What Does P0691 Mean?
The PCM has detected a low voltage condition on the cooling fan 1 control circuit. This means the circuit that drives the primary engine cooling fan is being pulled to ground, indicating a short in the wiring or the fan motor itself. The cooling fan may run continuously, not run at all (if the fuse blew), or behave erratically. The driver may notice engine overheating, the fan running at full speed constantly, or a blown cooling fan fuse.
Safety Warning
If the cooling fan is not operating, the engine can overheat rapidly, especially in stop-and-go traffic or while idling. Overheating can cause head gasket failure, warped cylinder head, or engine seizure. Do not drive in heavy traffic until the cooling fan is verified operational. Monitor the temperature gauge closely.
Common Causes
30%
Cooling fan motor with internal short drawing excessive current
25%
Short to ground in the fan control circuit wiring
20%
Failed cooling fan relay stuck closed or with shorted coil
15%
Cooling fan resistor or speed controller module failure
10%
PCM fan driver circuit shorted
Diagnostic Steps
1
Check the cooling fan fuse first; a blown fuse often accompanies a low-circuit condition. If blown, do not simply replace it without finding the root cause.
2
Disconnect the cooling fan motor connector and measure the motor winding resistance; compare to spec (typically 1-5 ohms). A very low reading indicates an internal short.
3
With the fan disconnected, check the control circuit wiring from the relay/PCM to the fan connector for shorts to ground; resistance should be OL.
4
Inspect the fan relay by removing it and checking coil resistance (60-100 ohms) and contact resistance (should be OL when de-energized, near 0 when energized manually).
5
If the vehicle uses a fan speed controller module, check for diagnostic codes specific to that module and inspect it for heat damage or melted connectors.
Estimated Repair Cost
$75 - $600
Parts + labor, varies by vehicle and location
The PCM has detected a low voltage condition on the cooling fan 1 control circuit. This means the circuit that drives the primary engine cooling fan is being pulled to ground, indicating a short in the wiring or the fan motor itself. The cooling fan may run continuously, not run at all (if the fuse ...
The most common cause of P0691 (Fan 1 Control Circuit Low) is: Cooling fan motor with internal short drawing excessive current
Typical repair costs for P0691 range from $75 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
If the cooling fan is not operating, the engine can overheat rapidly, especially in stop-and-go traffic or while idling. Overheating can cause head gasket failure, warped cylinder head, or engine seizure. Do not drive in heavy traffic until the cooling fan is verified operational. Monitor the temperature gauge closely.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0691 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Engine Cooling System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
