P0691: Fan 1 Control Circuit Low

The engine module switches the radiator fan relays (or the input of a PWM fan module) through output drivers and checks each control circuit electrically. GM sets a short to ground or voltage at 0.5 Ω or less after 50 of 63 samples, with the lamp after two trips; GM Europe's 2011 Saab 9-5 covers P0691–P0696 with relay assignments, the Saab 9-4X's PWM fan module reacts within 1 s. P0691 means the fan 1 control circuit is shorted to ground. GM fixed a related problem with bulletin 16-NA-123, Ford with SSM 47999 for the 6.7 L diesel. The former title 'Cooling Fan 1' was shortened to the J2012 wording, as for P0480.

Symptoms

• Check engine light (GM after two trips)
• Fan runs constantly or not at all, depending on circuit design
• Rising coolant temperature in traffic or with A/C on
• A/C may be switched off to protect the engine

Most likely causes

• Control wire to fan relay or module shorted to ground (chafing)
• Water or corrosion in fan or relay connector
• Fan relay faulty (coil shorted or low-resistance)
• Engine module driver faulty

What to check, in order

Start with the simplest. You can tick off each step.

1. With the engine cold, check the coolant level; never do this when the system is hot
2. With the connector unplugged, check whether the signal wire is making contact with ground.
3. Check the actual temperature in live data
4. Make sure the fan comes on when it should
5. Check the thermostat and connector
6. Measure the sensor and replace it if its readings do not make sense

Good to know

• Repair difficulty: easy
• It affects emissions.

What each character of P0691 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 6: Control modules and outputs
• 91: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0691?

Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

What causes code P0691?

The most common causes are: control wire to fan relay or module shorted to ground (chafing); water or corrosion in fan or relay connector; fan relay faulty (coil shorted or low-resistance).

Related codes

• P0480Fan 1 Control Circuit
• P0692Fan 1 Control Circuit High
• P0693Fan 2 Control Circuit Low
• P0695Fan 3 Control Circuit Low
• P0483Fan Rationality Check
• P0494Fan 1 Underspeed

Sources

• law.cornell.edu: 13 CCR 1968.2
• gsi.ext.gm.com: 18OBDG03A Engine Diagnostics
• gsi.ext.gm.com: 25OBDG03A
• saabwisonline.com: dtc p0480 p0482 or p0691 p0696

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.