Code
U1166
HUMMER
U — Network/User
Loss of Communications with SCM
AI status
Completed
Completed
100%
Causes
- Open, shorted or corroded wiring/connector at the SCM
- Faulty SCM (internal failure)
- Blown fuse or missing power/ground to the SCM
- CAN/LIN bus wiring fault (short to battery/ground or high resistance)
- Failed network termination or bus interference from aftermarket device
- Intermittent battery/low voltage condition or weak charging system
Symptoms
- Inability to communicate with SCM using scanner (no response)
- Steering-column related functions inoperative (e.g., steering wheel switches, column lock, shift/interlock — vehicle-specific)
- Multiple network/comms DTCs stored in other modules
- MIL (Check Engine) or network-related warning messages on dash
- Intermittent loss of features or intermittent DTC appearance
What to check
- Retrieve and record all U-codes and any related freeze frame data with a scan tool
- Check battery voltage and charging system (stable >12V with key on)
- Inspect SCM connector(s) and wiring for corrosion, bent pins, water intrusion or physical damage
- Verify fuses and module power/ground circuits for proper voltage and continuity
- Check for other modules reporting network faults (helps isolate bus segment)
- Measure CAN/LIN bus voltages and termination resistance at known good nodes
Signal parameters
- CAN_H/CAN_L idle differential ~0V common-mode ~2.5V (individual lines ~2.5V each) — expect ~2.5V on each line with ignition on
- Typical high-speed CAN bus differential amplitude ~2V (varies by system); baud rate commonly 250 kbps or 500 kbps depending on vehicle
- Proper termination resistance = ~60 ohms measured across CAN_H to CAN_L at two-wire high-speed CAN segment
- LIN bus idle ~ battery voltage on LIN, single-wire communication pulses to ground (if SCM uses LIN)
Diagnostic algorithm
- Use scan tool to confirm U1166 present; record time-stamped and related codes from all modules.
- Attempt to communicate directly with SCM using manufacturer-level scanner. Note whether module is responsive intermittently or not at all.
- Check battery voltage with key on and during starter cranking. Recharge or stabilize battery if low before further testing.
- Visually inspect SCM connector(s) and harness at the steering column for corrosion, water, chafing or damage. Repair any damaged wiring/terminals.
- Verify SCM power and ground circuits: back-probe connector with key on; compare to wiring diagram for pin functions. Repair open/poor connections.
- Check related fuses and relays for continuity and proper operation; replace if open.
- Measure CAN bus voltages at SCM connector and at another known good node: confirm ~2.5V on each conductor and ~60 ohms across CAN_H to CAN_L. Look for short to battery or ground.
- If bus voltages or termination are incorrect, isolate the segment by disconnecting connectors and retesting to locate short/high resistance. Repair wiring or connectors as required.
- If wiring and bus integrity are good but SCM still does not communicate, check for intermittent faults by wiggling harnesses while monitoring communication; use lab scope to view data frames if available.
- If module failure is suspected after verifying power, ground and bus integrity, follow manufacturer procedure for SCM replacement and programming/reflashing. Clear codes and retest.
- After repairs, clear codes, perform functional tests for column-related features and road test to confirm the fault does not return.
Likely causes
- Corroded or loose connector at SCM (common on column area)
- Broken or chafed CAN/LIN data wires between SCM and network
- Blown fuse or poor ground at the module
- Failed SCM module
- Network termination or short to power/ground on data bus
Fault status
Status
No valid network messages received from SCM — communication fault (intermittent or permanent). Verify wiring, power/ground and CAN/LIN bus integrity before replacing module.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 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.
HUMMER
-
HUMMER: 2009
-
HUMMER: 2008
-
HUMMER: 2007
-
HUMMER: 2005
-
HUMMER: 2004
-
HUMMER: 2000
-
HUMMER: 1999
-
HUMMER: 1994
-
HUMMER: 1993
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email