Code
B1520
ALFA ROMEO
B — Body
Bonnet switch circuit
Views:
UK: 5
EN: 13
RU: 6
AI status
Completed
Completed
100%
Causes
- Broken or shorted wiring in bonnet switch circuit
- Corroded or disconnected connector at bonnet switch or BCM
- Faulty bonnet/hood latch switch
- Blown or intermittent fuse or fusible link powering the circuit
- Poor ground connection
- Faulty BCM or related control module
Symptoms
- Vehicle may indicate bonnet open/warning lamp illuminated
- Interior dome light or alarm may stay on or not behave correctly
- Central locking or alarm false triggers or refuses to arm
- Impaired automatic safety/interlock features tied to bonnet status
- Stored B1520 fault and possibly related communications messages
What to check
- Visually inspect bonnet latch/switch, wiring harness, and protective boots for damage or corrosion
- Scan vehicle with a capable diagnostic tool: read freeze frame, live data, and any related codes
- Check relevant fuses/power supplies for the body control module and bonnet circuit
- Wiggle test wiring while observing live data to reproduce the fault
- Measure continuity and resistance of switch circuit with switch operated
- Measure signal voltage to BCM with ignition on (and per service manual states)
Signal parameters
- Switch closed: near 0 ohms (continuity) between switch terminals or switch terminal to ground depending on design
- Switch open: very high resistance (typically >1 MΩ) / open circuit
- Voltage at BCM input: either pulled to battery voltage (~11–14 V) when open and near 0 V when closed, or logic-level (0 V/5 V) depending on module design — consult factory wiring
- No switching chatter on the signal when actuating the bonnet (stable open/closed states)
Diagnostic algorithm
- Safety first: Park on level ground, apply parking brake, switch off ignition. Follow manufacturer procedures for working near the engine and electrical system.
- Use a scan tool: read and record all stored codes and freeze frame data. Note when B1520 is set (ignition state, vehicle motion, recent events). Clear codes and see if B1520 returns.
- Visual inspection: open bonnet and inspect latch, switch, connector, and wiring harness along the bonnet and hinge areas for damage, corrosion, or water intrusion.
- Check fuses and power: verify related fuses and any supply to the bonnet switch circuit and BCM are present and not intermittent.
- Backprobe the switch connector: with ignition on, monitor live signal to BCM while operating the bonnet switch. Confirm the signal changes state when the switch is actuated.
- Continuity test: with battery isolated if required, disconnect the connector and measure continuity/resistance across switch terminals. Expect near 0 Ω when closed and open/infinite when open. If the switch does not meet these values, replace switch.
- Wiggle and flex test wiring: with multimeter or scope monitoring the signal, flex wiring around hinge and boot to reproduce intermittent faults. Repair damaged sections and secure harness.
- Check grounds: measure voltage drops and inspect ground points for corrosion/tightness. Clean/tighten as needed.
- Isolate BCM input: if wiring and switch are good, check for short to 12 V or ground between the switch wire and supply/ground. If wiring checks out, suspect BCM/input circuit fault and test/replace per service procedures.
- After repairs: clear codes, perform functional tests (open/close bonnet, arm alarm if relevant) and road/idle test to confirm fault does not return.
Likely causes
- Connector at bonnet switch corroded or loose
- Wiring damaged at hood hinge or protector boot (flex point)
- Bonnet switch contacts stuck or contaminated
- Open circuit to BCM input or short to ground/12V
- Intermittent failure after water exposure or accident damage
Fault status
Status
Bonnet switch circuit malfunction detected. Signal to body control module out of specification (open, short, or intermittent).
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
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Code
B1520
FIAT
B — Body
Bonnet switch circuit
Views:
UK: 4
EN: 11
RU: 6
AI status
Completed
Completed
100%
Causes
- Broken or shorted wiring in bonnet switch circuit
- Corroded or disconnected connector at bonnet switch or BCM
- Faulty bonnet/hood latch switch
- Blown or intermittent fuse or fusible link powering the circuit
- Poor ground connection
- Faulty BCM or related control module
Symptoms
- Vehicle may indicate bonnet open/warning lamp illuminated
- Interior dome light or alarm may stay on or not behave correctly
- Central locking or alarm false triggers or refuses to arm
- Impaired automatic safety/interlock features tied to bonnet status
- Stored B1520 fault and possibly related communications messages
What to check
- Visually inspect bonnet latch/switch, wiring harness, and protective boots for damage or corrosion
- Scan vehicle with a capable diagnostic tool: read freeze frame, live data, and any related codes
- Check relevant fuses/power supplies for the body control module and bonnet circuit
- Wiggle test wiring while observing live data to reproduce the fault
- Measure continuity and resistance of switch circuit with switch operated
- Measure signal voltage to BCM with ignition on (and per service manual states)
Signal parameters
- Switch closed: near 0 ohms (continuity) between switch terminals or switch terminal to ground depending on design
- Switch open: very high resistance (typically >1 MΩ) / open circuit
- Voltage at BCM input: either pulled to battery voltage (~11–14 V) when open and near 0 V when closed, or logic-level (0 V/5 V) depending on module design — consult factory wiring
- No switching chatter on the signal when actuating the bonnet (stable open/closed states)
Diagnostic algorithm
- Safety first: Park on level ground, apply parking brake, switch off ignition. Follow manufacturer procedures for working near the engine and electrical system.
- Use a scan tool: read and record all stored codes and freeze frame data. Note when B1520 is set (ignition state, vehicle motion, recent events). Clear codes and see if B1520 returns.
- Visual inspection: open bonnet and inspect latch, switch, connector, and wiring harness along the bonnet and hinge areas for damage, corrosion, or water intrusion.
- Check fuses and power: verify related fuses and any supply to the bonnet switch circuit and BCM are present and not intermittent.
- Backprobe the switch connector: with ignition on, monitor live signal to BCM while operating the bonnet switch. Confirm the signal changes state when the switch is actuated.
- Continuity test: with battery isolated if required, disconnect the connector and measure continuity/resistance across switch terminals. Expect near 0 Ω when closed and open/infinite when open. If the switch does not meet these values, replace switch.
- Wiggle and flex test wiring: with multimeter or scope monitoring the signal, flex wiring around hinge and boot to reproduce intermittent faults. Repair damaged sections and secure harness.
- Check grounds: measure voltage drops and inspect ground points for corrosion/tightness. Clean/tighten as needed.
- Isolate BCM input: if wiring and switch are good, check for short to 12 V or ground between the switch wire and supply/ground. If wiring checks out, suspect BCM/input circuit fault and test/replace per service procedures.
- After repairs: clear codes, perform functional tests (open/close bonnet, arm alarm if relevant) and road/idle test to confirm fault does not return.
Likely causes
- Connector at bonnet switch corroded or loose
- Wiring damaged at hood hinge or protector boot (flex point)
- Bonnet switch contacts stuck or contaminated
- Open circuit to BCM input or short to ground/12V
- Intermittent failure after water exposure or accident damage
Fault status
Status
Bonnet switch circuit malfunction detected. Signal to body control module out of specification (open, short, or intermittent).
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
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Code
B1520
MITSUBISHI
B — Body
DR.buckle SW fault
Views:
UK: 11
EN: 21
RU: 24
AI status
Completed
Completed
100%
Causes
- Broken or shorted wiring in bonnet switch circuit
- Corroded or disconnected connector at bonnet switch or BCM
- Faulty bonnet/hood latch switch
- Blown or intermittent fuse or fusible link powering the circuit
- Poor ground connection
- Faulty BCM or related control module
Symptoms
- Vehicle may indicate bonnet open/warning lamp illuminated
- Interior dome light or alarm may stay on or not behave correctly
- Central locking or alarm false triggers or refuses to arm
- Impaired automatic safety/interlock features tied to bonnet status
- Stored B1520 fault and possibly related communications messages
What to check
- Visually inspect bonnet latch/switch, wiring harness, and protective boots for damage or corrosion
- Scan vehicle with a capable diagnostic tool: read freeze frame, live data, and any related codes
- Check relevant fuses/power supplies for the body control module and bonnet circuit
- Wiggle test wiring while observing live data to reproduce the fault
- Measure continuity and resistance of switch circuit with switch operated
- Measure signal voltage to BCM with ignition on (and per service manual states)
Signal parameters
- Switch closed: near 0 ohms (continuity) between switch terminals or switch terminal to ground depending on design
- Switch open: very high resistance (typically >1 MΩ) / open circuit
- Voltage at BCM input: either pulled to battery voltage (~11–14 V) when open and near 0 V when closed, or logic-level (0 V/5 V) depending on module design — consult factory wiring
- No switching chatter on the signal when actuating the bonnet (stable open/closed states)
Diagnostic algorithm
- Safety first: Park on level ground, apply parking brake, switch off ignition. Follow manufacturer procedures for working near the engine and electrical system.
- Use a scan tool: read and record all stored codes and freeze frame data. Note when B1520 is set (ignition state, vehicle motion, recent events). Clear codes and see if B1520 returns.
- Visual inspection: open bonnet and inspect latch, switch, connector, and wiring harness along the bonnet and hinge areas for damage, corrosion, or water intrusion.
- Check fuses and power: verify related fuses and any supply to the bonnet switch circuit and BCM are present and not intermittent.
- Backprobe the switch connector: with ignition on, monitor live signal to BCM while operating the bonnet switch. Confirm the signal changes state when the switch is actuated.
- Continuity test: with battery isolated if required, disconnect the connector and measure continuity/resistance across switch terminals. Expect near 0 Ω when closed and open/infinite when open. If the switch does not meet these values, replace switch.
- Wiggle and flex test wiring: with multimeter or scope monitoring the signal, flex wiring around hinge and boot to reproduce intermittent faults. Repair damaged sections and secure harness.
- Check grounds: measure voltage drops and inspect ground points for corrosion/tightness. Clean/tighten as needed.
- Isolate BCM input: if wiring and switch are good, check for short to 12 V or ground between the switch wire and supply/ground. If wiring checks out, suspect BCM/input circuit fault and test/replace per service procedures.
- After repairs: clear codes, perform functional tests (open/close bonnet, arm alarm if relevant) and road/idle test to confirm fault does not return.
Likely causes
- Connector at bonnet switch corroded or loose
- Wiring damaged at hood hinge or protector boot (flex point)
- Bonnet switch contacts stuck or contaminated
- Open circuit to BCM input or short to ground/12V
- Intermittent failure after water exposure or accident damage
Fault status
Status
Bonnet switch circuit malfunction detected. Signal to body control module out of specification (open, short, or intermittent).
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
Similar codes
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Send to email
Code
B1520
Other
B — Body
Hood Switch Circuit Open
Views:
UK: 23
EN: 43
RU: 43
AI status
Completed
Completed
100%
Causes
- Broken or shorted wiring in bonnet switch circuit
- Corroded or disconnected connector at bonnet switch or BCM
- Faulty bonnet/hood latch switch
- Blown or intermittent fuse or fusible link powering the circuit
- Poor ground connection
- Faulty BCM or related control module
Symptoms
- Vehicle may indicate bonnet open/warning lamp illuminated
- Interior dome light or alarm may stay on or not behave correctly
- Central locking or alarm false triggers or refuses to arm
- Impaired automatic safety/interlock features tied to bonnet status
- Stored B1520 fault and possibly related communications messages
What to check
- Visually inspect bonnet latch/switch, wiring harness, and protective boots for damage or corrosion
- Scan vehicle with a capable diagnostic tool: read freeze frame, live data, and any related codes
- Check relevant fuses/power supplies for the body control module and bonnet circuit
- Wiggle test wiring while observing live data to reproduce the fault
- Measure continuity and resistance of switch circuit with switch operated
- Measure signal voltage to BCM with ignition on (and per service manual states)
Signal parameters
- Switch closed: near 0 ohms (continuity) between switch terminals or switch terminal to ground depending on design
- Switch open: very high resistance (typically >1 MΩ) / open circuit
- Voltage at BCM input: either pulled to battery voltage (~11–14 V) when open and near 0 V when closed, or logic-level (0 V/5 V) depending on module design — consult factory wiring
- No switching chatter on the signal when actuating the bonnet (stable open/closed states)
Diagnostic algorithm
- Safety first: Park on level ground, apply parking brake, switch off ignition. Follow manufacturer procedures for working near the engine and electrical system.
- Use a scan tool: read and record all stored codes and freeze frame data. Note when B1520 is set (ignition state, vehicle motion, recent events). Clear codes and see if B1520 returns.
- Visual inspection: open bonnet and inspect latch, switch, connector, and wiring harness along the bonnet and hinge areas for damage, corrosion, or water intrusion.
- Check fuses and power: verify related fuses and any supply to the bonnet switch circuit and BCM are present and not intermittent.
- Backprobe the switch connector: with ignition on, monitor live signal to BCM while operating the bonnet switch. Confirm the signal changes state when the switch is actuated.
- Continuity test: with battery isolated if required, disconnect the connector and measure continuity/resistance across switch terminals. Expect near 0 Ω when closed and open/infinite when open. If the switch does not meet these values, replace switch.
- Wiggle and flex test wiring: with multimeter or scope monitoring the signal, flex wiring around hinge and boot to reproduce intermittent faults. Repair damaged sections and secure harness.
- Check grounds: measure voltage drops and inspect ground points for corrosion/tightness. Clean/tighten as needed.
- Isolate BCM input: if wiring and switch are good, check for short to 12 V or ground between the switch wire and supply/ground. If wiring checks out, suspect BCM/input circuit fault and test/replace per service procedures.
- After repairs: clear codes, perform functional tests (open/close bonnet, arm alarm if relevant) and road/idle test to confirm fault does not return.
Likely causes
- Connector at bonnet switch corroded or loose
- Wiring damaged at hood hinge or protector boot (flex point)
- Bonnet switch contacts stuck or contaminated
- Open circuit to BCM input or short to ground/12V
- Intermittent failure after water exposure or accident damage
Fault status
Status
Bonnet switch circuit malfunction detected. Signal to body control module out of specification (open, short, or intermittent).
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
Similar codes
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Was this AI description helpful?
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