Faulty fan relay or fan control module; Damaged wiring to the fan control circuit, such as chafing or a short to ground; Corroded, loose or damaged connector at the relay, fan or control unit; Blown fuse or poor power or earth supply to the fan circuit; Failed fan motor drawing excess current or shorting internally; Internal fault in the engine control unit driver.

P0691

Fan 1 Control Circuit Low.

Generic
Powertrain
Generic code
High severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
6: AreaComputer and output circuits
91: FaultThe specific fault in that area

What it means

P0691 means the engine control unit has detected a low voltage or signal state in the control circuit for cooling fan 1 that does not match what it commanded. The fault is set when the circuit reads low, for example shorted to ground, when it should be high, or when the driver or relay circuit is not responding correctly. How the fan is controlled (relay, module or direct driver) depends on the vehicle.

Symptoms

Engine cooling fan not running, or running constantly at full speed
Engine temperature rising or overheating in traffic or when idling
Air conditioning performing poorly or cutting out at idle
Engine warning light on
Temperature gauge reading higher than normal

Possible causes

Faulty fan relay or fan control modulelikely
Damaged wiring to the fan control circuit, such as chafing or a short to groundlikely
Corroded, loose or damaged connector at the relay, fan or control unitlikely
Blown fuse or poor power or earth supply to the fan circuitpossible
Failed fan motor drawing excess current or shorting internallypossible
Internal fault in the engine control unit driverrare

How to diagnose

Read all stored and pending codes and note the freeze frame data, including coolant temperature and vehicle speed at the time of the fault.
Check the coolant level and look for other cooling system faults, as the fan may be commanded on for a genuine reason.
Inspect the fan fuses, relay, wiring and connectors for heat damage, corrosion, chafing and water ingress.
Use a scan tool with bidirectional controls to command the fan on and off and see whether it responds.
Check power and earth supplies at the relay or fan connector with a multimeter, using the wiring diagram for the specific model.
Test the control circuit for a short to ground by checking resistance to earth with the connector disconnected.
Test the relay and, where fitted, the fan control module, and check the fan motor current draw against the manufacturer's specification.
Clear the code and retest to confirm the fault does not return.

How to fix

Repair or replace damaged wiring and fix any short to ground in the control circuit.
Clean or replace corroded or damaged connectors and terminals.
Replace a faulty fan relay or fan control module.
Replace a blown fuse only after finding and fixing the cause of the overload.
Replace the cooling fan motor if it is faulty or drawing excess current.
Repair or replace the engine control unit only once all wiring and components have been proven good.

Can I keep driving?

High severity

Avoid driving until the fan is working, because without it the engine can overheat quickly in traffic or at idle and suffer serious damage. If you must move the car, keep trips short, watch the temperature gauge closely and stop if it rises.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.