Faulty speed control switch, or one stuck or worn internally (often in the steering wheel or column switch assembly); Speed control switch signal wire shorted to ground, for example chafed insulation; Damaged clockspring or steering column wiring where the switch circuit passes through (depends on model); Corroded, damaged or loose connector in the switch circuit or at the powertrain control module; Moisture or contamination inside the switch housing holding the circuit low; Fault in the powertrain control module's switch input circuit.

P1597

Speed Control Switch Always Low.

Plymouth
Powertrain
Manufacturer code
Low severity

How this code is built

P: SystemPowertrain
1: Defined byThe manufacturer
5: AreaVehicle speed, idle control and auxiliary inputs
97: FaultThe specific fault in that area

What it means

On Plymouth models, P1597 means the powertrain control module has seen the speed control (cruise control) switch circuit sit at a low voltage and stay there, even when no cruise button is being pressed. The module expects the signal to change as the driver presses the switch, so a signal stuck low suggests a short to ground, a stuck switch or a wiring fault. The cruise control is normally disabled while the fault is present.

Symptoms

Cruise control will not engage or set a speed
Cruise control drops out or cancels unexpectedly
Cruise control on/off or set/resume buttons seem unresponsive
Check engine light on
Cruise control indicator light behaving oddly or not lighting

Possible causes

Faulty speed control switch, or one stuck or worn internally (often in the steering wheel or column switch assembly)likely
Speed control switch signal wire shorted to ground, for example chafed insulationlikely
Damaged clockspring or steering column wiring where the switch circuit passes through (depends on model)possible
Corroded, damaged or loose connector in the switch circuit or at the powertrain control modulepossible
Moisture or contamination inside the switch housing holding the circuit lowpossible
Fault in the powertrain control module's switch input circuitrare

How to diagnose

Read the stored codes and freeze frame data, and note whether other cruise, brake switch or speed-related codes are present.
Check the cruise control switch's live data or voltage on a scan tool with no buttons pressed, then see whether it changes as each button is pressed.
Visually inspect the steering column and wheel switch area, plus the wiring and connectors, for damage, water ingress, corrosion or pinched wires.
Press and release each cruise button and check for sticking or a poor feel, and see whether the reading follows.
Unplug the switch connector and check whether the signal rises to the reference value; if it does, the switch is suspect, and if it stays low, the wiring is suspect.
Test the signal wire for a short to ground and check circuit continuity and ground integrity against the wiring diagram for the specific model and year.
Check the clockspring circuit if fitted, following the manufacturer's safe procedure for airbag systems.
Only after the switch and wiring are proven good, check the powertrain control module's input and power supplies.

How to fix

Replace the faulty speed control switch or switch assembly.
Repair or replace shorted or chafed wiring in the switch circuit.
Clean, repair or replace corroded or damaged connectors and terminals.
Replace a faulty clockspring if testing proves it is the cause, observing airbag safety precautions.
Dry out and resolve any source of moisture ingress, then recheck the circuit.
Repair or replace the powertrain control module only if testing confirms an internal fault.

Can I keep driving?

Low severity

The car is normally fine to drive, but cruise control will probably not work. Book it in at your convenience, and avoid driving if the steering controls or airbag warning are also affected.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.