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DTC codes / GM codes / P1597

P1597 · GMSpeed Control Switch Always Low

P1597 on GM vehicles means the powertrain control module (PCM) has detected that the speed control switch circuit is stuck at a low voltage, typically ground, for longer than expected. The PCM monitors the steering wheel cruise control switch inputs and interprets a continuous low signal as a switch that is always pressed or a wiring short to ground.

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

Symptoms you may notice

  • The cruise control system does not engage or cancels immediately after being set.
  • The cruise control indicator light may flash or stay off when you try to activate it.
  • Often no symptoms besides the warning light, especially if the fault is intermittent.
  • The horn, audio controls, or other steering wheel functions may also stop working if they share the same clock spring circuit.
  • The engine may run normally with no drivability complaints, as this code does not affect engine performance.

Common causes, most likely first

  1. A short to ground in the speed control switch wiring, often where the harness flexes near the steering column.
  2. A faulty clock spring (spiral cable) inside the steering wheel that has worn through and is shorting the switch signal to ground.
  3. A stuck or internally shorted speed control switch assembly on the steering wheel.
  4. Corrosion or water intrusion in the switch connector or inline harness connectors.
  5. A chafed wire rubbing against metal under the dash or near the steering column.
  6. A faulty powertrain control module (PCM) that is misreading the switch input, though this is rare.

How to diagnose and fix it

  1. Use a scan tool to read the speed control switch data and confirm the switch is stuck in the low or pressed position.
  2. Inspect the steering wheel switches and connector for sticking buttons, corrosion, or loose pins.
  3. Check the clock spring for continuity and shorts by testing the switch signal circuit through the steering column while turning the wheel.
  4. Disconnect the PCM and measure resistance from the switch signal wire to ground to check for a short in the harness.
  5. Repair any chafed or shorted wires, replace the clock spring if faulty, or replace the switch assembly as needed.
  6. Clear the code and test the cruise control operation through all switch functions to verify the repair.

Don't overlook the clock spring

  • A shorted clock spring is one of the most common causes of P1597 on GM vehicles, yet many technicians replace the steering wheel switches first and the code returns.
  • The speed control switch circuit often shares a ground or signal path with the horn and audio controls, so a single short can disable multiple steering wheel functions.
  • P1597 can set intermittently if the wiring only shorts when the steering wheel is turned to a specific position, making it hard to reproduce in the shop.
  • A stuck cruise control switch can sometimes be freed by rapidly pressing all buttons, but if the code resets immediately, the fault is in the wiring or clock spring.
  • Do not replace the PCM for P1597 unless every other circuit has been ruled out, because the PCM is rarely the cause of a low switch signal.

Can I keep driving with P1597?

You can drive the vehicle normally because P1597 only affects the cruise control system and does not impact engine operation or safety. Avoid using cruise control until the fault is repaired, as it may not engage or could disengage unexpectedly.

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.

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