Fan Secondary Low with Low Fan On
Your engine's secondary cooling fan isn't spinning when it should be, even though the engine is running hot. It's like having a backup air conditioner that refuses to kick in when the room gets too warm.
The ECU monitors secondary fan circuit voltage and current draw when commanding the fan on. It expects to see a voltage drop and current flow within a specific range when the coolant temperature exceeds the fan activation threshold. If voltage remains high or current is too low, the ECU detects an open circuit or resistance problem.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Fan circuit voltage when commanded ON | 0.5-2.0 volts (voltage drop across relay/fan) | Above 10 volts (open circuit) or no current draw |
| Coolant temperature for secondary fan | Below 200°F (93°C) | Above 210°F (99°C) with fan not running |
Code P1485 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, P1485 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.