There's a little wheel in the speedo head that "cuts" the little light beam from that VSS buffer piece. This "tells" the system what the vehicle speed is in pulses and the ECM calculates the time in-between pulses to figure out how fast the car is going in MPH.
 
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lkovacs

Not-quite-so-new-guy
Thread starter
Dec 4, 2020
24
3
Yes, it does do the cruise as mentioned, but also, the ECM uses the VSS signal to get what the vehicle speed is, so as to manipulate anything that's speed sensitive, like the TCC solenoid.

It doesn't care if you're in park or neutral, but once the drive wheels start turning, it grounds CKT 437 and will throw a Code 24 if your stuff's out of whack. Like a broken speedo or broke speedo cable. (CSM says to disregard any Code 24 set if the drive wheels are not turning.)

There's a little wheel in the speedo head that "cuts" the little light beam from that VSS buffer piece. This "tells" the system what the vehicle speed is in pulses and the ECM calculates the time in-between pulses to figure out how fast the car is going in MPH.
Yes, it does do the cruise as mentioned, but also, the ECM uses the VSS signal to get what the vehicle speed is, so as to manipulate anything that's speed sensitive, like the TCC solenoid.

It doesn't care if you're in park or neutral, but once the drive wheels start turning, it grounds CKT 437 and will throw a Code 24 if your stuff's out of whack. Like a broken speedo or broke speedo cable. (CSM says to disregard any Code 24 set if the drive wheels are not turning.)

There's a little wheel in the speedo head that "cuts" the little light beam from that VSS buffer piece. This "tells" the system what the vehicle speed is in pulses and the ECM calculates the time in-between pulses to figure out how fast the car is going in MPH.
Ah okay. Yeah I was just wondering what the reading is used for because I know it’s not connected, but the check engine light (I know the code is for the VSS, I checked. No other codes) doesn’t come on until I hit 60+ mph. Just curious why that was because you’d think it would trigger as soon as you started driving. So I was thinking maybe there is some process that happens when you hit 60 that the computer needs the VSS signal for and when it couldn’t get a reading the computer was like “!?!”
 

oldsmobile joe

Royal Smart Person
Nov 12, 2015
1,757
113
mpls
ecm needs vss for egr control, timing control, and tcc control.
 
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