What Does P056B Mean?
The ECM has detected a malfunction in the cruise control 'Decrease Distance' signal circuit, used on vehicles equipped with adaptive cruise control (ACC). This signal commands the ACC system to reduce the following distance to the vehicle ahead. The ECM is not receiving a valid decrease distance command when the driver presses the corresponding button.
Common Causes
40%
Faulty distance decrease button in the steering wheel ACC switch module with worn contacts or stuck mechanism
25%
Open or corroded wiring in the distance decrease signal circuit between steering wheel and ACC module
25%
Clock spring failure on the distance decrease signal trace
10%
ACC control module input fault preventing recognition of the decrease distance voltage level
Diagnostic Steps
1
Step 1: With ACC active and following a vehicle, press the distance decrease button. The gap indicator should decrease by one step. Monitor the instrument cluster display for any response.
2
Step 2: Backprobe the ACC distance signal at the control module while pressing the decrease button. Verify the voltage changes to the expected level for the decrease command.
3
Step 3: Measure switch contact resistance at the decrease position and compare to manufacturer specifications. A deviation of more than 10% from the specified resistance value will cause the module to reject the input.
4
Step 4: If other ACC button functions work correctly, isolate the fault to the specific decrease contact within the switch assembly or the clock spring trace carrying that signal.
5
Step 5: Replace the steering wheel switch module if the decrease contact is faulty. If the clock spring is at fault, replace the entire assembly. Verify all ACC button functions operate correctly after repair.
Estimated Repair Cost
$50 - $400
Parts + labor, varies by vehicle and location
The ECM has detected a malfunction in the cruise control 'Decrease Distance' signal circuit, used on vehicles equipped with adaptive cruise control (ACC). This signal commands the ACC system to reduce the following distance to the vehicle ahead. The ECM is not receiving a valid decrease distance com...
The most common cause of P056B (Cruise Control "Decrease Distance" Signal) is: Faulty distance decrease button in the steering wheel ACC switch module with worn contacts or stuck mechanism
Typical repair costs for P056B range from $50 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The driver cannot decrease the ACC following distance via the button, but the current gap setting remains active and the system continues to maintain safe following distance. All other ACC and cruise functions remain operational.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P056B to identify the root cause.
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Quick Info
Category
Powertrain
System
Adaptive Cruise Control System
Difficulty
Type
Generic (SAE)
Recommended Tools
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