U0104 Lost Communication With Cruise Control Module

The diagnostic trouble code U0104 – Lost Communication With Cruise Control Module means that a vehicle control module has stopped receiving the expected communication messages from the Cruise Control Module.

This is a communication-related DTC, not a direct diagnosis of a defective cruise-control switch, steering-wheel button, brake switch, or cruise-control actuator.

Modern cruise-control systems are integrated with several electronic modules. Depending on the vehicle, cruise-control information can be exchanged between the engine control module, transmission control module, body control module, steering controls, instrument cluster, and other systems through the vehicle's communication network.

When the expected messages from the cruise-control module disappear, U0104 may be stored.

What Is the Cruise Control Module?

The exact design varies considerably between manufacturers.

On some vehicles, cruise-control functions are handled by a dedicated module. On others, the cruise-control logic may be integrated into the ECM, BCM, steering-column electronics, radar/ADAS system, or another control unit.

A dedicated cruise-control module, where fitted, can process information such as:

• Vehicle speed

• Driver cruise-control commands

• Accelerator position

• Brake-pedal status

• Clutch-pedal status on manual-transmission vehicles

• Engine operating conditions

• Transmission status

• Distance information on adaptive systems

• Safety-system status

It can then exchange the relevant information with other modules.

Because of this integration, a communication failure can disable cruise control even when the engine and transmission themselves are operating normally.

What Does U0104 Actually Tell You?

U0104 tells you that the expected communication with the cruise-control module was lost.

It does not tell you exactly why.

The underlying problem could be:

• Cruise-control module power loss

• Poor module ground

• Blown fuse

• Damaged CAN wiring

• Connector corrosion

• Loose electrical terminals

• Shorted communication circuit

• Open communication circuit

• Network interference from another module

• Low battery voltage

• Internal module failure

• Software or configuration problem

This distinction matters because replacing a cruise-control component without checking the communication network can easily result in an unnecessary repair.

How Cruise Control Communicates With the Vehicle

Most modern vehicles use a communication network such as CAN (Controller Area Network) to exchange information between electronic control units.

Cruise control may need information from several systems before it can safely maintain a selected speed.

For example, the system may need to know whether:

• The brake pedal is being pressed.

• The clutch is being pressed.

• The accelerator is being used.

• The vehicle speed is valid.

• The engine is operating correctly.

• The transmission is in an appropriate state.

• Stability-control intervention is occurring.

• Another safety system has requested cruise-control cancellation.

This information can be shared electronically rather than through separate dedicated wires for every function.

If communication is lost, the system may disable cruise control as a precaution.

Symptoms of U0104

The most obvious symptom is often that cruise control does not operate.

Possible symptoms include:

• Cruise control unavailable

• Cruise-control warning light

• Cruise-control message on the instrument cluster

• Cruise-control buttons not responding

• Adaptive cruise control unavailable, where equipped

• Stored communication codes

• Intermittent cruise-control operation

• Multiple warning lights in some vehicles

In many cases, the vehicle can still be driven normally without cruise control.

However, if U0104 occurs together with other communication faults, the situation may involve a larger network problem.

Why the Engine May Still Run Normally

Cruise control is generally not required for basic engine operation.

The accelerator pedal can still control engine torque normally, and the transmission can continue functioning independently.

Therefore, a vehicle can have U0104 while:

• Starting normally

• Idling normally

• Accelerating normally

• Shifting normally

• Braking normally

The main visible consequence may simply be the loss of cruise-control functionality.

This is one reason communication codes can sometimes be overlooked even though they still require diagnosis.

Common Causes of U0104

Loss of power to the cruise-control module

If the module loses its electrical supply, it cannot communicate.

Possible causes include:

• Blown fuse

• Damaged wiring

• Failed relay

• Loose terminal

• Corroded connection

• Ignition-power problem

The vehicle-specific wiring diagram should be used to identify every relevant power supply.

Poor ground

A weak or corroded ground can cause a module to operate incorrectly or disappear from the communication network.

Ground integrity should be tested under appropriate load conditions rather than relying only on a simple continuity test.

CAN network problem

A damaged CAN circuit can interrupt communication between the cruise-control module and the rest of the vehicle.

Possible faults include:

• Open circuit

• Short to ground

• Short to power

• Short between CAN lines

• Damaged wiring

• Corroded terminals

• Poor connector contact

Connector damage

Cruise-control-related modules and wiring can be located in areas exposed to vibration, moisture, heat, or previous repair work.

Look for:

• Water intrusion

• Corrosion

• Bent pins

• Loose terminals

• Pushed-back terminals

• Broken connector locks

• Evidence of overheating

Low system voltage

A weak battery or charging-system problem can cause electronic modules to reset or temporarily disappear from the network.

If U0104 appeared after:

• A weak battery

• Jump-starting

• Battery replacement

• Very slow cranking

• Electrical repairs

the vehicle's power supply should be investigated.

Internal module failure

The cruise-control module itself can fail.

Electronic components can be affected by:

• Heat

• Moisture

• Vibration

• Voltage spikes

• Internal component failure

But an internal module failure should generally be considered only after power, ground, wiring, connectors, and network communication have been checked.

U0104 Does Not Automatically Mean the Cruise-Control Switch Is Bad

The buttons on the steering wheel or dashboard are often blamed when cruise control stops working.

However, U0104 specifically concerns communication with a module.

A faulty cruise-control switch can certainly cause cruise-control problems, but it does not automatically explain a lost-communication DTC.

The switch and its wiring should be investigated when the diagnostic data points in that direction.

A Logical Diagnostic Process

A good diagnosis begins with a complete vehicle scan.

Do not limit the inspection to the module that initially displayed U0104.

Read all available DTCs from:

• ECM/PCM

• TCM

• BCM

• ABS/ESC

• Instrument cluster

• Cruise-control-related modules

• ADAS modules where applicable

If several modules report communication problems, this may point toward a common network or power-supply problem.

Determine Whether the Cruise-Control Module Is Accessible

One of the most useful diagnostic questions is:

Can the scan tool communicate with the cruise-control module?

If the module responds normally, the technician should investigate why another module recorded a communication loss.

An intermittent network problem, communication timing issue, wiring problem, or software-related condition may be involved.

If the module cannot be accessed at all, attention should shift toward:

• Module power

• Module ground

• Fuses

• CAN wiring

• Connectors

• Module condition

Check the Battery and Charging System

Before performing detailed CAN diagnosis, verify that the vehicle has a stable electrical supply.

A low-voltage event can create several U-codes at the same time.

Do not rely on a universal “normal voltage” rule for every test. Follow the manufacturer's specifications and consider battery condition, cranking voltage, charging behavior, and voltage stability.

Inspect Fuses and Power Supplies

Locate the fuses associated with the cruise-control system using the correct vehicle documentation.

Some vehicles may have multiple power feeds.

A fuse should not simply be replaced repeatedly without finding out why it failed.

If the replacement fuse blows again, there may be a short circuit or another electrical problem.

Check the Module Ground

A proper ground is essential for reliable module operation.

A technician should verify:

• Ground continuity where appropriate

• Ground voltage drop under load

• Ground terminal condition

• Ground connection to the vehicle body or powertrain

A visually clean ground connection can still have excessive electrical resistance.

Inspect CAN Wiring

If power and ground are correct, the communication network should be checked according to the manufacturer's diagnostic procedure.

Depending on the vehicle, this can involve checking:

• CAN circuit continuity

• Shorts to ground

• Shorts to power

• Shorts between network circuits

• Network termination

• Communication activity

• Connector integrity

There is no single universal CAN measurement that applies to every vehicle. Network architecture and specifications vary.

Look at Freeze-Frame and Fault History

If the scan tool provides freeze-frame or fault-history information, examine it carefully.

Useful information can include:

• Vehicle speed

• Engine speed

• Battery voltage

• Ignition status

• Brake status

• Clutch status

• Other active DTCs

• Whether the fault was current or stored

An intermittent U0104 that occurred only during a low-voltage event is a different diagnostic situation from a cruise-control module that remains permanently offline.

U0104 and Brake or Clutch Switch Problems

Brake and clutch switches are important to cruise-control operation.

Cruise control normally cancels when the driver presses the brake pedal, and manual-transmission vehicles may also cancel when the clutch is operated.

However, a defective brake or clutch switch would generally create a different diagnostic direction from a pure communication loss.

If U0104 is accompanied by brake-switch, clutch-switch, vehicle-speed, or communication codes, all of those codes should be evaluated together.

Adaptive Cruise Control Changes the Diagnosis

Vehicles equipped with Adaptive Cruise Control (ACC) can have a considerably more complicated architecture.

ACC may interact with:

• Radar sensors

• Cameras

• ABS/ESC

• ECM

• TCM

• Steering systems

• Body control systems

• ADAS modules

A communication problem involving one of these systems may cause cruise control to become unavailable.

Therefore, on an ACC-equipped vehicle, U0104 should be diagnosed using the manufacturer's complete network and ADAS documentation rather than treating it as a simple conventional cruise-control fault.

Intermittent U0104

An intermittent communication problem can be especially frustrating.

Cruise control may work perfectly for several days and then suddenly become unavailable.

Possible causes include:

• Loose connector

• Poor terminal tension

• Corrosion

• Water intrusion

• Wiring damage

• Vibration-sensitive connection

• Temperature-sensitive module fault

• Battery-voltage instability

• Intermittent CAN fault

If the fault appears after driving over rough roads, after heavy rain, or only when the vehicle is hot, those conditions can be valuable diagnostic clues.

Can U0104 Affect Vehicle Safety?

The immediate effect is often limited to loss of cruise-control functionality.

However, cruise control is integrated with other systems on many modern vehicles. If U0104 appears alongside ABS, ESC, steering, transmission, or other communication codes, the overall situation can become more significant.

If multiple warning lights appear or the vehicle develops abnormal braking, steering, engine, or transmission behavior, it should be diagnosed before continued driving.

Should the Cruise Control Module Be Replaced?

Not based on U0104 alone.

Before condemning the module, verify:

• Correct power supply

• Correct ground

• Fuse condition

• Connector condition

• CAN communication circuits

• Network integrity

• Battery and charging condition

• Other module communication

• Manufacturer-specific module tests

If all external circuits are confirmed good and the cruise-control module remains inaccessible or fails its internal diagnostic tests, module failure becomes a much stronger possibility.

Depending on the vehicle, a replacement module may require programming, configuration, calibration, or initialization.

A Useful Way to Think About U0104

U0104 is essentially asking you to find out why the vehicle can no longer hear from the cruise-control module.

The diagnostic path should therefore progress from the simplest possibilities toward the more complex ones:

Power → Ground → Fuses → Connectors → CAN wiring → Network → Module

At the same time, all other stored communication codes should be considered because they may reveal a common cause.

The code itself does not prove that the cruise-control module has failed, nor does it prove that the cruise-control switch or another individual component is defective.

Once communication is restored, the cruise-control system can be tested again to determine whether there is a separate functional problem.