P0691 and P0692: cooling fan 1 control circuit low and high

Older cars switched the cooling fan on and off. Modern ones vary its speed continuously, which is quieter, uses less power and holds coolant temperature far more precisely.

The price is complexity: a fan control module, a pulse-width-modulated command signal, and a feedback path — three things that can fail instead of one relay.

Code	Meaning
P0691	Fan 1 control circuit low
P0692	Fan 1 control circuit high
P0693, P0694	Fan 2 equivalents

The relay-based sibling: P0480 and P0481 cooling fan relay circuit.

Work out which system you have

Relay-switched: the fan comes on abruptly at one or two fixed speeds, and there is an audible step when it does. Relays exist in the fuse box.

Variable speed: the fan spools up and down gradually. There may be no relay at all, and a control module is mounted on or near the fan shroud.

If your vehicle sets P0691 or P0692, it is the second kind, and the relay-swap test has nothing to swap.

Where the module lives

Usually bolted to the fan shroud or the radiator support — directly in the airflow, low at the front of the car.

That means road spray, salt, stone strikes and, in some designs, standing water. Connector corrosion is the leading cause of these codes, ahead of module failure itself.

Salt and corrosion protection.

Symptoms

Fan never runs

Temperature normal at motorway speed, climbing in traffic. That pattern is the strongest single indicator in the whole cooling system.

The consequences of ignoring it are not modest: engine overheating diagnosis and P0217 engine over-temperature.

Fan runs at full speed constantly

The other failure direction, and much more noticeable because it is loud. Many control modules default to full speed when the command signal is lost — a deliberate failsafe, on the principle that too much cooling is safer than none.

So a fan roaring constantly is often the module doing its job correctly in response to a broken signal wire.

Fan continues after switch-off

Normal for a period after a hard drive. Not normal for hours, and it flattens the battery: parasitic battery drain diagnostics.

What to check

1. The connector at the fan module — corrosion, water, damaged pins.
2. The ground, usually a stud on the radiator support or body, in a corroded area.
3. Fuses, including the high-current one for the fan itself.
4. The command wire from the ECU, for chafing along the front of the engine bay.
5. The motor, which can seize or draw excessive current and take the module with it.
6. The coolant temperature signal, because a sensor reading cold means the fan is never requested: P0116 to P0119 coolant sensor performance.

That last point is worth its own emphasis. A fan that never runs may be a fan that was never asked to run. Verify the temperature reading is plausible before blaming the fan.

The air conditioning test still works

Switch on the air conditioning at idle. Nearly every vehicle commands the fan immediately when the compressor is requested, regardless of coolant temperature.

Result	Meaning
Fan runs	Fan, module and power path all work
Fan silent	Fault is in the fan side
Fan runs but temperature still climbs	Airflow blocked, or a coolant flow problem

That third row points away from electrics entirely — a blocked radiator core, a failed water pump or an air lock: water pump failure signs.

Log the temperature, not the gauge

Dashboard gauges are damped and sit mid-scale across a wide real range. Log actual coolant temperature while stationary at idle and watch for the plateau where the fan engages.

A healthy system shows temperature rising, then flattening or falling as the fan takes effect. No plateau means no cooling.

Temperature gauge fluctuating.

In what order

1. Test with the air conditioning on.
2. Verify the coolant temperature reading is plausible.
3. Inspect the module connector and ground.
4. Check fuses, including the high-current one.
5. Check the command wire for chafing.
6. Test the motor by powering it directly before replacing the module.
7. Log a stationary idle afterwards to confirm the fan engages and temperature responds.

The practical next step: pair an ELM327 adapter, open the free tier of the app and log coolant temperature while idling in a car park. The moment the fan cuts in, and whether temperature actually falls, is the entire test.