Faulty vehicle speed sensor (VSS) or damaged wiring to the VSS, causing the PCM to misjudge actual road speed; Sticking or misadjusted cruise control servo or throttle actuator cable, holding the throttle open longer than commanded; Engine RPM signal interference or a failing crankshaft position sensor (CKP) sending erratic RPM data to the PCM; Vacuum leak or faulty cruise control vacuum servo allowing unintended throttle application; Worn or contaminated throttle body causing idle speed to hang above the cruise control enable threshold; PCM software calibration issue or internal driver fault in the cruise control circuit; Aftermarket electronic throttle controller or improperly installed remote starter interfering with cruise control signals

DTC codes / Chrysler codes / P1566

P1566 · ChryslerCruise Control System Engine RPM Too High

Q: What does code P1566 mean?

Cruise Control System Engine RPM Too High. P1566 on Chrysler vehicles means the powertrain control module (PCM) has detected that engine speed exceeded the threshold allowed while the cruise control system was active or attempting to engage. The PCM monitors engine RPM (revolutions per minute) against a calibrated maximum for cruise operation and sets this code when the signal indicates the engine is revving too high for the speed control logic to safely maintain.

P1566 on Chrysler vehicles means the powertrain control module (PCM) has detected that engine speed exceeded the threshold allowed while the cruise control system was active or attempting to engage. The PCM monitors engine RPM (revolutions per minute) against a calibrated maximum for cruise operation and sets this code when the signal indicates the engine is revving too high for the speed control logic to safely maintain.

SystemPowertrain

Code typeChrysler specific

SeverityMedium

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

Cruise control will not engage or drops out shortly after being set
The cruise control indicator lamp may flash or stay off when the button is pressed
Engine may idle or rev higher than normal, especially when the cruise system is commanded on
Transmission may shift erratically or hold gears longer than usual if the fault is speed-signal related
Often no symptoms besides the warning light, with cruise control simply becoming inoperative
Vehicle may feel like it is surging or hunting for speed when cruise is active

Common causes, most likely first

Faulty vehicle speed sensor (VSS) or damaged wiring to the VSS, causing the PCM to misjudge actual road speed
Sticking or misadjusted cruise control servo or throttle actuator cable, holding the throttle open longer than commanded
Engine RPM signal interference or a failing crankshaft position sensor (CKP) sending erratic RPM data to the PCM
Vacuum leak or faulty cruise control vacuum servo allowing unintended throttle application
Worn or contaminated throttle body causing idle speed to hang above the cruise control enable threshold
PCM software calibration issue or internal driver fault in the cruise control circuit
Aftermarket electronic throttle controller or improperly installed remote starter interfering with cruise control signals

How to diagnose and fix it

Connect a scan tool and record freeze-frame data for P1566, noting engine RPM, vehicle speed, and throttle position at the moment the code set
Inspect the cruise control servo, cable, and linkage for binding, corrosion, or incorrect adjustment, and verify the cable returns freely
Test the vehicle speed sensor signal with a scan tool while driving and compare it to a GPS or known-good reference to rule out a skewed speed reading
Check the throttle body for carbon buildup and clean it if the engine idle speed is above specification, then perform a throttle relearn if required
Inspect all vacuum hoses and the cruise servo diaphragm for leaks using a vacuum gauge or smoke machine
Verify the crankshaft position sensor signal is clean and free of dropout using an oscilloscope or live data graphing on the scan tool
If all inputs are correct, reflash or replace the PCM only after confirming the cruise control switch inputs and wiring are intact

Why RPM codes often trace to speed sensors

A skewed vehicle speed sensor can make the PCM believe the car is moving slower than it really is, so it commands a higher RPM for the requested cruise speed and trips P1566 without any obvious drivability complaint.
Aftermarket throttle controllers and pedal boosters frequently cause this code on Chrysler vehicles because they alter the electronic throttle signal in ways the cruise control logic does not expect.
A dirty throttle body that causes a slightly high idle can push engine RPM above the cruise control enable threshold, setting P1566 even though the cruise system itself is mechanically sound.
Technicians sometimes replace the cruise servo when the real problem is a chafed wire in the harness near the throttle body, so always wiggle-test the harness while watching live RPM data.
P1566 can be stored as a pending code after a single event, so clearing it and test-driving under the same conditions before replacing parts often saves unnecessary expense.

Can I keep driving with P1566?

You can usually drive the vehicle normally because the fault primarily disables cruise control, but avoid using cruise control until the repair is completed. If the engine idle is abnormally high or the vehicle surges unexpectedly, have it checked promptly because a sticking throttle actuator can become a safety concern.

Tools that help

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