Code
U1167
HUMMER
U — Network/User
Loss of serial communications for class 2 devices
AI status
Completed
Completed
100%
Causes
- Open or short in Class 2 serial data wiring or connector
- Corroded or loose connector or pin at a module or junction
- Failed module on the Class 2 network
- Poor or missing chassis/ground or battery connection
- Blown fuse or power supply issue to one or more modules
- Water intrusion or physical damage to wiring harness or module
Symptoms
- One or more modules report no communication or are unavailable via a scan tool
- Loss of functions controlled by modules on Class 2 (e.g., radio, HVAC, instrument cluster, remote keyless)
- Intermittent or frozen displays, erroneous or multiple unrelated warning indicators
- Unable to perform certain module-specific diagnostics or reprogramming
- Possible drivability or convenience issues if affected module controls engine or transmission functions
What to check
- Use a scan tool to read current/pending U- and B- codes and to see which modules are not responding
- Record freeze frame and network status data from the scan tool; note which modules report as offline
- Visually inspect Class 2 wiring, connectors, and harness routing near affected modules and junctions for corrosion, damage, or pin pushing
- Check fuses and power/ground circuits for modules on the Class 2 network
- Wiggle test harnesses and connectors while observing scan tool for changes in communication
- Measure voltage at module power pins and check ground integrity with a digital meter
Signal parameters
- Presence of serial data activity on Class 2 data line (bus toggling during communications)
- Idle line voltage level on Class 2 data circuit (should be stable when idle)
- Voltage supply and ground at affected module pins (battery voltage present and stable)
- Resistance/continuity of Class 2 wiring between modules and junction points
- Absence/presence of short to battery or ground on the Class 2 data line
Diagnostic algorithm
- Verify battery voltage and charging system are within specification; low voltage can cause communication faults.
- Connect a capable OEM-style scan tool and identify which modules are responding and which report lost communication. Note any additional U- codes.
- Inspect and clean connectors and grounds for modules that are not communicating. Secure any loose connections.
- Check all related fuses and power feeds to modules on the Class 2 bus; repair any open circuits.
- Perform a visual harness inspection and pin-backprobe power, ground, and data terminals at non-communicating modules. Repair damaged wires, bent pins, or corrosion.
- Use a lab scope or serial data diagnostic tool to observe the Class 2 data line for activity, noise, or waveform errors. If the line is quiet, isolate by disconnecting modules one at a time to identify a faulted module or short.
- If a specific module is identified as the source (no power, internal fault, or placing noise on bus), substitute with a known-good module if available or bench-test the module where possible.
- After repairs, clear codes and perform a full scan to confirm all modules are communicating and the U1167 does not return. Road test as required to verify intermittent faults are resolved.
Likely causes
- Corroded or loose connector at a module on the Class 2 bus
- Damaged wiring harness (open, short to ground or battery) in the Class 2 network
- Failed control module on the Class 2 bus (common modules: BCM, radio, HVAC, clusters)
- Poor ground or battery/fuse fault affecting module power or reference
Fault status
Status
Class 2 serial communication lost — one or more devices not responding on the network.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
Similar codes
Repair manuals
Manual library for HUMMER
138
Browse 138 HUMMER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.
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