U0024

What it means

U0024 is the generic SAE J2012 code for an open circuit on the low speed CAN communication bus (-) line (CAN Low). A control unit monitoring the network has detected that the CAN Low wire is not continuous, or that its signal is missing, so messages on the low speed bus cannot be exchanged reliably. The affected bus, and which modules are on it, depends on the model and its network layout.

Symptoms

• Warning lights on the dashboard, possibly several at once
• Body electrical functions failing or acting erratically, such as central locking, windows, mirrors or lighting
• Instrument cluster gauges or displays not working or showing messages about missing communication
• Scan tool unable to communicate with one or more modules
• Intermittent faults that come and go with vibration or temperature
• Battery drain if modules fail to go to sleep

Possible causes

• Open circuit, broken wire or chafed CAN Low wiring in the low speed bus harnesslikely
• Corroded, loose or pushed-back terminals in a connector on the bus, often at door hinges, boot loom or under seatslikely
• Water ingress or damage at a splice point or junction connector on the networkpossible
• Faulty control module on the bus with a failed internal CAN Low driver or connectionpossible
• Poor power or earth supply to a module on the bus causing it to drop out of communicationpossible
• Previous repair or accessory fitting that damaged or incorrectly spliced the network wiringrare

How to diagnose

1. Read all stored codes from every module and record freeze frame data, noting which modules report lost communication to help locate the break
2. Check battery condition and charging voltage, as low voltage can cause spurious network faults
3. Visually inspect the wiring and connectors for the low speed bus for damage, corrosion, water ingress, and signs of past repairs or aftermarket accessories
4. Use the manufacturer wiring diagram to identify the bus layout, the modules on it and the junction or splice points, as this varies by model
5. Wiggle test the harness and connectors while monitoring communication with a scan tool to find an intermittent break
6. With the battery disconnected as per procedure, test the CAN Low wire for continuity and for short to earth or supply between modules, and check terminating resistance where the layout specifies it
7. Unplug modules one at a time, following the manufacturer procedure, to see whether a faulty module is affecting the bus
8. Check power and earth supplies to the modules that have lost communication

How to fix

• Repair or replace the damaged section of CAN Low wiring, using a proper soldered and sealed repair rather than twisting wires together
• Clean, repair or replace corroded or damaged connectors and terminals
• Dry out and repair any water-affected connector or splice, and fix the source of the leak
• Replace a confirmed faulty control module and have it programmed or coded as required by the manufacturer
• Repair poor power or earth connections to the affected modules

Can I keep driving?

Nearby codes

• U0023GenericLow Speed CAN Communication Bus (+) High
• U0025GenericLow Speed CAN Communication Bus (-) Low