U1073 – Bus-Off (Mitsubishi)


By Reinier (Contact Me)
Last Updated 2020-08-13
Automobile Repair Shop Owner

Trouble CodeFault LocationProbable Cause
U1073 Bus-Off (Mitsubishi)
SCP (J1850) Invalid or Missing Data for Engine Coolant (GM)
SCP (J1850) Invalid or Missing Data for Engine Coolant (Ford)

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What Does Code U1073 Mean?

OBD II fault code U1073 is a manufacturer-specific trouble code that is defined by carmaker Mitsubishi as “CAN data bus – bus off, malfunction detected (Mitsubishi) — Pending”, and is sometimes set when the PCM (Powertrain Control Module) detects some types of failures in itself. More commonly though, this code sets when the PCM detects a break in one or more CAN (Controller Area Network) bus serial communications systems that have the potential to prevent effective communication between the PCM and one or more control modules over one or more communications networks in the vehicle.

As a practical matter, the several dozen control modules in a modern vehicle are interconnected by complex networks that are made up of thousands of circuits. These networks are collectively known as the CAN bus system but note that modern CAN bus systems are made up of several, discrete networks that connect different classes of control modules. In practice, and although the overarching CAN bus system connects all control modules, not all subsystems can communicate with each other.

Moreover, while the PCM acts as a sort of clearinghouse for data transmissions to and from all control modules, communication speeds over some networks are much higher than they are in other networks. One example is that data about (among other control functions) ignition timing, fuel delivery, and fuel control is communicated over one dedicated, high-speed network, while data about, for instance, climate control and seat adjustments are transmitted over another, slower network.

Additionally, different networks use different communications protocols, which greatly increase the overall complexity of modern CAN bus systems, and as a result, PCMs have a limited ability to tolerate faults in any part of the overarching CAN system. Therefore, if any fault, defect, failure, or malfunction in any part of the CAN system occurs that has the potential to prevent effective communication between control modules, the PCM will recognize that it cannot control or monitor parts of the CAN bus system reliably and/or effectively, and it will set code U1073 as a result. Note though that in some failure modes, a PCM might be unable to set and store trouble codes, which effectively means that sometimes, a failed PCM cannot record its own demise.

Where is the U1073 sensor located?

This image shows the location of the ECU on a late model Mitsubishi Pajero. Note though that while this location is almost universal on most Mitsubishi applications, the exact location of PCMs on Mitsubishi vehicles vary somewhat behind the dashboard. Consult reliable service information on steps to remove dashboard trim panels to gain access to the ECU without damaging the dashboard.

What are the common causes of code U1073?

Most causes of ECU and/or CAN (Controller Area Network) bus serial communications failures on Mitsubishi applications are many and varied, but, but could include one or more of the following-

  • Abnormal system voltages
  • Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors almost anywhere in one or more serial communication systems
  • Incorrect jump-starting procedures
  • Charging system defects and/or failures that cause severe voltage spikes
  • Although ECU failure is a rare cause for almost all other trouble codes, failed or failing ECU’s are among the leading causes of code U1073 on Mitsubishi applications

What are the symptoms of code U1073?

Common symptoms could include one or more of the following, depending on the exact nature of the problem-

  • Vehicle may have a no-start condition
  • Vehicle may be hard or difficult to start
  • Instruments may be frozen in the positions they were in when the failure occurred
  • Vehicle may be immobilized completely, in which case it may not be possible to extract fault codes
  • ECU may be unable to communicate with dealer-grade scan tools, but note that some generic code readers may produce false or ghost codes that may be misleading

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