Code
B1347
ALFA ROMEO
B — Body
Heated rear window resistance input relay coil
Views:
UK: 3
EN: 1
RU: 3
AI status
Completed
Completed
100%
Causes
- Defective relay coil (stuck open or shorted)
- Blown fuse supplying the relay
- Open or shorted wiring to the relay coil (broken wire, chafing)
- Poor or corroded connector or terminal at the relay
- Bad ground or inadequate power supply to the relay coil
- Fault in the Body Control Module (BCM) / relay driver circuit
Symptoms
- Heated rear window (rear defogger) does not operate
- No audible click from the relay when defogger is commanded
- Rear defogger indicator lamp may not illuminate or may behave intermittently
- Possible blown fuse repeated after replacement
- DTC B1347 stored in body control module
What to check
- Scan and record freeze frame and related codes; clear codes and attempt to reproduce
- Visual inspection of relay, connector, wiring harness, and fuse for damage or corrosion
- Verify presence of correct fuse(s) and replace if blown (note if it blows again)
- Check for proper connector fit and signs of water ingress at relay socket
- Measure coil resistance with relay removed from socket
- Check for 12 V supply to the relay power terminal when ignition is ON
Signal parameters
- Relay coil resistance (typical): approximately 20–150 ohms (manufacturer specification required for exact value)
- Activation/control voltage: approx. 11–14 V present at coil when defogger is commanded
- Coil current draw: typically tens to a few hundred milliamps (varies by relay)
- When energized, relay supply output to rear window heater should be near battery voltage
- No control voltage (0 V) at coil indicates BCM/driver not commanding the relay
Diagnostic algorithm
- Retrieve all stored codes and freeze frame data. Note any related body or powertrain codes.
- Perform a visual inspection of the rear window relay, socket, harness, and fuses for signs of damage, corrosion, or melted plastic.
- Verify the relevant fuse(s) for the defogger are intact. Replace fuse if blown and observe whether it blows again when system is activated.
- Remove the relay and measure coil resistance across the coil terminals with an ohmmeter. Compare to typical range; an open or shorted coil indicates a faulty relay.
- With the relay removed, check that the relay socket has battery positive at the supply terminal with ignition ON and that the ground/return is good.
- Command the defogger ON and measure the control/driver voltage from the BCM at the relay coil input terminal. A switching voltage (near battery) should appear when commanded.
- If control voltage is present but relay coil is open/short, replace the relay and retest. If control voltage is absent, trace wiring back to the BCM: check continuity, inspect for shorts to ground/battery.
- Perform a wiggle and moisture test on connectors and harness while commanding system to reproduce intermittent faults.
- If wiring and relay check OK but fault persists, test/scan the BCM outputs and consider BCM replacement or reprogramming per manufacturer procedures.
- After repairs, clear codes and verify correct operation of the heated rear window and that DTC B1347 does not return.
Likely causes
- Corroded/loose relay connector or terminals
- Failed relay coil
- Blown or partially blown fuse in defogger circuit
- Open or short in wiring between relay and BCM
- Faulty BCM output (less common)
Fault status
Status
Heated rear window resistance input relay coil fault (open/short/intermittent). Check relay, fuse, connector, wiring and BCM output before replacing control module.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
B1347
FIAT
B — Body
Heated rear window resistance input relay coil
Views:
UK: 1
EN: 1
RU: 2
AI status
Completed
Completed
100%
Causes
- Defective relay coil (stuck open or shorted)
- Blown fuse supplying the relay
- Open or shorted wiring to the relay coil (broken wire, chafing)
- Poor or corroded connector or terminal at the relay
- Bad ground or inadequate power supply to the relay coil
- Fault in the Body Control Module (BCM) / relay driver circuit
Symptoms
- Heated rear window (rear defogger) does not operate
- No audible click from the relay when defogger is commanded
- Rear defogger indicator lamp may not illuminate or may behave intermittently
- Possible blown fuse repeated after replacement
- DTC B1347 stored in body control module
What to check
- Scan and record freeze frame and related codes; clear codes and attempt to reproduce
- Visual inspection of relay, connector, wiring harness, and fuse for damage or corrosion
- Verify presence of correct fuse(s) and replace if blown (note if it blows again)
- Check for proper connector fit and signs of water ingress at relay socket
- Measure coil resistance with relay removed from socket
- Check for 12 V supply to the relay power terminal when ignition is ON
Signal parameters
- Relay coil resistance (typical): approximately 20–150 ohms (manufacturer specification required for exact value)
- Activation/control voltage: approx. 11–14 V present at coil when defogger is commanded
- Coil current draw: typically tens to a few hundred milliamps (varies by relay)
- When energized, relay supply output to rear window heater should be near battery voltage
- No control voltage (0 V) at coil indicates BCM/driver not commanding the relay
Diagnostic algorithm
- Retrieve all stored codes and freeze frame data. Note any related body or powertrain codes.
- Perform a visual inspection of the rear window relay, socket, harness, and fuses for signs of damage, corrosion, or melted plastic.
- Verify the relevant fuse(s) for the defogger are intact. Replace fuse if blown and observe whether it blows again when system is activated.
- Remove the relay and measure coil resistance across the coil terminals with an ohmmeter. Compare to typical range; an open or shorted coil indicates a faulty relay.
- With the relay removed, check that the relay socket has battery positive at the supply terminal with ignition ON and that the ground/return is good.
- Command the defogger ON and measure the control/driver voltage from the BCM at the relay coil input terminal. A switching voltage (near battery) should appear when commanded.
- If control voltage is present but relay coil is open/short, replace the relay and retest. If control voltage is absent, trace wiring back to the BCM: check continuity, inspect for shorts to ground/battery.
- Perform a wiggle and moisture test on connectors and harness while commanding system to reproduce intermittent faults.
- If wiring and relay check OK but fault persists, test/scan the BCM outputs and consider BCM replacement or reprogramming per manufacturer procedures.
- After repairs, clear codes and verify correct operation of the heated rear window and that DTC B1347 does not return.
Likely causes
- Corroded/loose relay connector or terminals
- Failed relay coil
- Blown or partially blown fuse in defogger circuit
- Open or short in wiring between relay and BCM
- Faulty BCM output (less common)
Fault status
Status
Heated rear window resistance input relay coil fault (open/short/intermittent). Check relay, fuse, connector, wiring and BCM output before replacing control module.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
B1347
HUMMER
B — Body
Very Low A/C Refrigerant Warning
Views:
UK: 2
EN: 4
RU: 5
AI status
Completed
Completed
100%
Causes
- Defective relay coil (stuck open or shorted)
- Blown fuse supplying the relay
- Open or shorted wiring to the relay coil (broken wire, chafing)
- Poor or corroded connector or terminal at the relay
- Bad ground or inadequate power supply to the relay coil
- Fault in the Body Control Module (BCM) / relay driver circuit
Symptoms
- Heated rear window (rear defogger) does not operate
- No audible click from the relay when defogger is commanded
- Rear defogger indicator lamp may not illuminate or may behave intermittently
- Possible blown fuse repeated after replacement
- DTC B1347 stored in body control module
What to check
- Scan and record freeze frame and related codes; clear codes and attempt to reproduce
- Visual inspection of relay, connector, wiring harness, and fuse for damage or corrosion
- Verify presence of correct fuse(s) and replace if blown (note if it blows again)
- Check for proper connector fit and signs of water ingress at relay socket
- Measure coil resistance with relay removed from socket
- Check for 12 V supply to the relay power terminal when ignition is ON
Signal parameters
- Relay coil resistance (typical): approximately 20–150 ohms (manufacturer specification required for exact value)
- Activation/control voltage: approx. 11–14 V present at coil when defogger is commanded
- Coil current draw: typically tens to a few hundred milliamps (varies by relay)
- When energized, relay supply output to rear window heater should be near battery voltage
- No control voltage (0 V) at coil indicates BCM/driver not commanding the relay
Diagnostic algorithm
- Retrieve all stored codes and freeze frame data. Note any related body or powertrain codes.
- Perform a visual inspection of the rear window relay, socket, harness, and fuses for signs of damage, corrosion, or melted plastic.
- Verify the relevant fuse(s) for the defogger are intact. Replace fuse if blown and observe whether it blows again when system is activated.
- Remove the relay and measure coil resistance across the coil terminals with an ohmmeter. Compare to typical range; an open or shorted coil indicates a faulty relay.
- With the relay removed, check that the relay socket has battery positive at the supply terminal with ignition ON and that the ground/return is good.
- Command the defogger ON and measure the control/driver voltage from the BCM at the relay coil input terminal. A switching voltage (near battery) should appear when commanded.
- If control voltage is present but relay coil is open/short, replace the relay and retest. If control voltage is absent, trace wiring back to the BCM: check continuity, inspect for shorts to ground/battery.
- Perform a wiggle and moisture test on connectors and harness while commanding system to reproduce intermittent faults.
- If wiring and relay check OK but fault persists, test/scan the BCM outputs and consider BCM replacement or reprogramming per manufacturer procedures.
- After repairs, clear codes and verify correct operation of the heated rear window and that DTC B1347 does not return.
Likely causes
- Corroded/loose relay connector or terminals
- Failed relay coil
- Blown or partially blown fuse in defogger circuit
- Open or short in wiring between relay and BCM
- Faulty BCM output (less common)
Fault status
Status
Heated rear window resistance input relay coil fault (open/short/intermittent). Check relay, fuse, connector, wiring and BCM output before replacing control module.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Similar codes
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Code
B1347
Other
B — Body
Heated Backlite Relay Circuit Failure
Views:
UK: 11
EN: 22
RU: 18
AI status
Completed
Completed
100%
Causes
- Defective relay coil (stuck open or shorted)
- Blown fuse supplying the relay
- Open or shorted wiring to the relay coil (broken wire, chafing)
- Poor or corroded connector or terminal at the relay
- Bad ground or inadequate power supply to the relay coil
- Fault in the Body Control Module (BCM) / relay driver circuit
Symptoms
- Heated rear window (rear defogger) does not operate
- No audible click from the relay when defogger is commanded
- Rear defogger indicator lamp may not illuminate or may behave intermittently
- Possible blown fuse repeated after replacement
- DTC B1347 stored in body control module
What to check
- Scan and record freeze frame and related codes; clear codes and attempt to reproduce
- Visual inspection of relay, connector, wiring harness, and fuse for damage or corrosion
- Verify presence of correct fuse(s) and replace if blown (note if it blows again)
- Check for proper connector fit and signs of water ingress at relay socket
- Measure coil resistance with relay removed from socket
- Check for 12 V supply to the relay power terminal when ignition is ON
Signal parameters
- Relay coil resistance (typical): approximately 20–150 ohms (manufacturer specification required for exact value)
- Activation/control voltage: approx. 11–14 V present at coil when defogger is commanded
- Coil current draw: typically tens to a few hundred milliamps (varies by relay)
- When energized, relay supply output to rear window heater should be near battery voltage
- No control voltage (0 V) at coil indicates BCM/driver not commanding the relay
Diagnostic algorithm
- Retrieve all stored codes and freeze frame data. Note any related body or powertrain codes.
- Perform a visual inspection of the rear window relay, socket, harness, and fuses for signs of damage, corrosion, or melted plastic.
- Verify the relevant fuse(s) for the defogger are intact. Replace fuse if blown and observe whether it blows again when system is activated.
- Remove the relay and measure coil resistance across the coil terminals with an ohmmeter. Compare to typical range; an open or shorted coil indicates a faulty relay.
- With the relay removed, check that the relay socket has battery positive at the supply terminal with ignition ON and that the ground/return is good.
- Command the defogger ON and measure the control/driver voltage from the BCM at the relay coil input terminal. A switching voltage (near battery) should appear when commanded.
- If control voltage is present but relay coil is open/short, replace the relay and retest. If control voltage is absent, trace wiring back to the BCM: check continuity, inspect for shorts to ground/battery.
- Perform a wiggle and moisture test on connectors and harness while commanding system to reproduce intermittent faults.
- If wiring and relay check OK but fault persists, test/scan the BCM outputs and consider BCM replacement or reprogramming per manufacturer procedures.
- After repairs, clear codes and verify correct operation of the heated rear window and that DTC B1347 does not return.
Likely causes
- Corroded/loose relay connector or terminals
- Failed relay coil
- Blown or partially blown fuse in defogger circuit
- Open or short in wiring between relay and BCM
- Faulty BCM output (less common)
Fault status
Status
Heated rear window resistance input relay coil fault (open/short/intermittent). Check relay, fuse, connector, wiring and BCM output before replacing control module.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Similar codes
Workshop Manuals
Available brands with manuals
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Land Rover Defender Workshop Manual 1999-2002 MY
Workshop ManualYour experience will help others
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