High Speed CAN Communication Bus (-) Open

What U0006 means

U0006 is a generic SAE J2012 network (U) code. The high-speed CAN bus is the vehicle's primary data backbone, on many designs a 500 kbit/s network that links the powertrain, brakes, cluster, gateway and other control modules. Those modules connect in parallel to a twisted pair of wires: CAN-High, the bus (+) line, and CAN-Low, the bus (-) line. Twisting the pair shields the low-voltage signals from electromagnetic interference. A pair of 120-ohm terminating resistors, usually built into the bus star connectors, sits at the ends of the network so a healthy bus measures roughly 60 ohms across the two wires with the battery disconnected. U0006 sets when the monitoring module sees an open in the CAN-Low conductor rather than a short or invalid data. When that wire breaks, one or more modules can be isolated from the rest of the bus. An isolated module still tries to transmit but cannot receive messages or win arbitration, and each attempt disturbs the voltage on the surviving wire, corrupting traffic for the whole network. Because so many systems share this bus, a single CAN-Low open often triggers a cluster of lost-communication U-codes across several modules at once.

Symptoms

• Several warning lights on together (check engine, ABS, traction/stability, airbag, and others)
• Multiple modules unresponsive, with lost-communication U-codes stored across the vehicle
• Scan tool cannot establish communication with one or more control modules
• Engine may crank but not start, or the vehicle drops into a reduced-power limp mode
• Gauges, warning indicators, or driver aids behave erratically or stop working

Common causes

• Open, broken, or corroded CAN-Low (bus -) wire somewhere along the high-speed bus run
• Backed-out, spread, or corroded terminal at a module or bus star connector on the CAN-Low pin
• Water intrusion at a connector or splice raising resistance until the CAN-Low path opens
• A damaged terminating resistor inside a star connector, showing up as high bus resistance
• A failed module that has dropped off the bus and is dragging or opening the network
• Harness damage from chafing, rodent bites, or a previous repair that broke the twisted pair

Severity & driving advice

Severity: High — A CAN-Low open can drop several modules off the high-speed bus, disabling driver aids and sometimes preventing the engine from starting.

Can I drive? Often drivable but risky; may not start. Fix promptly.

Diagnostic approach

1. Scan all modules and map the fault — Use a full-system scan tool, not a basic reader, and pull codes from every module. Note which modules report U0006 and which companion lost-communication U-codes appear. A group of modules that all fall silent together points to a single break in the shared CAN-Low line rather than a fault in each module.
2. Inspect connectors and harness on the bus — Using the wiring diagram as a guide, check the related splices, star connectors, and module connectors for water intrusion, corrosion, pushed-out or bent terminals, and correct pin tension. Wiggle-test suspect sections while watching for communication dropping in and out. Repair any damaged pins or wiring before further testing.
3. Measure bus termination resistance — Disconnect and isolate the negative battery cable, then measure resistance between the CAN-High and CAN-Low wires. A healthy high-speed bus reads about 60 ohms (roughly 53 to 67 ohms). A reading well above that range confirms an open or high resistance in the CAN-Low or CAN-High circuit between the star connectors, or a damaged internal terminating resistor.
4. Isolate the open by bus section — Use the star connectors to split the network into segments and re-measure resistance, narrowing down which branch contains the open CAN-Low conductor. Disconnecting modules one at a time also helps: if the resistance or communication returns to normal when a module is unplugged, that module or its branch is the fault. Trace and repair the broken conductor once the section is identified.
5. Repair, clear, and verify — Repair the open circuit or replace the damaged connector, terminal, or terminating resistor as needed. If a module is confirmed to be dropping the bus after wiring checks pass, replace and program it per the service procedure. Clear the codes, cycle the ignition, and confirm U0006 and its companion codes do not return after a road test.

Make & model notes

Jeep: On Stellantis vehicles (Jeep, Chrysler, Dodge, Ram) the high-speed bus is the 500K CAN-C network, with the Body Control Module acting as the central gateway between CAN-C and the slower interior bus. Terminating resistors are integral to the CAN-C star connectors, so the factory approach is to disconnect the battery, confirm the pair reads roughly 53.5 to 67 ohms, then use the star connectors to isolate the branch holding the open CAN-Low wire.

Ford: On Ford applications the modules communicate over the high-speed CAN network, and a CAN-Low open typically isolates one or more nodes and sets lost-communication codes across the vehicle. Confirm module power and grounds, verify continuity of the CAN-Low conductor between connectors, and check bus termination before condemning any control module.

FAQ