Cruise control

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ELCAM

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Jun 19, 2021
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When you say no resistance across B and D on the servo is it infinite resistance or zero?
 

ELCAM

Royal Smart Person
Jun 19, 2021
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Do you have an inductor function on your meter?

Sounds like the coil is open so your getting an infinite reading is my guess. Sounds like the servo is bad.
 
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69hurstolds

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Jan 2, 2006
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Sounds like the variable sensor throttle position coil wiring is broken (SPS). It's the feedback to the under-dash controller. With any of the coil wiring in the servo is broken or shorted, the servo and entire system will not work. Service manual says--- replace servo.

For the record, both solenoids operate independently to apply vacuum and vent the servo as needed. The servo is normally vented, and vacuum valve solenoid is normally closed. When energized, the vacuum valve opens to vacuum source but the vent valve energizes to close. These are the only places you should see voltage is when the system wants to operate. Since the car has to be above a certain mph to engage (around 25-30 mph), you should never see voltage to the servo at idle parked outside the garage. This is why they don't have you check the voltage at the servo because it would be extremely difficult to setup the car for those conditions. The controller box under the dash sends the signal output to the solenoids as needed based on the input variables and feedback from the servo position sensor (SPS) circuit. If the coils are good on resistance, it is generally expected the servo will work correctly.

Now, if you WERE able to hook up a voltmeter to your vacuum/vent solenoids circuit while driving, you should intermittently see voltage at terminals E (tan wire) for the vacuum solenoid and A (blue/white stripe wire) for the vent solenoid from the cruise module under the dash. There won't necessarily be power being sent to the solenoids all the time.

Steady state, only terminal A sees voltage for the vent valve solenoid.
Vehilcle Losing speed, Both terminal E and A sees voltage for the vac/vent solenoids.
Vehicle gaining speed, NO terminals see voltage to vent the servo. It's effectively as if it were "off".

1672697342335.png
 
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90hurst/oldsguy

Greasemonkey
Jan 31, 2013
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Sounds like the variable sensor throttle position coil wiring is broken (SPS). It's the feedback to the under-dash controller. With any of the coil wiring in the servo is broken or shorted, the servo and entire system will not work. Service manual says--- replace servo.

For the record, both solenoids operate independently to apply vacuum and vent the servo as needed. The servo is normally vented, and vacuum valve solenoid is normally closed. When energized, the vacuum valve opens to vacuum source but the vent valve energizes to close. These are the only places you should see voltage is when the system wants to operate. Since the car has to be above a certain mph to engage (around 25-30 mph), you should never see voltage to the servo at idle parked outside the garage. This is why they don't have you check the voltage at the servo because it would be extremely difficult to setup the car for those conditions. The controller box under the dash sends the signal output to the solenoids as needed based on the input variables and feedback from the servo position sensor (SPS) circuit. If the coils are good on resistance, it is generally expected the servo will work correctly.

Now, if you WERE able to hook up a voltmeter to your vacuum/vent solenoids circuit while driving, you should intermittently see voltage at terminals E (tan wire) for the vacuum solenoid and A (blue/white stripe wire) for the vent solenoid from the cruise module under the dash. There won't necessarily be power being sent to the solenoids all the time.

Steady state, only terminal A sees voltage for the vent valve solenoid.
Vehilcle Losing speed, Both terminal E and A sees voltage for the vac/vent solenoids.
Vehicle gaining speed, NO terminals see voltage to vent the servo. It's effectively as if it were "off".

View attachment 213758
69hurstolds this is very helpful and I have come to the conclusion after testing voltage and etc . The servo is defective and needs to be replaced and I should be good to go afterwards
 

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
8,099
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Cross your fingers. It's usually just one thing in the system that croaks and ruins your cruise control. If you've checked your cruise wand and it's good, then chances are you're golden with a servo change. Make sure you get the 4" bail. They come in different sizes.

You'll need GM p/n 25074629 or equivalent "refurbished" aftermarket. I think someone's still refurbishing these.

Ah, here we go. You'll need about 100 bucks to get one, thereabouts. Good thing you weren't getting them over the counter from the dealer, you'd pay likely twice that.

A1Cardone sells them refurbished under p/n 38-1629.

Blue Streak Electronics sells them refurbished under p/n CS2505.

Good luck.
 

90hurst/oldsguy

Greasemonkey
Jan 31, 2013
144
6
18
Cross your fingers. It's usually just one thing in the system that croaks and ruins your cruise control. If you've checked your cruise wand and it's good, then chances are you're golden with a servo change. Make sure you get the 4" bail. They come in different sizes.

You'll need GM p/n 25074629 or equivalent "refurbished" aftermarket. I think someone's still refurbishing these.

Ah, here we go. You'll need about 100 bucks to get one, thereabouts. Good thing you weren't getting them over the counter from the dealer, you'd pay likely twice that.

A1Cardone sells them refurbished under p/n 38-1629.

Blue Streak Electronics sells them refurbished under p/n CS2505.

Good luck.
Ive just replaced the cc switch/ turn signal lever because mine has been broken for the past 13yrs
 

90hurst/oldsguy

Greasemonkey
Jan 31, 2013
144
6
18
Sounds like the variable sensor throttle position coil wiring is broken (SPS). It's the feedback to the under-dash controller. With any of the coil wiring in the servo is broken or shorted, the servo and entire system will not work. Service manual says--- replace servo.

For the record, both solenoids operate independently to apply vacuum and vent the servo as needed. The servo is normally vented, and vacuum valve solenoid is normally closed. When energized, the vacuum valve opens to vacuum source but the vent valve energizes to close. These are the only places you should see voltage is when the system wants to operate. Since the car has to be above a certain mph to engage (around 25-30 mph), you should never see voltage to the servo at idle parked outside the garage. This is why they don't have you check the voltage at the servo because it would be extremely difficult to setup the car for those conditions. The controller box under the dash sends the signal output to the solenoids as needed based on the input variables and feedback from the servo position sensor (SPS) circuit. If the coils are good on resistance, it is generally expected the servo will work correctly.

Now, if you WERE able to hook up a voltmeter to your vacuum/vent solenoids circuit while driving, you should intermittently see voltage at terminals E (tan wire) for the vacuum solenoid and A (blue/white stripe wire) for the vent solenoid from the cruise module under the dash. There won't necessarily be power being sent to the solenoids all the time.

Steady state, only terminal A sees voltage for the vent valve solenoid.
Vehilcle Losing speed, Both terminal E and A sees voltage for the vac/vent solenoids.
Vehicle gaining speed, NO terminals see voltage to vent the servo. It's effectively as if it were "off".

View attachment 213758
Is there a wire that needs to be grounded since my car isn't on the ecm
 

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
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Is there a wire that needs to be grounded since my car isn't on the ecm
Not to my knowledge. At least not on a Cutlass. I've heard this ground wire may be different on Monte Carlo and people suggest cutting the VSS harness and grounding the buffer, but shouldn't be any need on your car. The ground from the VSS buffer runs to the park/neutral ECM input switch on top of the steering column, and from there it grounds to G205. The ECM is a tie in at the park/neutral switch, so if it doesn't input to something that's not there (ECM) then who cares? The speed sensor buffer feeds a separate speed input signal to the ECM, but that's about it I believe. I'm not an electrical wizard by any stretch, but the cruise setup pretty much can run on its own without the ECM the way I understand the schematics. According to the ESM, The ECM controls NOTHING on the cruise control system on your 84 Hurst/Olds. It just gets an input from the VSS buffer (which tells the ECM the car is moving so it can determine to throw a code or not in some instances).
 
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