A faulty brake pedal position switch or clutch pedal switch that keeps the inhibit circuit grounded or open.; Damaged, chafed, or corroded wiring in the cruise inhibit circuit, especially near the pedals or under the hood.; A poor ground connection at the PCM or at the switch mounting point.; A failed cruise control module or switch assembly on the steering wheel.; A PCM software glitch or internal driver fault that misreads the inhibit circuit.; Aftermarket accessories tapped into the brake or cruise wiring, such as alarm or remote-start systems.

DTC codes / GM codes / P1585

P1585 · GMCruise Inhibit Control Circuit

Q: What does code P1585 mean?

Cruise Inhibit Control Circuit. P1585 on GM vehicles means the powertrain control module (PCM) has detected a fault in the cruise inhibit control circuit, which is the wiring that lets the PCM disable cruise control when conditions are unsafe. The PCM monitors the circuit for unexpected voltage or continuity and sets this code when the signal does not match what the software expects.

P1585 on GM vehicles means the powertrain control module (PCM) has detected a fault in the cruise inhibit control circuit, which is the wiring that lets the PCM disable cruise control when conditions are unsafe. The PCM monitors the circuit for unexpected voltage or continuity and sets this code when the signal does not match what the software expects.

SystemPowertrain

Code typeGM specific

SeverityLow

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

Cruise control will not engage at all when you press the set button.
Cruise control engages briefly and then drops out on its own.
The cruise indicator light on the dash may flash or stay off entirely.
Often no symptoms besides the warning light, with the vehicle driving normally.
Other driver-assist features that share the cruise inhibit signal may stop working.

Common causes, most likely first

A faulty brake pedal position switch or clutch pedal switch that keeps the inhibit circuit grounded or open.
Damaged, chafed, or corroded wiring in the cruise inhibit circuit, especially near the pedals or under the hood.
A poor ground connection at the PCM or at the switch mounting point.
A failed cruise control module or switch assembly on the steering wheel.
A PCM software glitch or internal driver fault that misreads the inhibit circuit.
Aftermarket accessories tapped into the brake or cruise wiring, such as alarm or remote-start systems.

How to diagnose and fix it

Connect a scan tool and record all stored and pending codes, then clear P1585 and test-drive to see if it returns immediately.
Inspect the brake pedal switch and clutch pedal switch for proper adjustment, continuity, and corrosion, and replace if faulty.
Visually inspect the cruise inhibit circuit wiring for chafing, pinched insulation, or loose connectors, especially around the pedal assembly and steering column.
Check ground connections at the PCM and at the switch mounting points for tightness and clean metal contact.
Use a multimeter to measure voltage and resistance on the inhibit circuit at the PCM connector while operating the brake and clutch pedals, comparing to the service manual specification.
If the circuit and switches test good, reflash or replace the PCM only after confirming all other possibilities are ruled out.

Before you replace the cruise control module

A misadjusted brake pedal switch is the most common cause of P1585 on GM trucks and SUVs, and it often sets no other brake-related codes.
The cruise inhibit circuit is separate from the brake light circuit on many GM models, so the brake lights can work perfectly while the inhibit signal is faulty.
Aftermarket remote starters and alarm systems frequently tap into the brake or clutch switch wiring and create intermittent inhibit faults that only appear in certain temperatures.
A weak battery or poor ground can cause the PCM to misread the inhibit circuit without any hard wiring fault, so load-test the battery before condemning parts.
P1585 does not always mean the cruise control is broken; some GM vehicles set it when the inhibit circuit is open but cruise still functions, leading owners to ignore a real safety issue.

Can I keep driving with P1585?

The vehicle remains safe to drive because the fault only affects cruise control, but avoid using cruise until the repair is complete since the system may not disengage as designed. Have the circuit inspected soon, especially if the brake or clutch switch is suspected.

Tools that help

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Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.