Code
B1440
HUMMER
B — Body
Power Mode Master Input Circuits Mismatch
AI status
Completed
Completed
100%
Causes
- Damaged or shorted wiring harness between ignition/power mode switch and vehicle modules
- Poor or intermittent connector contact (corrosion, bent pins, loose terminals)
- Faulty ignition switch / power mode selector (mechanical or electrical failure)
- Faulty body control module (BCM) or instrument cluster reporting power mode
- Low battery voltage or intermittent battery/ground connection
- Software/configuration mismatch or module needing reflash
Symptoms
- Malfunction of key-on/accessory functions (radio, windows, HVAC)
- No-crank or intermittent crank/no-start related to power mode
- Illumination of dash warning lamp(s) and stored B1440
- Unresponsive or inconsistent ignition key positions (ACC/RUN/START)
- Erratic accessory behavior or modules reverting to default/safe mode
What to check
- Scan for B1440 and any stored/related codes (U-codes, B-codes, P-codes)
- Verify battery voltage is healthy (12.4–12.8 V at rest, >13.5 V with engine running)
- Inspect connectors and wiring at the ignition/power mode switch, BCM, and IPC
- Backprobe power mode signal circuits and monitor while cycling key positions
- Check for CAN/LIN errors or modules reporting lost communication
- Perform wiggle test on harness while monitoring signal and code status
Signal parameters
- Power mode signal expected states: OFF, ACC, RUN (IGN), START — verify correct state transitions when key operated
- Voltage on power mode feed: near battery voltage (~12 V) when asserted, ~0 V when not; some inputs are low-side switched or pull-ups — consult wiring diagram
- Digital/logic inputs may be switched to ground or to ignition voltage; open circuits or intermediate voltages indicate wiring/connector issues
- CAN/LIN bus messages: modules should publish consistent power mode status; check for missing or conflicting messages
Diagnostic algorithm
- Retrieve all DTCs and freeze frame data. Note any communication (U0xxx) or voltage (P0562) codes.
- Verify battery condition and charge if needed. Clear codes and attempt to reproduce with a fully charged battery.
- Visually inspect connectors and wiring for damage, corrosion, or pin distortion at ignition switch, BCM, and instrument cluster.
- Backprobe the power mode input circuits at the switch and at the receiving module(s). With a DVOM or scope, observe signal behavior across OFF/ACC/RUN/START. Look for missing transitions, intermittent, or contradictory states between modules.
- If signals are incorrect at the module but correct at the switch, trace and repair wiring/connectors between switch and module. If signals are incorrect at the switch, test/replace the ignition/power mode switch.
- Monitor CAN/LIN communications with a scan tool to ensure modules are broadcasting and receiving power mode messages consistently. Repair bus faults (terminations, shorts) if present.
- If wiring and switch check good and communication is stable, check for module software updates or configuration errors. Reflash or reprogram BCM/IPC as per manufacturer service information.
- Replace the affected module only after confirming a hardware failure; verify repair by clearing codes and performing a full function test across multiple key cycles.
Likely causes
- Loose or corroded connector at ignition switch or BCM
- Open or shorted signal wire between ignition switch and BCM/IPC
- Faulty ignition switch that fails to assert expected voltage in a key position
- Module communication failure (BCM or cluster) or lost CAN messages
Fault status
Status
Power Mode Master input circuits report inconsistent or invalid states between modules; vehicle modules disagree on ignition/power mode.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Repair manuals
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138
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