U007D

Code

Generic U — Network/User

Control Module Communication Bus K Off

Brand: Generic

Type: U — Network/User

Views: UK: 22 EN: 180 RU: 25

AI status

Completed

ready

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Page language: EN

Causes

Open or shorted K-line wiring/connector
Failed or unpowered control module on the K bus
Blown fuse or loss of ignition-switched power to network modules
Poor or missing ground(s)
Corroded or damaged connector pins
Aftermarket device or recent repair that disturbed wiring

Symptoms

Some or all modules on the K bus not responding to a scan tool
Multiple system malfunctions (body/comfort, immobilizer, dash instruments)
Vehicle fails to recognize key or remote functions
MIL illuminated with related communication DTCs
Intermittent module operation or loss of features after start

What to check

Connect a scan tool and confirm U007D and any other communication codes; note which modules are non-responsive
Check battery voltage and ignition-switched power (key ON) at main fuses and module power feeds
Inspect fuses related to instrument/body/network power and replace if blown
Visually inspect K-line wiring, harnesses, and connectors for damage or corrosion
Backprobe K-line at suspected modules and measure voltage/continuity
Wiggle wiring and connectors while monitoring network to reproduce intermittent faults

Signal parameters

K-line idle voltage with ignition ON (should be near battery voltage through pull-up)
Voltage drop to ground when a module transmits (lowing the line briefly)
Continuity/resistance of K-line to module connectors (low/near 0 ohms for short, open >infinite)
Presence/absence of serial data activity using a lab scope or dedicated communication tester
Scan tool detection of module IDs and message frequency when bus is functioning

Diagnostic algorithm

Record exact conditions (key position, recent repairs, intermittent vs permanent). Note all related DTCs and non-responsive modules.
Verify battery is fully charged and stable. Low battery can cause network modules to drop offline.
Check and restore any blown fuses or removed fusible links that supply network modules.
Perform a visual inspection of main harnesses, gateway connector, and modules for damage or corrosion.
Using a DVOM, check for K-line voltage at the module connector with key ON; compare to expected idle voltage. If no voltage, trace power/pull-up path to its source.
If voltage present but no data, use an oscilloscope or data logger on the K-line to look for serial frames or a module pulling the line low. If noisy or stuck low, isolate modules by disconnecting them one at a time to find the faulting unit.
Check continuity of K-line between the scan tool connector and each module. Repair opens or shorts found, then retest.
Inspect and repair grounds and power feeds to any non-responsive modules. Reconnect and clear codes; attempt communication again.
If a specific module removal isolates the fault (bus returns), test or replace the suspect module per manufacturer procedures.
After repairs, clear codes and verify normal communication under various conditions (key cycles, engine run, accessory operations).

Likely causes

Disconnected/loose connector at a control module on the K bus
Blown ignition or module power fuse feeding the network
Single module pulling the bus down due to an internal fault
Damaged harness (chafing, rodent damage) interrupting the K-line
Corroded pin(s) at main junctions (gateway/module harness)

Fault status

⚠️ Status

Communication Bus 'K' Off — the vehicle controller detected that the K communication bus is inactive or modules on that bus are not communicating. Investigate wiring, power/ground, and modules on the K-line.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-3 hours