U0002

What it means

U0002 is the generic SAE J2012 code for a performance fault on the high speed CAN communication bus. One or more control units detected that messages on the bus were corrupted, intermittent, out of range or showing too many errors, even though the bus was not completely lost. It is a network fault, so the cause is often a wiring, connector, power supply or module problem rather than a single failed part.

Symptoms

• Multiple warning lights on at once, such as engine, ABS, airbag or traction control
• Instrument cluster gauges dropping to zero or behaving erratically
• Intermittent loss of communication with one or more modules during scanning
• Engine running in a reduced power or limp mode
• Starting problems or a no-start in some cases
• Other U-codes stored in several modules

Possible causes

• Damaged, chafed, corroded or water-affected CAN wiring or connectors (CAN High or CAN Low)likely
• Low battery voltage, poor battery or earth connections, or an unstable power supply to moduleslikely
• A faulty control unit disrupting the bus by sending corrupted messages or pulling the lines downpossible
• Incorrect, damaged or missing terminating resistance on the bus (open or shorted termination, or a faulty module containing a terminating resistor)possible
• Poorly fitted or badly installed aftermarket electrical equipment such as alarms, trackers or radios tapped into the networkpossible
• Outdated or faulty software in a control unit that is a known cause of bus errors on that modelrare
• Previous accident or water damage affecting a wiring harness or junction connectorrare

How to diagnose

1. Read all stored codes from every module and record freeze frame data, noting which modules report U-codes and which do not, as this helps to locate the fault in the network
2. Check battery condition and charging voltage, and inspect battery terminals and main earth points for tightness and corrosion
3. Look for any aftermarket equipment connected to the network or diagnostic socket and disconnect it for testing if practical
4. Visually inspect CAN wiring, junction connectors and module connectors for damage, moisture, corrosion or pushed-back pins, using the manufacturer wiring diagram for the model
5. Clear the codes and see whether U0002 returns immediately or only intermittently, wiggling harnesses and connectors while monitoring communication
6. With the ignition off and battery disconnected, measure the resistance between CAN High and CAN Low at the diagnostic socket and compare with the specified value for the vehicle, which depends on the model
7. Check CAN High and CAN Low voltages or view the signal on an oscilloscope to find shorts, open circuits or noise
8. Isolate suspect modules one at a time following the manufacturer procedure to see whether the bus signal returns to normal

How to fix

• Repair or replace damaged wiring, terminals or connectors on the CAN bus, sealing against moisture
• Restore good power and earth supply by charging or replacing the battery and cleaning or tightening connections
• Replace or repair a faulty control unit found to be disrupting the bus, with coding or programming as required by the manufacturer
• Correct the bus termination fault by repairing the wiring or replacing the affected module
• Remove or properly rewire faulty aftermarket equipment
• Update control unit software only where the manufacturer lists it as a fix for the fault

Can I keep driving?

Nearby codes

• U0001GenericHigh Speed CAN Communication Bus
• U0003GenericHigh Speed CAN Communication Bus (+) Open