Transmission Automatic 4-Wheel Drive Indicator (Lamp) Circuit Short To Battery
The 4WD indicator lamp circuit is shorted directly to battery power, causing the ECU to detect constant high voltage instead of the expected control signal. Think of it like a light switch stuck in the ON position—the lamp stays lit even when it shouldn't be.
The ECU monitors the voltage level of the 4WD indicator lamp circuit, expecting it to toggle between low (lamp off) and high (lamp on) states based on transmission mode commands. When a short to battery occurs, the circuit remains at battery voltage continuously, exceeding normal thresholds and triggering the fault code.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Lamp circuit voltage | 0V-5V controlled switching | Stuck at battery voltage (12V+) |
| Circuit resistance | Varies with control state | Near zero ohms (direct short) |
Code P1874 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P1874 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.