Code
P1587
HUMMER
P — Powertrain
Cruise Control Clutch Control Circuit Low
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in the cruise clutch/actuator control circuit
- Faulty cruise clutch actuator or solenoid (high resistance / open coil)
- Poor or corroded connector or ground at actuator or module
- Blown fuse or faulty relay supplying the circuit
- Faulty PCM/BCM output driver or internal module fault
- Intermittent wiring or connector fault (chafing, water intrusion)
Symptoms
- Cruise control does not engage or disengages immediately
- Cruise indicator may flash or show an error on the dash
- No audible click or movement from actuator when cruise is commanded
- Possible diagnostic trouble light (CEL) illuminated
- Intermittent cruise function or loss of speed hold
What to check
- Retrieve freeze frame and live data with a scan tool; verify P1587 and any related codes
- Visually inspect connectors, wiring harness, and actuator for damage or corrosion
- Check fuses and relays for the cruise/clutch circuit
- Back-probe actuator connector and measure control voltage while requesting cruise ON/OFF
- Measure resistance of actuator coil at connector (compare to spec if available)
- Perform wiggle test on wiring while monitoring signal for intermittent faults
Signal parameters
- Expected supply voltage: battery voltage at power feed (approx. 11–14 V)
- Control signal: typically low (~0 V) when off and driven (or a switched/pulsed voltage near battery when commanded)
- Actuator coil resistance: finite low-ohm value (check service spec) — open = very high/OL
- No-load current: measurable when actuator commanded (spec varies by design)
- Short to ground will show near 0 V on control circuit with no switch command
Diagnostic algorithm
- Connect a scan tool, confirm P1587 and note freeze frame and related codes (store before clearing).
- Inspect actuator connector and wiring visually for corrosion, damage, pin push-out, or water intrusion.
- Check related fuses and relays; replace if faulty and retest.
- Back-probe the actuator connector with key ON and while commanding cruise engage. Verify supply and control voltages change as expected.
- Measure coil resistance of the actuator. If open or out of specification, replace actuator.
- If control wire reads low (near ground) with no command, isolate wiring for short to ground using wiring diagrams. Repair short/open as needed.
- If wiring and actuator test good but the PCM/BCM output never switches correctly, check module grounds and connectors. If module output is confirmed faulty, consider module replacement only after wiring and actuator are verified.
- After repairs, clear codes and perform road test to confirm cruise engagement and ensure code does not return.
Likely causes
- Disconnected or corroded connector at cruise clutch actuator
- Broken wire between PCM/BCM and actuator (open or short to ground)
- Failed clutch actuator coil (open circuit or internal short)
- Faulty fuse or relay supplying the actuator
- Damaged ground strap or poor chassis ground at actuator mounting point
Fault status
Status
Cruise Control Clutch Control Circuit Low — control circuit is reading a low/grounded voltage preventing clutch/actuator engagement; inspect wiring, connector, fuse/relay, and actuator.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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