Code
B1399
HUMMER
B — Body
Loss of KDD Communications
AI status
Completed
Completed
100%
Causes
- Faulty KDD control module
- Open or shorted wiring between KDD and vehicle data bus
- Poor or corroded connectors or grounds at the KDD module
- Loss of module power or ignition-switched supply
- Missing or incorrect bus termination/resistance
- Intermittent network interference or bus errors
Symptoms
- DTC B1399 recorded and lamp(s) may or may not be illuminated
- Features controlled by KDD inoperative (locks, switches, displays — manufacturer-specific)
- Other networked modules reporting communication faults
- Intermittent or permanent loss of related functions
- Possible vehicle-to-scan-tool communication problems for that module
What to check
- Confirm code with a factory-level scan tool and note freeze frame/related U-codes
- Check if the KDD module is present/listed on the network via scan tool
- Visually inspect connector at KDD for corrosion, bent pins, water ingress
- Verify fuses and relays supplying KDD power and ignition circuits
- Check module ground(s) for low resistance to battery negative
- Measure CAN/LIN bus voltages at the KDD connector with ignition ON
Signal parameters
- CAN bus idle voltages: CAN_H ≈ 2.5–3.5 V, CAN_L ≈ 1.5–2.5 V (both ~2.5 V recessive)
- CAN differential voltage when dominant: ≈ 1.0–2.5 V (depends on transceivers)
- Typical CAN high-speed bus termination ≈ 60 ohms (two 120 Ω ends in parallel)
- LIN bus idle: single-wire pulled to battery through resistor; expect near battery voltage when idle and pulses to ground when active (manufacturer dependent)
- Data bus speed: commonly 125 kbps (LIN) or 250/500 kbps (CAN) — verify exact bus for vehicle
Diagnostic algorithm
- Use a scan tool to read all DTCs and capture freeze frame and any related U-codes. Note whether the KDD module shows on the network.
- Clear codes, then key cycle and see if B1399 returns. If intermittent, record conditions when it sets.
- Inspect the KDD connector and harness for damage, corrosion, water intrusion, or aftermarket splices.
- Verify power and ground at the KDD module with a DVOM: battery positive with ignition ON, and low resistance ground to chassis.
- Probe CAN/LIN bus lines at the module with an oscilloscope if available. Confirm idle voltages, presence of periodic frames, and absence of excessive noise or shorts.
- Check bus termination resistance with power off. Replace missing or incorrect termination.
- If wiring appears good, disconnect the module and check for shorts to battery or ground on its harness pins.
- If harness and bus signals are normal but module not communicating, try swapping with a known-good module (if available) or bench-testing the module per manufacturer procedure.
- Reprogram or update module software if a software fix is available and the module hardware is otherwise functional.
- After repair, clear codes and verify full network communication and restored functions. Document repair and advise on warranty/TSB applicability.
Likely causes
- Disconnected or corroded connector at the KDD module
- Damaged CAN/LIN pair or spliced repair causing open/short
- Blown fuse or lost 12V/ignition feed to KDD
- Failed KDD module electronics
- Faulty network termination resistor or low-impedance short to chassis
Fault status
Status
Loss of KDD communications — module not responding or messages not present on the vehicle data bus.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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Repair manuals
Manual library for HUMMER
138
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