Code
B1860
HUMMER
B — Body
Driver Lumbar Vert Sensor Circuit Malfunction
AI status
Completed
Completed
100%
Causes
- Broken or chafed wiring in the seat harness
- Loose, corroded, or poorly seated connector(s) at the lumbar sensor or seat control module
- Failed lumbar position sensor (potentiometer/position transducer)
- Short to battery or ground on the signal/reference wire
- Faulty seat control module (rare)
- Water intrusion or contamination in seat (causes corrosion/intermittent faults)
Symptoms
- Driver lumbar does not move or adjust vertically
- Lumbar adjusts erratically or returns incorrect position
- DTC stored in body/seat module and may illuminate a service message
- Other seat comfort functions (memory, adjustments) may be affected or inoperative
What to check
- Retrieve DTC and freeze frame data with a scan tool; record related seat/comfort codes
- Visually inspect the driver seat and underside for water damage, corrosion, or physical damage
- Inspect connectors at the lumbar sensor, seat wiring harness, and seat control module for bent pins, corrosion, or loose mates
- Perform a wiggle test: operate lumbar while moving wiring and connectors to try to reproduce fault or change behavior
- Follow service manual SRS precautions before working on seat wiring (disconnect battery and wait required time)
- Consult wiring diagram/service manual to identify sensor pinout, reference voltage, signal, and ground pins
Signal parameters
- Most lumbar position sensors are 3‑wire (5 V reference, signal, ground). Expected reference: ≈5 V (typically 4.5–5.5 V) with ignition/key on.
- Signal voltage typically varies with position: about 0.5–4.5 V across travel (exact range depends on sensor design).
- Ground should be near 0 V with low resistance to chassis ground.
- If sensor is a variable resistor, resistance across signal and ground will vary smoothly (often in the kiloohm range) as the lumbar moves.
Diagnostic algorithm
- Safety first: disable battery/power per service manual before disconnecting seat connectors or performing repairs around SRS components.
- Step 1 — Scan and document: Connect a scan tool, read B1860 and any related codes, record freeze frame and live data for lumbar position if available.
- Step 2 — Visual inspection: Check seat upholstery, seams, and underside for water intrusion, foreign objects, or damaged components. Inspect connector bodies and pins for corrosion, bent pins, or contamination.
- Step 3 — Identify wiring: Use the factory wiring diagram to locate the lumbar sensor wires and pin assignments at the sensor and seat control module.
- Step 4 — Backprobe and measure: With ignition on (and vehicle in a safe state), backprobe the harness at the sensor or connector. Verify reference voltage (≈5 V), ground continuity, and signal voltage while moving the lumbar. Signal should change smoothly with movement.
- Step 5 — Continuity and short test: With ignition off and battery disconnected, check continuity of the signal and ground wires from the sensor connector back to the seat module. Check for shorts to battery or chassis ground.
- Step 6 — Wiggle test: With harness connected and ignition on, operate lumbar while gently flexing the wiring and connectors to check for intermittent faults.
- Step 7 — Swap/replace sensor: If harness and supply are good and signal is abnormal or non‑variable, replace the lumbar position sensor. If replacement sensor shows same issue, suspect seat control module.
- Step 8 — Module check: If wiring and sensor are confirmed good, test/replace the seat control module per factory procedures. After repairs, clear codes and verify proper operation and that code does not return.
- Note: Follow manufacturer's service manual for pinouts, test voltages, resistance specs, and SRS/airbag safety procedures.
Likely causes
- Open or intermittent wiring between lumbar sensor and seat module
- Failed lumbar position sensor (worn potentiometer)
- Corroded/poor connector at sensor or module
- Short to ground on signal or reference circuit
Fault status
Status
Seat control module has detected an open, short, intermittent, or out‑of‑range signal from the driver vertical lumbar position sensor circuit.
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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