P0691 Cooling Fan 1 Control Circuit Low

P0691 points to a low condition in the cooling fan 1 control circuit. The controller sees fan 1 control voltage or feedback below the expected range.

Code details

Generic OBD-II · P0

System: Computer
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace the fan motor before checking the relay, fuse feed, ground, control circuit, and command conditions.

Symptoms of P0691

Check-engine light, sometimes with several unrelated codes at once.
Warning lights, a no-start, or intermittent electrical faults.
Communication or module-reset problems on a scan tool.

Common causes of P0691

Low battery voltage, poor grounds, corroded connectors, or blown fuses.
Wiring or network (CAN bus) faults between modules.
A module software/programming issue, or rarely a failed controller.

Useful checks before replacing parts

Check fan 1 command, control voltage, relay or module output, fan current draw, coolant temperature, A/C request, battery voltage, and freeze-frame data.
Inspect fan 1 relay, fuse feed, ground path, motor resistance, connector heat damage, control wiring, and fan module terminals for corrosion or melting.
Command fan 1 at different speeds where supported and verify voltage, current, and actual fan operation under load.

Related OBD-II codes

These nearby computer entries can help compare wording and pin down the fault area.