Cruise control quit, need some help diagnosing it?
Captain
Joined: Apr 2016
Posts: 647
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From: Alabama
Cruise Control Switches Operation
This is from the 1996 Ram Service Manual:
VEHICLE SPEED CONTROL
The Powertrain Control Module (PCM) operates the vehicle speed control system. The vehicle speed control switches are located in the steering wheel,
below the airbag. Circuit V32 from cavity C l l of the PCM supplies voltage to the Light Emitting Diode (LED) used for the speed control indicator lamp and to the speed control switches. Circuit V32 also connects to circuit
V30 through the stop lamp switch. Circuit V30 powers
the vehicle speed control servo. Circuit V37 from PCM cavity C32 connects to the vehicle speed control switches. The switches are wired in parallel and each contains a separate resistor. The voltage level present on circuit V37 (at PCM
cavity C32) depends on which speed control switch is
selected. Circuit K4 from PCM cavity A4 supplies
ground for the speed control switches.
• When the ON/OFF switch is open, the voltage level on circuit V37 at PCM cavity C32 has a nominal value of 5.0 volts with a range from 4.8 to 5.0 volts.
• When the ON/OFF switch closes, the voltage level on circuit V37 at PCM cavity C32 has nominal
value of 1.51 volts with a range from 1.31 to 1.61
volts.
• When the SET/COAST switch closes, the voltage level on circuit V37 at PCM cavity C32 has nominal value of 3.8 volts with a range from 3.6 to 3.9 volts.
• When the RESUME/ACCEL switch closes, the voltage level on circuit V37 at PCM cavity C32 has nominal value of 4.4 volts with a range from 4.2 to
4.5 volts.
If there is no, or zero, volts here, the LED will not light, and the cruise control will not work, as I said earlier.
When the brake pedal is depressed, the stop lamp switch opens and disconnects circuits V40 and Z l, and circuits V32 and V30. When the stop lamp switch disconnects circuits V32 and V30, power is removed from the speed control servo.
If the brake (stop lamp) switch is defective, or stuck on, the cruise control will never work. This is why I suggested verifying its operation in the beginning.
VEHICLE SPEED CONTROL
The Powertrain Control Module (PCM) operates the vehicle speed control system. The vehicle speed control switches are located in the steering wheel,
below the airbag. Circuit V32 from cavity C l l of the PCM supplies voltage to the Light Emitting Diode (LED) used for the speed control indicator lamp and to the speed control switches. Circuit V32 also connects to circuit
V30 through the stop lamp switch. Circuit V30 powers
the vehicle speed control servo. Circuit V37 from PCM cavity C32 connects to the vehicle speed control switches. The switches are wired in parallel and each contains a separate resistor. The voltage level present on circuit V37 (at PCM
cavity C32) depends on which speed control switch is
selected. Circuit K4 from PCM cavity A4 supplies
ground for the speed control switches.
• When the ON/OFF switch is open, the voltage level on circuit V37 at PCM cavity C32 has a nominal value of 5.0 volts with a range from 4.8 to 5.0 volts.
• When the ON/OFF switch closes, the voltage level on circuit V37 at PCM cavity C32 has nominal
value of 1.51 volts with a range from 1.31 to 1.61
volts.
• When the SET/COAST switch closes, the voltage level on circuit V37 at PCM cavity C32 has nominal value of 3.8 volts with a range from 3.6 to 3.9 volts.
• When the RESUME/ACCEL switch closes, the voltage level on circuit V37 at PCM cavity C32 has nominal value of 4.4 volts with a range from 4.2 to
4.5 volts.
If there is no, or zero, volts here, the LED will not light, and the cruise control will not work, as I said earlier.
When the brake pedal is depressed, the stop lamp switch opens and disconnects circuits V40 and Z l, and circuits V32 and V30. When the stop lamp switch disconnects circuits V32 and V30, power is removed from the speed control servo.
If the brake (stop lamp) switch is defective, or stuck on, the cruise control will never work. This is why I suggested verifying its operation in the beginning.
Last edited by Friar Tuck; Jul 11, 2016 at 07:31 PM. Reason: Highlight and add stop light switch info
Captain
Joined: Apr 2016
Posts: 647
Likes: 3
From: Alabama
Friar Tuck,
Yes, pin 1 (YL/RD) on C11 has 0 volts. C32 (RD/LG) has 5 volts. It will be a couple of weeks till payday and then I can get a clock spring. The wire that connects to C32 is broken and I don't get power to the switch right now.
Friar Tuck,
Are you referring to the pins on the switch? Or pins on the back of the clock spring. Wiring on the back of the clock spring is #1 YL/RD, #3 BK/LB and #4 RD/LG just like it's listed in the service manual. The BL/LB is the ground, the other two: #1 YL/RD is the ground and #4 RD/LG is 5 volts.
I'll let everyone know how this turns out and give an update when I get a new clock spring.
Yes, pin 1 (YL/RD) on C11 has 0 volts. C32 (RD/LG) has 5 volts. It will be a couple of weeks till payday and then I can get a clock spring. The wire that connects to C32 is broken and I don't get power to the switch right now.
Friar Tuck,
Are you referring to the pins on the switch? Or pins on the back of the clock spring. Wiring on the back of the clock spring is #1 YL/RD, #3 BK/LB and #4 RD/LG just like it's listed in the service manual. The BL/LB is the ground, the other two: #1 YL/RD is the ground and #4 RD/LG is 5 volts.
I'll let everyone know how this turns out and give an update when I get a new clock spring.
This should be at 5 volts, not ground.
The voltage at #4 will vary, depending on which switch is depressed.
Thread Starter
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Registered User
Joined: Jul 2016
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From: Southeastern WA
On mine the #4 RD/LG is 5 volts, which goes to the PCM C32. My PCM C11 has no voltage coming from it
Captain
Joined: Apr 2016
Posts: 647
Likes: 3
From: Alabama
The references to circuit V37 are for #4 RD/LG. With no switch pressed, you will see ~5 volts. As you press a switch as explained in the previous post, the voltage will be different.
C11 at the PCM should provide 5 volts. Please find the brake switch and unplug it to see if the 5 volts is at C11.
C11 at the PCM should provide 5 volts. Please find the brake switch and unplug it to see if the 5 volts is at C11.
Thread Starter
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Registered User
Joined: Jul 2016
Posts: 16
Likes: 0
From: Southeastern WA
Unplugged the brake switch as stated in an earlier post and it made no difference as too the cruise working. Would there be 5 volts at V37, if the connector was disconnected from the PCM? That would also disconnect V32.
I also stated in an earlier post that my clock spring is bad and I will be replacing it.
I also stated in an earlier post that my clock spring is bad and I will be replacing it.
Captain
Joined: Apr 2016
Posts: 647
Likes: 3
From: Alabama
The brake switch, IIRC, has three circuits through it. 2 are normally closed (open when pedal is depressed) and one is normally open. Just unplugging probably won't do it.
DBBD1 is correct. I misread the diagram for the brake switch and the speed control servo connection. I thought the brake switch applied ground from the control servo to disable the input (V32) from the PCM. I apologize for the trouble.
Unplugged the brake switch as stated in an earlier post and it made no difference as too the cruise working. Would there be 5 volts at V37, if the connector was disconnected from the PCM? That would also disconnect V32. I also stated in an earlier post that my clock spring is bad and I will be replacing it.
The cruise will not work until you replace the broken clockspring.
No, there will not be 5 volts at V37 if the connector was disconnected from the PCM.
You are correct, that would also disconnect V32.
Even with the broken clockspring, connect the PCM, and there should be 5 volts on both the V32 and V37 circuits.
So do we have 5 volts on the V32 circuit at the clockspring?
I was trying to determine whether 5 volts was coming from the PCM to pin 1(V32) on the YELLOW/RED wire with everything plugged in.
Once you replace the clockspring, and plug everything in, the LED should light and the cruise control should work.
We can then see if the switches work as they should.
DBBD1 is correct. I misread the diagram for the brake switch and the speed control servo connection. I thought the brake switch applied ground from the control servo to disable the input (V32) from the PCM. I apologize for the trouble.
Unplugged the brake switch as stated in an earlier post and it made no difference as too the cruise working. Would there be 5 volts at V37, if the connector was disconnected from the PCM? That would also disconnect V32. I also stated in an earlier post that my clock spring is bad and I will be replacing it.
The cruise will not work until you replace the broken clockspring.
No, there will not be 5 volts at V37 if the connector was disconnected from the PCM.
You are correct, that would also disconnect V32.
Even with the broken clockspring, connect the PCM, and there should be 5 volts on both the V32 and V37 circuits.
So do we have 5 volts on the V32 circuit at the clockspring?
I was trying to determine whether 5 volts was coming from the PCM to pin 1(V32) on the YELLOW/RED wire with everything plugged in.
Once you replace the clockspring, and plug everything in, the LED should light and the cruise control should work.
We can then see if the switches work as they should.