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P0691 is a diagnostic trouble code (DTC) for "Fan 1 Control Circuit Low P0692 Fan 1 Control Circuit High". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
The P0691 code appears when the powertrain control module (PCM) has detected an inappropriate level of voltage in the electric cooling fan's control circuit. The level can be too high or too low.
P0691 is an OBD-II generic code triggered when voltage varies by more than 10% of the vehicle manufacturer's explicit reference voltage.
The code may have several reasons for appearing:
Typically, the P0691 code has almost no symptoms except the illumination of the check engine light, though an engine may overheat because of this issue and any air conditioning systems may operate less effectively.
P0691 is diagnosed with an OBD-II scanner, digital ohm meter and an infrared thermometer can be very useful. Diagnosing this can be somewhat challenging without knowing the manufacturer's specs regarding cooling fans for the engine and the air conditioner. The mechanic or technician will then use a scanner to activate the engine fan and check voltage and grounding of the fan motor. No voltage means the system fuses must then be tested, and if the fuses are acceptable, the fan relay must be checked. The voltage at the connector must be within manufacturer specs.
The engine temperature readings must then be tested and if not within the manufacturer specs, it is likely a faulty engine coolant temperature sensor. Typically, this series of tests will reveal the source of the code, and the technician will then repair any open or shorted circuitry as detected by the diagnostics before rechecking with the scanner.
Any mistakes in diagnosis tend to come from the replacing of cooling fan motors prior to running the multiple steps of diagnosis. There are primary fans and some secondary fans, and the mechanic has to run a full test before simply replacing the primary fan motor.
The P0691 code does not prevent the car from running, but some vehicles can overheat at idle when this problem persists. Poorly operating air conditioning is also undesirable and is a common consequence of this code.
To address the P0691 code, the following repairs are typically used:
PCM issues can be an issue, but this is a rarity. You may also have to run diagnostics identical to those above on any secondary cooling fan systems and their associated circuitry. Controlled by dual systems, they are most often meant to provide air to the air conditioning systems and are run via sensors relating to the air conditioning and not the engine coolant sensors. You may need to track the system that activates a secondary or cooling fan to determine the source of the problem.
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