🚨 Diagnostic Profile
Vehicle Make: BUICK
Fault Description: Cruise Servo Stroke Greater Than Commanded In Cruise
This fault indicates that the Cruise Control Module has commanded a specific throttle position (stroke) via the servo unit, but the position sensor feedback is reporting an actual stroke distance that exceeds the commanded value. This typically points to a mechanical binding issue, a stretched or damaged throttle cable, or a miscalibrated/failing position sensor within the servo assembly itself.
🚨 Repair Difficulty Tier
Rating: [Intermediate]
This repair requires an intermediate skill level. While it does not involve high-liability restraint systems, it does require the use of a scan tool capable of reading bi-directional cruise control data streams, along with manual mechanical adjustment of cable linkages. A standard multimeter is also required to check resistance values on the internal position sensor (potentiometer) of the servo unit.
🛠️ Resolution Steps
Step 1: Preliminary Inspection
- Visually inspect the cruise control servo unit located in the engine bay (usually near the throttle body or fender well).
- Check the throttle cable connecting the servo to the throttle body for any fraying, stretching, or binding.
- Inspect the vacuum lines (if equipped with a vacuum-assisted servo) for cracks or disconnections.
- Check the electrical connector at the servo for corrosion or bent pins.
Step 2: Diagnostic Verification
- Connect a scan tool and access the Cruise Control Module live data stream.
- Compare the ‘Commanded Stroke’ PID against the ‘Actual Stroke’ PID while manually engaging the servo (if bi-directional controls are supported).
- Using a multimeter, backprobe the servo’s position sensor (potentiometer) wires to check for smooth, linear voltage transition as the servo arm is moved manually.
- Look for voltage spikes or dead spots in the sensor’s sweep, which indicate an internal sensor fault.
Step 3: Resolution & Reset Process
- If the cable is stretched, adjust the throttle cable tension at the bracket to eliminate slack between the servo and throttle body.
- If the internal position sensor is faulty (confirmed by inconsistent voltage reading), replace the servo unit entirely as it is typically a sealed assembly.
- Clear the Diagnostic Trouble Codes (DTCs) using the scan tool.
- Perform a road test engaging cruise control at various speeds (35mph, 55mph, 70mph) to verify the servo holds the commanded stroke without fluctuation or fault re-trigger.
📦 Parts, Labor, and Budget Estimates
Required Components/Software: Cruise Control Servo Unit, Throttle Cable (if damaged), OBD-I/OBD-II Scan Tool with GM bi-directional capabilities, Digital Multimeter.
Average Component Price: $120 – $280 (for OEM or Quality Aftermarket Servo Unit); $15 – $40 (Throttle Cable).
Estimated Labor Hours: 1.0 – 1.5 hours (Standard book time for diagnosis, cable adjustment, and/or servo replacement).