Code
B2878
HUMMER
B — Body
Tilt Down Switch Circuit Malfunction
AI status
Completed
Completed
100%
Causes
- Failed or worn tilt-down switch
- Open, short to ground, or short to voltage in the switch wiring
- Corroded or loose connector at the switch or BCM
- Blown fuse or intermittent power/ground supply
- Water intrusion or physical damage to harness or switch
- Faulty body control module (BCM) or related control module
Symptoms
- Tilt-down function does not operate when switch is pressed
- Intermittent operation of tilt-down feature
- Stored B2878 DTC and possibly related body electrical codes
- No response from switch or unexpected behavior of tilt mechanism
- Possible blown fuse for the circuit
What to check
- Scan the vehicle and record B2878 plus any related DTCs and freeze-frame data
- Verify battery voltage is stable (9–14 V) and inspect relevant fuses
- Operate the tilt-down switch while observing scanner data or module inputs
- Visually inspect switch, connector, and wiring for damage, corrosion, or water
- Wiggle the wiring harness and connector while watching for changes or freeze-frame updates
- Check ground connections and power feed to the switch
Signal parameters
- Reference/power feed to switch: nominal battery voltage (~9–14 V) when key on
- Switch output: should show continuity (low resistance) to the expected return when actuated
- Open switch: high resistance/OL; closed switch: near 0 Ω to the return
- Module input signal toggles when switch is pressed (voltage typically near 0 V or battery voltage depending on design)
- No module input change or stuck voltage indicates wiring/switch fault
Diagnostic algorithm
- Retrieve and record freeze-frame data and any additional DTCs. Confirm B2878 is current or intermittent.
- Inspect fuse(s) and relays related to the tilt/comfort system. Replace any blown fuses and retest.
- Visually inspect the tilt-down switch, bezel, and harness for damage, moisture, or corrosion. Repair as needed.
- With a DVOM or scope, backprobe the switch connector and verify reference power and ground presence with key on.
- Operate the switch while measuring the switch signal line to the BCM. Confirm the signal changes as expected (continuity or voltage toggle).
- If no signal change, check continuity between switch and module connector; repair any open or shorted wiring.
- Repair corroded connectors or poor pin contacts. After repairs, clear codes and re-test function and road-test if applicable.
- If wiring and switch test good but code returns, perform module input/output tests per factory manual. Consider BCM repair or replacement as last resort.
Likely causes
- Failed tilt-down switch (most common)
- Damaged wiring or broken/shorted conductor between switch and module
- Connector corrosion or poor pin contact at the switch or module
- Intermittent power/ground (fuse, splice, or ground strap issue)
- Less likely: BCM internal fault
Fault status
Status
B2878 - Tilt Down Switch Circuit Malfunction. Inspect switch, wiring, power/ground, and related fuses/connectors. Clear code after repair and verify operation.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Repair manuals
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138
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