Error Code P056B is defined as P056B Cruise Control Decrease Distance Signal. This code is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made from 1996 up to the present. It’s also more common among Audi, Citroen, Chevrolet, Ford, Hyundai, Nissan, Peugeot, and Volkswagen vehicles. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model, powertrain configuration type, to another.
Cruise Control comes with multiple functions; the driver can set a specific speed for the vehicle and maintain it using numerous sensors, modules, switches, and various components, as well as modify the speed electronically (using “set –“ and “set +”), and even temporarily modify speed while storing previous speed (often used in passing vehicles, unexpected slowing or stopping), etc.
Since this code is contained within one switch/component, it is important to locate the mechanical inputs (buttons, switches, talks, etc.) involved. With that said, some common names for the said component are:
- Multi-function switch
- Cruise control switch
- Cruise control module
- Steering wheel controls
- Accessory switch
If the PCM determines a fault within one or more of cruise control functions, it will trigger the CEL (Check Engine Light) and register a specific code. The use of said function will act abnormally and become disabled.
When Error Code P056B is stored, that means the PCM has determined a malfunction in the DECREASE DISTANCE signal of the ACC (Adaptive Cruise Control).
Other related error codes include:
As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other common symptoms include:
- Defective cruise control
- Cruise control light in the dash is constant or not coming
- Cruise control cannot be set to desired speed or speed is erratic
- Shorted or open wiring
- Blown fuse which may indicate a serious problem
- Non-operative cruise control system (i.e. Accel, Coast, Resume, Set, +, -)
- Commands not working properly
- Damaged or defective cruise control switch or buttons
- No effective electrical connection in the connector(s)
- Chafed, damaged, open, shorted wires within the cruise control harness
- Contaminated cruise control switch assembly (coffee, soda, juice, etc)
- Defective cruise control module
- Problem in the BCM (Body Control Module)
- Overheating parts causing malfunction
- Problems in the PCM (rare)
How to Check
First, check the cruise control switch/module, make sure the buttons and controls function properly. In many cases, buttons are missing, stuck in one position, or loose which is why it’s not making proper electrical connections. Dirt and particles that cause contamination can also lead to problems. Record all cruise control functions and their malfunctions or abnormalities.
If the cruise control light comes on in the instrument cluster when the cruise is manually activated, then it’s in good shape. If it does NOT, then verify if there’s a fuse. This information can be found in your vehicle’s service manual. Any blown fused must be replaced by a new and manufacturer-approved fuse.
Access the harness to the cruise control switch/module. In most cases, you would have to remove dash parts (steering column, steering wheel, airbag, etc.). To find the specific wire involved in the fault, you will need a proper wiring harness for your vehicle. This can vary significantly given many reasons. Again, refer to your service manual before executing this step.
Make sure your ABS (anti-lock brake system) is in good shape, and there are no ABS light on your dash. ABS uses multiple sensors including speed sensors, which if it’s malfunctioning, could fool the computer into thinking the vehicle is going faster or slower than the actual speed.
How to Fix
Depending on the diagnosis, common repair solutions include:
- Replacement of defective cruise control switch
- Repair of short or open circuits in the cruise control buttons
- Repair of open or shorted electrical wiring
- Repair of damaged cruise control system connectors
- Replacement of blown fuses
- Repair of underlying issue that caused the blown fuse
The severity of this code is considered low, as you can still use the vehicle even when the cruise control system loses its function. If left unaddressed, however, this code can lead to further electrical damage to the vehicle’s electrical system.
The most common mistake when addressing this code is not checking the cruise control on/off switch on the dash for short issues, as most people assume replacement of cruise control switches on the steering wheel can fix the problem.