About a year ago my resume button stopped working for cruise control and now about 3 weeks ago the cruise control stopped working altogether. How can I troubleshoot this?

step 1
Remove the left sound insulator
step 2
the stop switch is here, way way up top
use flash light to see it.
it is there.
top of pedal it is there. SM books step1.

buy the service manual.?
if the switch ever sticks on , cruise ENDS
it is a NO, switch normally open contarts
no calibration is stated so its PnP

Do you know how it works ? What controls it ?

Did you hook up a scan tool an check for DTC'S - diagnostic trouble codes ?

Cruise Control Description and Operation
Cruise control is a speed control system that maintains a desired vehicle speed under normal driving conditions. However, steep grades may cause variations in the selected speeds. The electronic cruise control system has the capability to CRUISE, COAST, RESUME SPEED, ACCELERATE, TAP-UP or TAP-DOWN.
The main parts of the cruise control system are:
• The powertrain control module (PCM)
• The function control switches
• The stop lamp switch assembly
The cruise control system uses the powertrain control module (PCM) to maintain the desired vehicle cruise speed . The PCM assembly contains a low speed limit which will prevent system engagement below a minimum speed of 40 km/h (25 mph). The PCM assembly is not serviceable.
Cruise control operation is controlled through the function control switches located on the multifunction turn signal lever. The cruise control function control switches includes the ON/OFF, SET/COAST, R/A (resume/accelerate). The switch assembly provides driver control of the cruise control system.
The stop lamp switch is used to disengage the cruise control. A cruise control release switch circuit and a stop lamp switch circuit are used. The stop lamp switch is mounted to the brake pedal bracket . To disengage the system the driver presses the brake pedal. The speed of the vehicle at brake actuation will be stored in the memory of the PCM.
With cruise control, the vehicle can maintain a speed of about 40 km/h (25 mph) or more without keeping your foot on the accelerator. When the driver turns off the cruise control ON/OFF switch or ignition switch, the cruise control turns off. The vehicle speed stored in the memory of the PCM will be lost.
Ignition positive voltage is supplied from the HVAC fuse, to the cruise control switch. When the cruise control ON/OFF switch is on, ignition positive voltage is applied to the cruise on switch signal circuit terminal of the PCM. If the driver has not pressed the brake pedal, ignition positive voltage is supplied through the stop lamp switch, TCC/Brake signal contacts to the cruise control brake pedal switch signal circuit terminals of the PCM. Cruise control is canceled when the driver presses the brake pedal. The stop lamp switch contacts close, applying battery positive voltage to the stop lamp signal circuit of the PCM. At the same time, the TCC/Brake contacts of the stop lamp switch open and voltage is removed from the brake pedal signal circuit at the PCM. When pressing the SET/COAST button on the multifunction turn signal lever, ignition positive voltage is applied to the set/coast switch signal terminal of the PCM. When pressing the R/A (resume/accelerate) on the control switch, ignition positive voltage is applied to the resume/accelerate switch signal terminal of the PCM.
When the cruise switch is in the ON position, and the driver presses the SET/COAST button, the PCM then checks to see that the cruise control enable criteria is met. If the cruise control criteria has been met the PCM sends a class 2 message to the instrument panel cluster (IPC) to illuminate the cruise light.
The PCM will inhibit cruise control:
• When the PCM detects that the center high mounted stop lamp (CHMSL) in not operating properly.
• When vehicle speed is less than 40 km/h (25 mph).
• When in PARK, REVERSE, NEUTRAL, or 1st gear.
• With low engine RPM
• With high engine RPM (fuel cut-off)
• When vehicle speed is to high
• When an over or under charged battery voltage condition exists
• Antilock brake system/traction control system is active for more than 2 seconds
If the PCM determines that any of the cruise control inhibit conditions are present, the PCM will disengage the cruise control. If the PCM disables the cruise control for an inhibiting event it will record the reason for disengagement in the Disengage Definition data file.

Do you know how to test electrical circuits with a DVOM - digital volt ohmmeter, looking at a wiring diagram for the CC so you know what wires to test , if not your best bet might be to take it to a qualified repair shop .

Which engine does your trailblazer have 5.3 or 4.2 L
Cruise Control Description and Operation (5.3L)
Cruise Control Description and Operation (4.2L)
makes a difference ! The best way to start diagnostic's is with a scan tool . May have DTC'S diagnostic trouble codes .
DTC P1574 Stop Lamp Switch Circuit
DTC P0568 Cruise Control Set Switch Circuit
DTC P0567 Cruise Control Resume Switch Circuit
Plus with a scan tool you can see if the cruise control switch is inputing to PCM. Data list .
The cruise control resume/accel switch is an input to the powertrain control module (PCM). The PCM uses the cruise control resume/accel switch signal circuit in order to detect when the driver has requested to accelerate the set vehicle speed or to resume the cruise control system. The PCM detects a voltage signal on the cruise control resume/accel switch signal circuit when the switch is applied. This DTC sets if the PCM senses voltage on the cruise control resume/accel switch signal circuit for longer than 90 seconds.
Cruise Control Indicator Inoperative (4.2L)
Turn OFF the ignition.
Install a scan tool.
Turn ON the ignition, with the engine OFF.
With the scan tool, Command the Cruise Control Lamp Test parameter ON, in the instrument panel cluster (IPC) Output Controls.
Does the Cruise indicator illuminate in the IPC?
YES - Go to Step 3
no - Go to Step 4
3
Inspect for poor connections at the harness connector of the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?
YES - Go to Step 7
NO - Go to Step 6
4
Inspect for poor connections at the harness connector of the IPC. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?
YES - Go to Step 7
NO - Go to Step 5
5
Replace the IPC. Refer to Control Module References for replacement, setup, and programming.
Did you complete the replacement?
YES - Go to Step 7
--
6
Replace the PCM. Refer to Control Module References for replacement, setup, and programming.
Did you complete the replacement?
Go to Step 7
--
7
Operate the system in order to verify the repair.
Does the system operate properly?
System OK
Go to Step 2

Cruise Control Inoperative/Malfunctioning (4.2L)

Install a scan tool.
Turn ON the ignition, with the engine OFF.
Press the cruise ON/OFF switch OFF.
With the scan tool, observe the Cruise ON/OFF switch parameter in the powertrain control module (PCM) Cruise Control Data list.
Does the Cruise ON/OFF switch parameter display OFF?

Your best bet mite be to take your vehicle to the dealer .

Terrible news for you, you may have already figured out.
These accessories are in the category of : " Be thankful it lasted this long " !
Now, about a fix.
Here are some of the things that have caused my cruise to stop working.
Check these out on yours.
1) The engine mounts got loose, affecting the adjustment of the cruise control to the throttle body.
2) The cruise throttle body got loose on the inner fender due to loose screws or out-of-adjustment brackets.
3) The brake pedal switch got loose and caused the cruise to think you were pressing the brake when you weren't.
4) The drive shaft sensor/magnet fell off because of old age. (The glue failed)
God bless your efforts.

worn out possibly or gummed button. Or does it stop working while in cruise control? Does the resume work and accelerate button during operation?

Once you have turned your cruise control on accelerate to desired speed press SET button on right hand side of steering wheel before lifting foot from accelerator, then remove foot from accelerator. pushing RESUME button will deactivate cruise control without turning it off. Then when clear of traffic push resume again to activate cruise control. It will automatically resume to previous set speed.

1. if not already done, set the parking brake.
2. turn the ignition switch to the ON position.
3. turn cruise control on
4. turn cruise control off
5. turn cruise control on
6. very rapidly push the RESUME button four times and then hold for four seconds on the fifth time.
7. oil change light should clear.
8. the time the cruise control is turned on for the second time to the time the fifth activation of the resume button is held down must be within 6-7 seconds, if not you must repeat the process.

Hi. My wifes cruise was acting up on her Buick and lifting up firmly on the brake pedal solved the problem.

Sounds like your clock spring may be going bad. The blinking cruise control symbol is a warning that you are traveling at a high speed. That is nothing to really worry about.

Pull the instrument panel connector off at the rear of cluster and look for any damaged connections, clean it and reconnect, that may cure the issue, the cruise problem may be the rotating contact in the steering wheel, it is called the clocksprimng contact because that is what it looks like, changing this part is not for the DIY mechanic, the driver airbag must be dis-armed correctly or serious injury will occur if the bag goes off, the very least it will scare the H... out of you, if you are lucky....