U0073 Code (Symptoms, Causes and How to Fix)

U0073 is a generic diagnostic code that will be set by the OBD2 diagnostic system in your automobile or light truck for specific types of CAN-bus System malfunctions. CAN which stands for Controller Area Network is the standard computer network communication system within your vehicle’s control network (or bus).

Systems in your vehicle utilizing CAN-bus include the ECU (Engine Control Unit) or PCM (Powertrain Control Module), the ABS (Anti-lock Braking System Module) and the TCM (Transmission Control Module).

Here’s everything you need to know about a U0073 code, including its symptoms, causes, and how to fix it.

U0073 code

What Does Code U0073 Mean?

OBD-II Trouble Code U0073 Description
Control Module Communication Bus "A" Off

This means that the primary CAN-bus controller has detected an intermittent or permanent failure (open circuit) in communication through a related cable or at any one or more of the many modules on the system.

Such a failure in digital communication can cripple or confuse the operation of one or more of the inter-related vehicle systems. This can result in a multitude of peculiar problems as evidenced by these example symptoms.

Related: DTC U0001, DTC U0100, DTC U1000

How Does the CAN-bus System Operate?

car wiring system

The CAN-bus system actually links together most if not all of the electronic devices and modules in your vehicle. Some of these systems and modules are interdependent and need inter-related digital communications to function properly.

Other systems, independent of one another, need to furnish operating characteristics to the PCM in order to provide status information to the driver via the instrument panel.

A simple example of such a system is the car’s array of exterior lights, including the headlights, tail lights, side marker lights, brake lights and turn signal lights. CAN-bus enables each of these lamps to report normal operating status to the instrument panel as well as failure information to that same display.

While this could be done with multiple wires to each of these lights, CAN-bus enables digital codes to be sent through as few as the two power wires to each lamp giving full operational commands to that lamp and also return operational status of that lamp to the PCM to be used as needed.

Because CAN-bus communicates operational information to each lamp and sends back status information in digital code along the common power wires, the need for multiple wires is eliminated saving cost, weight and wiring complexity.

This works well when the system has complete electrical continuity. When continuity failures occur, inter-communication is interrupted. This is where the error code U0073 comes into play.

Symptoms of Code U0073

dash warning lights

The following list of possible symptoms may occur when this code is set by the OBD2 system:

  • Instrument panel warning lights may flicker on and off.
  • Transmission may not shift or may default to and remain in 2nd gear.
  • Door locks may cycle intermittently.
  • Engine may intermittently fail to crank or not start at all.
  • Instrument panel gauges may operate erratically.
  • Application of brakes may cause erratic instrument panel indications and/or chimes to sound.
  • Various other erratic system problems too numerous to list.

Causes of Code U0073

bad body control module symptoms
Body Control Module (BCM)

Here is a list of some of the possible causes for this OBD Code:

  • Unseated connector at one or more of the system modules.
  • Backed out pin or pins in one or more CAN-bus cable connectors.
  • CAN-bus cable insulation frayed causing a short to ground.
  • Severed CAN-bus cable.
  • Corrosion at one or more of the CAN-bus cable connectors.
  • Moisture entry to one or more of the CAN-bus cable connectors or modules.
  • One or more system control modules with electrical problems.
  • Other electrical problems that are interfering with proper CAN-bus continuity.

Is Code U0073 Serious?

Yes, this code could be serious at worst or just annoying at best. It would depend on which system or systems are affected by the CAN-bus discontinuity.

The problem could be as simple as a failure of a power window to roll up or down. Or it could be as serious as the ABS (Anti-lock Braking System) failing to properly modulate your brakes when needed during a panic stop.

It could be expected that the U0073 Code would be accompanied by additional system warnings or OBD2 codes if automobile safety systems are compromised. However, depending on such warnings to be operative when an U0073 Code occurs would not be wise. When this code is set, immediate corrective action is very strongly recommended.

How to Fix Code U0073

best automotive diagnostic scanner

Fixing problems related to this code can be extremely difficult since the electrical issues may neither be visually apparent nor may they be easily diagnosed.

First, an in-depth knowledge of the complete CAN-bus system, its cable routing, related interfaces and modules is required. Then, appropriate electronic diagnostic tools would be needed to identify the electrical deficiencies.

It is possible that a capable DIYer could identify a broken or worn through wire in a cable bundle to be the cause of this problem. Then a repair could be made.

However, the often circuitous routing of the many cables in your vehicle would make such an evaluation survey difficult to conduct and to correct. And a loss of continuity inside any of the many modules in the car would be far more difficult to diagnose.

For these reasons, diagnosing and repairing problems related to this code should best be handed off to a competent dealer service department or an automotive electrical diagnosis and repair service.

Ron Coddington

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