P0691 – Engine coolant blower motor 1 -short to earth

Tapley Mitchell

By Tapley Mitchell (Contact Me)
Last Updated 2019-09-19
ASE Mechanic

CodeFault LocationProbable Cause
P0691 Engine coolant blower motor 1 -short to earth
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Wiring short to earth, engine coolant blower motor, ECM

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What Does Code P0691 Mean?

If you have gotten this code, it means the cooling fan, which is located on the backside of the radiator, is inoperable. This is caused by one of two things. Either the fan works but does not work as well as it should; or the fan is not in working condition. The reason this code happened is because the ECM or Engine Control Module, has detected that the voltage has dropped to the bottom 10% of the parameters set by the manufacturer. When it gets that low, it will send a code, warning you of the drop.

What are the common causes of code P0691 ?


Common causes of this code error could be any of the following four reasons:

  • The cooling fan motor
  • Faulty relay
  • Poor connections
  • Blown fuse

Do not replace the cooling fan immediately without doing some of the tests below as there could be an inexpensive fix.

What are the symptoms of code P0691 ?

Symptoms of a cooling fan problem may be poor air conditioning performance, especially when parked and overheating, or you may notice rising engine temperatures, especially at low speeds and stop and go traffic.

How do you troubleshoot code P0691 ?

With any trouble code that refers to an electrical circuit error, always check the battery first. Step two- check the battery first. That’s how important it is! To check the battery, you will need a volt meter that can read DC voltage. Place one lead on the positive terminal and the other lead on the negative terminal. You should have 12.6V DC with the car off and 13.8- 14.5 V with the engine running.

Next is to check for a blown fuse. Locate the f use box, which is normally in the engine bay. On the lid of the fuse box there should be a diagram, indicating which fuse to inspect. If there is not a diagram check your owner’s manual, or reference the internet for a diagram. Pull the fuse out of the fuse box. Set your digital multi meter to the ohms setting. The symbol of ohms looks like a horse shoe. Now put one lead on each exposed prong. The resistance value or measurement you are taking should read less than .5 ohms. However, your meter may also have some resistance in its circuits. If it reads higher than .5 ohms, co connect your two leads to each other and subtract that value from the fuse measurement value. If the value is higher than .5 ohms, replace the fuse with a brand new one and the problem should be gone. If the value is .5 ohms, let’s move to the next step.

In that same location, we will move on to checking the relays. Look for the label “fan relay”. If the relays are somewhere else, check your owner’s manual for their location. Some vehicles will have one relay, others will have two. This will also be done with the ohms setting on the multi meter and a pair of mini jumper cables. Mini jumper cables are cheap and can be bought from Amazon or Wal-Mart. Now check the labels that are on the lid to find the relays. The most common pin will be a Bosch style 5 pin relay. Pull the relay out and there may be numbers on the bottom of the relay. The 5 pins will be labeled 85, 86, 87, 87a, and 30. Using the mini jumpers and a 9-volt battery, connect one lead to pin 85 and the other end of the lead to one side of the battery. It does not matter which side of the battery you use. Connect your remaining lead to the battery side and then complete the circuit by tapping the last lead on pin 86. You should hear a clicking noise inside the relay.

Next, take the ohm meter and measure pins 87a and 30. The reading should be close to 0 ohms and is typically not used in the fan relay circuit, so check the resistance to be sure. Increased resistance here could indicate corrosion on the inside of the relay.

Now connect the ohm meter to pins 87 and 30 and keep them connected. Connect the 9-volt battery to pins 85 and 86 and leave these connected, too. Check the readings for pins 87 to 30. They should be less than one ohm. If it is more than one ohm, this may be the voltage drop you are looking for. If everything checks out, reinstall the relay and find the connector the cooling fan plugs in to.

If you have made it this far, it is time to check the cooling fan motor. For this test, the ignition needs to be set to the “on” position. You can do this with the engine running or the engine off, it doesn’t matter. Be sure to set your air conditioning to high or max a/c setting available. This will tell the computer to turn the fans on. Next, unplug the fan, and switch your multi meter to volts. You should see twelve volts or greater with the a/c on. If you have two fans, compare the voltage between the two fans. If voltage here is low, you may have a short to ground in the wiring harness or a bad resistor module. This controls the speed of the fan and is commanded by the ECU.

If everything looks good here, we can move on to testing the fan. You will do this by using the mini jumper cables to connect one clip to each pin inside the fan connection. There should only be two pins in the plug. If there are more than two, your resistor may be inside the fan motor housing. A wiring diagram for your exact vehicle can tell you which pins to connect. These are easily found by googling the year, make, and model of your vehicle followed by the words, “wiring diagram”. Once you have your mini jumpers connected to the fan pigtail, make sure all wires, tools, fingers, clothing and hair are clear of the fan blades. Connect the other ends of the mini cables to the car battery. The motor of the fan should kick on and run at full speed. If you have two fans, compare the speeds of each fan. If fan one is slower than fan two, then you will need to replace the cooling fan. Sometimes you can order just the motor, but more often than not, you will have to order the entire assembly which will replace both fans.

Codes Related to P0691

  • P0692 – fan one control circuit high
  • P0480 – cooling fan one control circuit malfunction
  • P0482 – cooling fan malfunction

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