Heated Wind Shield Relay Short to Vbatt (changed from Failure 2/6/97)
The heated windshield relay circuit is stuck in the "on" position, sending constant battery voltage instead of switching on and off as needed. Think of it like a light switch that's jammed in the on position—it keeps drawing power even when you don't want it to.
The ECU monitors the voltage and current flow through the heated windshield relay control circuit. It expects the relay to toggle between ground (off) and open (on) states based on driver input. A short to Vbatt means the relay contacts or wiring are stuck at battery voltage instead of cycling normally.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Relay Control Voltage | 0V (off) to switching pattern (on/off cycle) | Continuous Vbatt (~12-14V) with no switching |
| Relay Coil Current Draw | 0-500mA intermittent | >500mA continuous or stuck high |
Code B2109 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.
Once the fault is repaired, B2109 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.