Code
U1016
HUMMER
U — Network/User
Loss of Class 2 Communication with VCM
AI status
Completed
Completed
100%
Causes
- Blown fuse or loss of VCM power/ignition feed
- Poor or missing ground at the VCM or common chassis ground
- Open, shorted or corroded Class 2 network wiring or connector(s)
- Corroded/damaged VCM connector pins or water intrusion
- Failed VCM/module or internal module fault
- Aftermarket accessory or module interfering with the Class 2 bus
Symptoms
- Scan tool shows "No Communication" or cannot connect to VCM
- Multiple unrelated DTCs or a network-related DTC set
- Malfunctioning or disabled vehicle systems that rely on the VCM
- Instrument cluster warnings or ignition/starter interlocks
- Intermittent operation of features (cruise, transmission shifts, etc.)
What to check
- Confirm U1016 present and check Freeze Frame/related DTCs and timestamps
- Verify battery voltage is within specification (key on and cranking)
- Check fuses and power circuits for VCM and related modules
- Visually inspect VCM connector and Class 2 wiring for damage, corrosion, or water entry
- Attempt to communicate with other modules on the Class 2 bus to determine scope of loss
- Disconnect aftermarket accessories that tie into the data bus and retest
Signal parameters
- Class 2 network: expect serial data activity on the data wire when ignition ON — absence indicates open/short
- Idle/steady voltage level and pulse transitions should be present; check with a scope or manufacturer-approved bus monitor
- Compare waveform or activity count to a known-good vehicle or factory specification using a lab scope/scan tool
- Observe for noise, missing frames, long pauses, or stuck-high/low conditions on the bus
Diagnostic algorithm
- Record all stored codes and freeze frame data. Note when the DTC sets and any relationship to vehicle symptoms.
- Attempt normal communications with the VCM using a factory scan tool. Confirm "no response" or intermittent response.
- Verify battery voltage (12.4–12.8 V nominal with engine off; >13 V when running). Repair battery/charging issues first.
- Inspect and test fuses and power feeds to the VCM; restore any blown/missing circuits and retest communication.
- Visually inspect the VCM connector and harness for corrosion, bent pins, water intrusion or physical damage; repair as needed.
- Backprobe the Class 2 data wire at the VCM connector and check for data activity with a scope or data bus monitor while key is ON. If no activity, trace the wire toward the next module.
- If intermittent, perform wiggle tests along the harness and at connectors while monitoring the bus for failures to help locate a break or intermittent connector.
- Disconnect any recently added aftermarket modules or accessories and retest the network.
- If wiring checks good and bus activity still absent, consult manufacturer procedures for programming/flash requirements; reprogram or replace VCM only after confirming wiring and bus integrity.
- After repairs, clear codes, verify communication is restored, and perform functional tests and a road test to confirm the fault does not return.
Likely causes
- Disconnected or corroded VCM connector pins
- Blown fuse supplying the VCM or its serial bus interface
- Open or short in the Class 2 data wire between VCM and gateway/module
- Failed VCM or improper programming after replacement
- Aftermarket alarm, radio, or towing module pulling down the bus
Fault status
Status
Loss of Class 2 communication with Vehicle Control Module (VCM) — VCM not responding or Class 2 data bus signal absent/corrupted.
Repair difficulty: Medium
Diagnostic time: 1.0-3.5 hours
Similar codes
Repair manuals
Manual library for HUMMER
138
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Code
U1016
Other
U — Network/User
SCP (J1850) Invalid or Missing Data for Primary Id
AI status
Completed
Completed
100%
Causes
- Blown fuse or loss of VCM power/ignition feed
- Poor or missing ground at the VCM or common chassis ground
- Open, shorted or corroded Class 2 network wiring or connector(s)
- Corroded/damaged VCM connector pins or water intrusion
- Failed VCM/module or internal module fault
- Aftermarket accessory or module interfering with the Class 2 bus
Symptoms
- Scan tool shows "No Communication" or cannot connect to VCM
- Multiple unrelated DTCs or a network-related DTC set
- Malfunctioning or disabled vehicle systems that rely on the VCM
- Instrument cluster warnings or ignition/starter interlocks
- Intermittent operation of features (cruise, transmission shifts, etc.)
What to check
- Confirm U1016 present and check Freeze Frame/related DTCs and timestamps
- Verify battery voltage is within specification (key on and cranking)
- Check fuses and power circuits for VCM and related modules
- Visually inspect VCM connector and Class 2 wiring for damage, corrosion, or water entry
- Attempt to communicate with other modules on the Class 2 bus to determine scope of loss
- Disconnect aftermarket accessories that tie into the data bus and retest
Signal parameters
- Class 2 network: expect serial data activity on the data wire when ignition ON — absence indicates open/short
- Idle/steady voltage level and pulse transitions should be present; check with a scope or manufacturer-approved bus monitor
- Compare waveform or activity count to a known-good vehicle or factory specification using a lab scope/scan tool
- Observe for noise, missing frames, long pauses, or stuck-high/low conditions on the bus
Diagnostic algorithm
- Record all stored codes and freeze frame data. Note when the DTC sets and any relationship to vehicle symptoms.
- Attempt normal communications with the VCM using a factory scan tool. Confirm "no response" or intermittent response.
- Verify battery voltage (12.4–12.8 V nominal with engine off; >13 V when running). Repair battery/charging issues first.
- Inspect and test fuses and power feeds to the VCM; restore any blown/missing circuits and retest communication.
- Visually inspect the VCM connector and harness for corrosion, bent pins, water intrusion or physical damage; repair as needed.
- Backprobe the Class 2 data wire at the VCM connector and check for data activity with a scope or data bus monitor while key is ON. If no activity, trace the wire toward the next module.
- If intermittent, perform wiggle tests along the harness and at connectors while monitoring the bus for failures to help locate a break or intermittent connector.
- Disconnect any recently added aftermarket modules or accessories and retest the network.
- If wiring checks good and bus activity still absent, consult manufacturer procedures for programming/flash requirements; reprogram or replace VCM only after confirming wiring and bus integrity.
- After repairs, clear codes, verify communication is restored, and perform functional tests and a road test to confirm the fault does not return.
Likely causes
- Disconnected or corroded VCM connector pins
- Blown fuse supplying the VCM or its serial bus interface
- Open or short in the Class 2 data wire between VCM and gateway/module
- Failed VCM or improper programming after replacement
- Aftermarket alarm, radio, or towing module pulling down the bus
Fault status
Status
Loss of Class 2 communication with Vehicle Control Module (VCM) — VCM not responding or Class 2 data bus signal absent/corrupted.
Repair difficulty: Medium
Diagnostic time: 1.0-3.5 hours
Similar codes
Repair manuals
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