P0691 Fan 1 Control Circuit Low

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P0691 Fan 1 Control Circuit Low

OBD-II Trouble Code Technical Description

Cooling Fan 1 Relay Control Circuit Low

What does that mean?

This is a generic powertrain diagnostic trouble code (DTC) applicable to all 1996-newer vehicles. Specific repair steps can vary from make/model.

The fans that are used to cool the engines radiator are run by electric motors. These motors are turned on and off by the powertrain control module (PCM) according to the readings from the engine coolant temperature sensor (ECT). In other words when the ECT reaches a predetermined temperature the PCM turns the fans on. Then when the ECT cools to a predetermined temperature the PCM turns the fans off.

The PCM controls the cooling fans by sending a ground signal to the cooling fan relay. The voltage on the signal circuit is high, around battery voltage, when not commanded on (not grounded). The opposite is true when commanded on (grounded), the voltage is somewhere near zero. DTC P0691 is set when the PCM senses the voltage low when the cooling fan 1 is off.

Symptoms & Severity of Code

Symptoms of a P0691 code may include:

  • Engine overheating
  • Check engine light on
  • The possibility of the engine overheating due to non-operational cooling fans is very probable so caution should be used if driving the vehicle when the conditions to set this DTC are present. It should be repaired as soon as possible.

    Causes

    Potential causes for this code to set are:

  • Faulty cooling fan relay 1
  • Blown cooling fan 1 fuse
  • Faulty PCM (rarely)
  • Diagnostic and Repair Procedures

    In my experience a blown cooling fan fuse is the most common cause of this DTC. Checking the fuse is a simple as locating, pulling it and looking at it. You can generally tell by visual inspection if a fuse is good or not. If the fuse is in fact blown, try replacing it with the correct amperage of fuse. If the fuse blows again the next question would be when did it blow?

    If the fuse failed immediately upon replacing it then there is a direct short somewhere between the fuse and the relay. If it failed when the engine reached operating temperature then the most likely cause is the cooling fan motor itself. With the engine and the ignition key off, carefully try and spin the fan blades by hand. They should spin freely, if it does not then the fan motor is frozen and will need replacement. If the fuse is good then the problem is most likely the cooling fan relay. If replacing the relay does not solve the problem suspect a faulty PCM.

    Be sure to use caution when working around components that are not only hot but also moving.

    Need help?

    Let us fix your problem. You are most welcome our diagnosis experts have in most cases the knowledge and skills to find the cause of the error code p0691 and to solve the problems.

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    "Delete Error Code Permanently, Disable DTC Error Code Function for p0691 in the ECU"

    In extreme cases, we even have the option to permanently remove the specific DTC p0691 and disable the function of the specific error code in the ECU. All other fault code functions will then continue to work to protect the engine. This is different from clearing an error code with a diagnostic device. We have the option to permanently remove the function of the specific error code, so that it never comes back. Also emergency running that occurs on the specific error code can be solved in most cases.

    Of course we prefer to first try to solve the cause of the error code, but sometimes the only solution is to permanently disable the DTC function of p0691.

    Make an appointment for permanent removal of p0691