Code
P1563
BUICK
P — Powertrain
Cruise Vehicle Speed/Set Speed Difference Too High
AI status
Completed
Completed
100%
Causes
- Faulty or intermittent Vehicle Speed Sensor (VSS) or ABS wheel speed sensor(s)
- Damaged or corroded wiring or connectors on speed sensor circuits or CAN bus
- Mismatched or incorrect tire/wheel size or incorrect tire pressure causing speed reading error
- Faulty cruise control module, PCM/ECM, or ABS module providing incorrect speed data
- Faulty brake or clutch interlock switch (system sees a brake/clutch input)
- Software calibration/firmware issue or lost module learned values
Symptoms
- Cruise control will not engage, set, or resume
- Cruise disengages immediately after setting or while active
- Inconsistent speedometer or intermittent speed readout on scan tool
- Cruise system or malfunction indicator on dash
- Transmission shift anomalies or unexpected downshifts (if speed data incorrect)
What to check
- Read all stored codes and freeze frame data with a capable scan tool; note related ABS/BCM/TCM/PCM codes
- Compare vehicle speed reported by PCM, ABS module and instrument cluster using a scan tool while driving
- Visually inspect VSS and wheel speed sensor wiring, connectors, and grounds for damage or corrosion
- Check tire size/pressure and confirm they match vehicle configuration and calibration
- Verify brake pedal and clutch interlock switches operate correctly (no false inputs)
- Inspect for recent module replacements or aftermarket devices that alter speed signals
Signal parameters
- Vehicle speed (VSS) signal should be steady and match instrument cluster speed within a few km/h
- Wheel speed sensors should show consistent RPMs for all wheels at steady speed
- Cruise set speed value should be within a small tolerance of the actual vehicle speed when set (typically only a few km/h/MPH)
- No frequent dropouts or spikes in the speed signal on a live-data capture
- Brake/clutch switch state must remain inactive (no brake input) when attempting to set cruise
Diagnostic algorithm
- Retrieve codes from PCM, ABS, BCM and related modules. Note freeze-frame and live data when the code set.
- Clear codes and attempt to reproduce the condition under controlled road test while recording vehicle speed, set speed and sensor signals with a scan tool.
- Compare speed readings from PCM, ABS module and instrument cluster; if one module differs, trace wiring and connectors to that module.
- Inspect and test the Vehicle Speed Sensor and wheel speed sensors; check resistance and signal waveform if possible.
- Verify brake pedal and clutch switches operate and do not show false inputs; check their connectors and adjust/replace if needed.
- Check tire size/pressure and correct if mismatched or reprogram calibration values if tires/wheels were changed.
- Repair any damaged wiring, connectors or grounds found. Replace faulty sensors or modules as indicated by testing.
- If module replacement is performed, perform required relearn/calibration or software updates. Re-scan to confirm no further codes and perform road test.
- If intermittent or communication errors persist, investigate CAN-bus wiring, terminations and module power/grounds.
Likely causes
- Vehicle speed sensor (VSS) failure or intermittent signal
- Damaged sensor wiring or poor connector/ground
- ABS wheel speed sensor out of tolerance or providing inconsistent readings
- Brake light switch or clutch switch stuck/false input disabling cruise
- Tire size changed or incorrect TPMS/calibration causing speed mismatch
Fault status
Status
PCM/cruise module detected vehicle speed vs set speed difference above allowable threshold. Cruise control disabled until speed signal discrepancy is resolved.
Repair difficulty: Medium
Diagnostic time: 1.5-3.0 hours
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