Code
B1522
ALFA ROMEO
B — Body
Bonnet switch circuit
AI status
Completed
Completed
100%
Causes
- Open or short in bonnet switch wiring
- Corroded or damaged bonnet (hood) switch
- Poor connector contacts or water ingress at switch or module connector
- Faulty body control module (BCM) or instrument cluster input
- Intermittent mechanical switch contact (sticking)
- Blown fuse or poor ground related to the bonnet circuit
Symptoms
- Bonnet/hood open warning lamp or message on dash
- Alarm or immobilizer may not arm/disarm correctly
- Interior courtesy lights may stay on or not come on as expected
- Central locking or security system behaves intermittently
- DTC stored and possibly multiple attempts to set/clear the message
What to check
- Read stored DTCs and freeze frame data with a diagnostic scanner; note related codes
- Visually inspect bonnet switch, wiring along hinge, and connectors for damage or corrosion
- Wiggle harness while watching live data to reproduce intermittent faults
- Backprobe the switch connector and check voltage/ground with bonnet open/closed
- Check continuity and resistance of switch with multimeter (switch open = high/infinite, closed = near 0 Ω)
- Check power and ground fuses and module grounds related to body control module
Signal parameters
- Typical switch behavior: open-circuit when bonnet closed, closed to ground when bonnet open (or vice versa depending on vehicle)
- Idle voltage at signal line with switch open: near battery voltage (approx. 12 V) or pull-up voltage specified by module
- Voltage at signal line with switch closed: near 0 V (ground) or low logic level
- Closed-switch resistance: ≈ 0–5 Ω (near short to ground)
- Open-switch resistance: very high / infinite
Diagnostic algorithm
- Confirm the B1522 code and any related codes with a diagnostic scanner. Record freeze frame/live data for bonnet switch input.
- Visually inspect bonnet switch, striker area, wiring along the hinge, and both connectors for damage, dirt, corrosion, or signs of water ingress.
- With connector disconnected, measure resistance across the switch while operating the bonnet latch: closed = open circuit (high Ω) or closed = low Ω depending on switch design; compare to expected behavior.
- Reconnect and backprobe the signal wire. Observe voltage with bonnet closed and open. Expect a clear change (e.g., ~12 V ↔ ~0 V). If no change, move to wiring checks.
- Check continuity between the switch signal pin and the BCM/input pin. Repair any open circuits or chafing found, especially at hinge points.
- Check for shorts to battery or ground by measuring resistance from the signal wire to battery + and to chassis ground with connector disconnected.
- Clean or replace corroded connectors. If wiring and switch test OK but signal remains incorrect, check BCM power/ground and inputs. Swap or test BCM input if procedures available.
- After repairs, clear codes and perform functional test by opening/closing bonnet and verifying the input changes in live data and that the DTC does not return.
- If intermittent: monitor with scanner over time or perform wiggle test to replicate intermittent failure; secure or replace wiring as required.
Likely causes
- Broken or chafed harness where it flexes at the bonnet hinge
- Corrosion inside the bonnet switch assembly (common in wet climates)
- Connector pin pushed out, bent, or contaminated at the switch or BCM
- Short to battery or chassis ground caused by damaged insulation
- Internal failure of the bonnet switch contacts
Fault status
Status
Bonnet switch circuit fault — abnormal/open/short/intermittent signal detected by body control module. May affect bonnet open warning, alarm and interior lighting functions.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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