01 Turbocharged Engine Maintenance: Dos and Don’ts • 02 How to Diagnose and Fix Issues with Your Start Engine Push … • 03 What Causes a Car Engine to Use More Water? • 04 New Engines Use Tiny Explosions Of Air Instead Of Spark Plu… • 05 C0050 - Right Rear Wheel Speed Circuit Malfunction • 06 Battery Troubleshooting: When to Replace or Recharge • 07 What Is Blow-By & How to Prevent It From Harming Your Engine • 08 How Adaptive Cruise Control Actually Works • 09 P0050, P0051, and P0052: H02S heater control circuit (Bank … • 10 Engine Cranking Noises: Guide to Identifying and Tackling C… •

DTC codes / GM codes / P1550

P1550 · GMCruise Control Motor Actuator Circuit

P1550 on a GM vehicle means the powertrain control module (PCM) has detected an electrical fault in the cruise control motor actuator circuit, which is the servo motor that physically moves the throttle cable or linkage to hold a set speed. The PCM monitors the actuator's command and feedback circuits and sets this code when the current or voltage on the motor circuit falls outside the expected range during a cruise control command or self-test.

SystemPowertrain
Code typeGM specific
SeverityLow
Fix difficultyIntermediate
AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

  • The cruise control will not engage at all when you press the set button, or it drops out as soon as you release the accelerator.
  • The cruise control indicator light on the dash may flash or stay off entirely when you try to activate the system.
  • The engine may idle erratically or the throttle may feel sticky if the actuator is binding and holding the cable slightly open.
  • Often no symptoms besides the warning light, because the PCM disables cruise control but leaves normal throttle operation untouched.
  • A slight surge or hesitation during steady-speed driving if the actuator motor is drawing excessive current and the PCM is limiting its duty cycle.
  • On some GM trucks and SUVs, the cruise control may work intermittently before failing completely as the motor brushes wear.

Common causes, most likely first

  1. A failed cruise control motor actuator servo, typically worn brushes or a seized internal gearset inside the actuator housing.
  2. Corroded, chafed, or broken wires in the actuator harness, especially where the cable runs near the throttle body or through the firewall grommet.
  3. A poor ground connection at the actuator mounting bolt or the chassis ground point shared with the cruise control module.
  4. A faulty cruise control switch or stalk that sends an implausible command to the PCM, causing the PCM to flag the actuator circuit indirectly.
  5. A binding or misadjusted cruise control cable that forces the actuator motor to draw too much current, tripping the circuit fault.
  6. A failing PCM driver circuit on older GM vehicles where the cruise control output is integrated into the PCM rather than a separate module.
  7. Water intrusion into the actuator connector or the underhood fuse box that feeds the cruise control circuit.

How to diagnose and fix it

  1. Inspect the cruise control actuator connector and the full length of its harness for corrosion, chafing, or loose pins, and clean or repair as needed.
  2. Check the actuator ground circuit with a multimeter set to resistance, confirming less than one ohm from the actuator housing to the battery negative post.
  3. Command the cruise control actuator with a scan tool that supports GM bidirectional controls and watch for smooth motor movement and correct feedback voltage.
  4. Measure the actuator motor resistance across its terminals and compare to the GM service specification for your engine and model year.
  5. Inspect the cruise control cable for binding, kinks, or incorrect adjustment at the throttle body, and lubricate or replace the cable if it does not move freely.
  6. Test the cruise control switch inputs at the PCM connector with a scan tool to confirm the PCM is receiving valid set, resume, and cancel commands.
  7. Replace the cruise control motor actuator if the motor draws excessive current or fails to respond to a bidirectional command, then clear the code and verify cruise engagement on a road test.

What a GM cruise actuator code really means

  • A binding cruise control cable is the most commonly missed cause of P1550 on older GM trucks, because the actuator motor tests fine on the bench but overloads in the vehicle when it has to pull against a sticky cable.
  • The PCM sets P1550 based on current and feedback plausibility, so a perfectly good actuator can trigger the code if the ground reference is corroded or the connector pins are backed out of the housing.
  • On many GM vehicles the cruise control actuator shares a fuse and ground with the horn or the brake switch circuit, so a blown fuse or bad brake switch can disable cruise and set this code without any actuator fault at all.
  • A scan tool that can command the actuator is essential; resistance checks alone will not reveal a motor that spins freely but fails to return, which is a common wear pattern on high-mileage GM servos.
  • Do not replace the PCM until you have load-tested the actuator circuit with a bulb or a test light, because a shorted actuator motor can mimic a failed PCM driver and lead to an expensive misdiagnosis.

Can I keep driving with P1550?

It is safe to keep driving with P1550 because the PCM disables cruise control but leaves normal throttle control intact, so the vehicle remains fully drivable. Avoid using cruise control until the fault is repaired, and address any binding cable promptly so the throttle does not stick open.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage