P1805: Transmission 4-Wheel Drive High Indicator Open Circuit

P1805 is a powertrain code that points to an open circuit in the 4-wheel drive high indicator circuit, which sits within your transmission system. The indicator circuit is responsible for telling the vehicle's computer when 4WD high mode has been engaged. When the PCM detects that the signal from this circuit is missing or broken, it logs P1805 and may illuminate a warning light on the dash.

The most common causes are a broken or corroded wire in the indicator circuit harness, a damaged connector at the transfer case or dashboard cluster, or a failed indicator switch. Because this is an open circuit fault rather than a short, the issue is typically a physical break in the wiring rather than an electrical overload. Checking the connector and wiring between the transfer case and the PCM is the right place to start, looking for corrosion, chafing, or broken terminals.

P1805 carries a medium severity rating, meaning it is not an immediate safety threat but should not be left unresolved. You may find that your 4WD high indicator light does not illuminate even when the system is active, which removes useful driver feedback. Get the wiring inspected and repaired before relying on 4WD in conditions where you need to know it is engaged.