Faulty speed control command switch (worn or contaminated contacts, internal short); Short to ground or chafed wiring in the switch signal circuit, often in the steering column or clockspring area; Faulty or worn clockspring (spiral cable) on models where the switch signal passes through it; Corroded or loose connector at the switch, steering column or powertrain control module; Moisture or spilled drink inside the switch or column; Faulty powertrain control module or its reference voltage supply.

P1566

Speed Control Command Switch Out of Range Low.

Mercury
Powertrain
Manufacturer code
Low severity

How this code is built

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

What it means

On a Mercury, P1566 means the powertrain control module saw the speed control (cruise control) command switch signal sitting below its expected voltage range. The switch is normally a resistor ladder on a single circuit, so a very low voltage suggests a short to ground, a faulty switch or a wiring fault. The module usually disables cruise control while the fault is present.

Symptoms

Cruise control will not engage or set
Cruise control cuts out unexpectedly
Cruise control buttons on the wheel or stalk do not respond
Cruise or speed control light flashing or not working
Check engine light on

Possible causes

Faulty speed control command switch (worn or contaminated contacts, internal short)likely
Short to ground or chafed wiring in the switch signal circuit, often in the steering column or clockspring arealikely
Faulty or worn clockspring (spiral cable) on models where the switch signal passes through itpossible
Corroded or loose connector at the switch, steering column or powertrain control modulepossible
Moisture or spilled drink inside the switch or columnpossible
Faulty powertrain control module or its reference voltage supplyrare

How to diagnose

Read the stored codes and freeze frame data, and note whether the fault is current or intermittent
Check cruise control operation and the live switch data if available, pressing each button and watching the reading change
Inspect the switch, steering column wiring and connectors for damage, moisture, corrosion or chafing
Check the cruise control fuse and any related circuit protection
Wiggle the wiring and turn the steering wheel through its full travel while watching the live switch reading for dropouts
Measure the reference voltage and signal voltage at the switch connector and compare with the wiring diagram for your model
Test the signal circuit for short to ground and check switch resistance in each button position against the specification for that vehicle
Check the clockspring and powertrain control module connector pins if the wiring and switch test good

How to fix

Replace the speed control command switch if its resistance values are out of specification
Repair or replace any shorted, chafed or damaged wiring in the signal circuit
Replace the clockspring if it is found to be faulty (procedure depends on model and airbag precautions)
Clean or repair corroded connectors and secure loose terminals
Dry out and fix the source of any water or liquid ingress, then replace contaminated components
Replace the powertrain control module only after all other causes are ruled out and the fault is confirmed

Can I keep driving?

Low severity

The car can normally be driven as usual, as the fault mainly affects cruise control. Book it in soon, and take care with any work near the steering column because of the airbag.

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