B1349

Code

Other B — Body

Heated Backlite Relay Short To Battery

Brand: Other

Type: B — Body

Views: UK: 20 EN: 22 RU: 20

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Short in relay control or power feed to battery positive
Faulty/heavily corroded relay contacts stuck closed
Wiring harness damage (chafing, pinched insulation) causing conductor to contact B+
Faulty body control module or relay driver output stuck high
Blown or bridged fuse, poor ground connection or connector corrosion

Symptoms

Rear window defogger or heated backlite operates continuously or intermittently without switch input
Related fuse(s) blowing repeatedly
Battery draining when vehicle is off
Relay or wiring unusually hot
Possible instrument panel indicator for defogger on when switched off

What to check

Visual inspection of relay, fuse, connectors and wiring for heat damage, corrosion, melted insulation or pinched wires
With ignition off, inspect fuse for the defogger circuit and check for blown fuse
Check whether the defogger switch or dash indicator is responding (on/off)
Use a DVOM to measure voltage at relay control and switched terminals with switch off and with switch on
Measure resistance of relay coil (remove relay) and compare to specification
Perform wiggle test on wiring harness while monitoring voltage and fuse status

Signal parameters

Battery voltage at rest: ~12.0–12.8 V (engine off); with engine running: ~13.5–14.8 V
Relay coil resistance (typical): 50–200 ohms (vehicle-specific)
Switched defogger circuit current when active: can be 5–30 A depending on grid and vehicle (measure with clamp meter)
Control signal: normally low (ground) or low voltage when off; should not show constant battery voltage at control input when off

Diagnostic algorithm

Record customer complaint and confirm condition (defogger on/off behavior, fuses blown)
Visually inspect relay, socket, connectors and harness near the rear window and under the dash for damage or corrosion
With ignition off, remove the heated backlite relay and inspect contacts for welding or melting; measure coil resistance on relay — replace relay if out of spec or visually damaged
Check fuse(s) in the defogger circuit; if blown, do not repeatedly replace without diagnosing short
With relay removed and ignition off, check for battery voltage on the relay’s control and switched terminals; there should be no B+ present at the control terminal when switch is off
If B+ is present on control when relay removed, trace wiring back toward the switch and body control module to find a short to battery — isolate sections by disconnecting connectors and rechecking voltage
If control voltage disappears when a connector is disconnected, inspect that harness segment for chafing or connector faults; repair insulation or replace wiring as needed
If short persists with harness isolated, suspect body control module or relay driver output; verify inputs to module and consult wiring diagrams before replacing module
After repairs, replace relay and any fuses, then verify normal operation in multiple ignition states and that no DTCs return

Likely causes

Damaged/harness short between relay control wire and battery positive
Stuck or welded relay contacts allowing constant B+ to heater circuit
Faulty relay driver in the vehicle control module

Fault status

⚠️ Status

Stored when the heated backlite relay circuit is detected with battery voltage present where the control circuit should be off (short to B+). May set when the relay is commanded off but the circuit remains energized or when excessive current is detected due to a short.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-1.5 hours