Description of the P0691 fault code.
OBD2 Error Codes

P0691 Cooling Fan 1 Relay Control Circuit Low

26.05.2022 /

P0691 – OBD-II Trouble Code Technical Description

DTC P0691 indicates the cooling fan 1 motor control circuit voltage is too low.

What does the fault code mean P0691?

DTC P0691 indicates that the cooling fan 1 motor control circuit voltage is too low compared to the manufacturer's specifications. This means that the vehicle's powertrain control module (PCM) has detected that the cooling fan 1 motor circuit voltage is lower than expected.

Fault code P0691.

Possible reasons

Trouble code P0691 can be caused by the following reasons:

  • Fan motor malfunction: Problems with the fan motor itself, such as open or shorted windings, can cause low voltage in the control circuit.
  • Poor electrical connection: Loose contact or corrosion in connectors, wires or connections between the motor and PCM can cause low voltage.
  • Fan relay failure: If the relay that controls the fan motor is not functioning properly, it may result in low voltage in the control circuit.
  • Problems with PCM: Faults or damage in the PCM, which controls the engine and cooling system, can cause P0691.
  • Problems with the temperature sensor: A faulty coolant temperature sensor or its connections can also cause P0691.
  • Electrical problems in the system: A short circuit or open circuit in the control circuit, such as a damaged wire or fuse, may also cause this error.

What are the symptoms of a fault code? P0691?

Symptoms when trouble code P0691 is present may include the following:

  • Engine overheating: Insufficient engine cooling due to improper operation of the cooling fan can lead to engine overheating.
  • Increased coolant temperature: Failure to activate the fan may result in elevated coolant temperatures in the cooling system.
  • Performance degradation: When the engine overheats, vehicle performance may be reduced due to the activation of a protection mode that limits engine operation.
  • Warning indicators appear: The "Check Engine" light on the instrument panel may come on, indicating a problem with the system.
  • Inactive cooling fan: The cooling fan may not turn on when a certain temperature is reached or may not operate properly.
  • Overheating in traffic jams or congestion: When parked in traffic or in a traffic jam, the car may begin to overheat due to insufficient cooling system performance.
  • Air conditioner performance deterioration: Insufficient cooling by the coolant can also affect the operation of the air conditioner that uses the coolant for cooling.

If you experience the above symptoms, it is recommended that you contact a qualified auto mechanic to diagnose and repair the problem.

How to diagnose a fault code P0691?

To diagnose DTC P0691, you can follow these steps:

  1. Visual inspection: Check the wiring, connectors and connections associated with the cooling fan motor. Pay attention to possible damage, corrosion or broken wires.
  2. Checking relays and fuses: Check the condition of the relay that controls the fan motor and the fuses associated with the cooling system. Make sure the relay activates when needed and that the fuses are intact.
  3. Using the Diagnostic Scanner: Connect the vehicle to an OBD-II diagnostic scanner to read DTC P0691 and other related codes, and check the cooling system performance parameters in real time.
  4. Fan motor testing: Check the operation of the fan motor by supplying voltage directly from the battery. Make sure the motor is functioning properly.
  5. Temperature sensor test: Check the operation of the coolant temperature sensor. Make sure it is reporting correct engine temperature data.
  6. Checking the generator and battery: Check the condition of the alternator and battery, make sure the alternator is producing enough voltage to charge the battery.
  7. Additional tests as needed: Depending on the diagnostic results, additional tests may be required, such as checking the cooling system for leaks or testing the accelerator pedal position sensor (if applicable).
  8. Contact a specialist: If the cause of the P0691 code cannot be determined, or if specialized tools or equipment are needed, it is recommended that you contact a qualified auto mechanic or auto repair shop for further diagnosis and repair.

Carrying out a thorough diagnosis will allow you to identify the cause of the P0691 error and correct the problem.

Diagnostic errors

When diagnosing DTC P0691, the following errors may occur:

  1. Misinterpretation of symptoms: Sometimes symptoms such as engine overheating or air conditioning malfunction can be mistakenly interpreted as the cause of low voltage in the cooling fan control circuit.
  2. Insufficient checking of electrical connections: Incorrect or incomplete inspection of wiring, connectors and connections may result in missing a real problem in the electrical circuit.
  3. Ignoring other related DTCs: P0691 can be associated with other trouble codes such as coolant temperature sensor or fan relay errors. Ignoring these codes may result in an incomplete diagnosis of the problem.
  4. Insufficient testing of relays and sensors: The operation of the fan relay, temperature sensor and other cooling system components must be thoroughly tested to eliminate them as causes of the P0691 code.
  5. Skipping Alternator and Battery Testing: Insufficient attention to the condition of the alternator and battery can lead to missing a problem related to the vehicle's power supply.
  6. Incorrect reading of scanner data: Failure to read the diagnostic scanner correctly may result in misinterpretation of symptoms and incorrect resolution of the problem.

To avoid these errors, it is important to carry out all necessary diagnostic steps carefully and consistently.

How serious is the fault code? P0691?

Trouble code P0691, which indicates the cooling fan 1 motor control circuit voltage is too low, can be a serious problem, especially if left unattended or not corrected promptly. The following are some reasons why this trouble code may be considered serious:

  • Engine overheating: Low voltage in the cooling fan control circuit may result in insufficient engine cooling, which may cause engine overheating. An overheated engine can cause serious damage and costly repairs.
  • Engine damage: If the engine overheats for a long time, serious damage may occur, such as damage to the cylinder head, piston rings, or other internal engine components.
  • Inability to use the car: If the engine overheats due to insufficient cooling, the vehicle may be unable to operate normally, which may result in traffic stops and a dangerous situation.
  • Possible additional damage: In addition to engine damage, overheating can also cause damage to other vehicle systems such as the transmission, oil seals, and seals.

So, although the P0691 trouble code itself is not a fatal error, ignoring it or not repairing it can lead to serious consequences for the vehicle and its owner. Therefore, it is recommended that you take steps to diagnose and resolve this issue as soon as possible.

What repair will help eliminate the code? P0691?

Resolving trouble code P0691 depends on the specific cause of the problem. The following are possible actions and repair procedures to resolve this code:

  1. Checking and replacing damaged wires and connectors: If damaged wires or connectors are found, they must be replaced or repaired.
  2. Fan relay replacement or repair: If the fan relay does not function correctly, it must be replaced with a new one or repaired.
  3. Checking and replacing fuses: If the fuses associated with the cooling system are broken, they should be replaced with new ones.
  4. Fan motor diagnostics and repair: If the fan motor does not function correctly, it must be checked and replaced if necessary.
  5. Checking and replacing the temperature sensor: If the coolant temperature sensor does not provide correct data, it must be replaced with a new one.
  6. Diagnose and repair problems with the charging system: If the low voltage problem is with the alternator or battery, they will need to be checked and, if necessary, replaced or repaired.
  7. PCM Software Update (if needed)Note: In rare cases, a PCM software update may be required to correct cooling system control problems.

Once the appropriate repairs have been made, the cooling system should be tested and diagnosed using a diagnostic scan tool to confirm that the problem has been successfully resolved and the P0691 trouble code no longer returns. If the cause of the malfunction cannot be determined or corrected independently, it is recommended that you contact a qualified auto mechanic or service center for further diagnosis and repair.

How to Diagnose and Fix P0691 Engine Code - OBD II Trouble Code Explain

P0691 – Brand-specific information

Trouble code P0691 indicates that the cooling fan motor control circuit voltage is too low, and can be found for several common vehicle brands:

Each manufacturer may have its own way of interpreting fault codes, so to accurately determine the cause and resolve the problem, it is recommended that you consult the service manual for your specific vehicle brand or contact a qualified auto mechanic.

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