The evolution of sensors and monitoring equipment has enhanced over the past 10 years. In fact, on many newer vehicles, a new battery temperature sensor is a critical component that helps the vehicle maintain a charge in the battery. Since several mechanical components and features are being replaced by electrically controlled and powered units, having a fully charged battery is becoming more critical to vehicle operation. It's for this purpose that these newer vehicles have battery temperature sensors.
As the name implies, the job of the battery temperature sensor is to detect the temperature of the battery so that the charging system voltage can be supply power to the battery as needed. Not only does this process ensure that the battery does not overheat, but it also reduces drag from the electrical system; increasing overall efficiency for the vehicle. In times when the battery's temperature is cool it triggers the electrical system (alternator) to increase the flow of electricity to the battery. When the temperature is high – the reverse applies.
Like any other sensor, the battery temperature sensor is subject to wear and tear and prone to damage. In most cases, issues with the battery temperature sensor are caused by corrosion or collection of dirt and debris, which impacts the sensors ability to effectively monitor and relay temperatures. In some cases, simply removing the battery and cleaning the sensor and electrical harness connector solve the issues. Other instances require the replacement of this component.
Part 1 of 2: Determining the symptoms of a damaged battery temperature sensor
The battery temperature sensor is designed to last for the lifespan of the vehicle but debris or contamination cause this component to break or wear out prematurely. If the battery temperature sensor is damaged or has failed, the vehicle typically displays a few common warning signs or symptoms alerting the driver that an issue exists. Some of the common symptoms of a damaged battery terminal sensor include:
The engine's RPM curve is surging: Under most circumstances, the vehicle's battery has no impact on the operation of the engine after the car is started. In fact, power is supplied to other components from the alternator or voltage regulator. However, if the battery temperature sensor is damaged, it can cause a disruption in the electrical flow to the ignition system. The battery has low voltage: When the temperature sensor is unable to accurately read the battery temperature, it triggers an OBD-II error code which commonly disables the voltage system coming from the alternator to the battery. If this occurs, the battery's voltage slowly drains as it has no source of recharging. If this goes unrepaired, the battery eventually drains and is unable to start the vehicle or power accessory items if the car's engine is turned off.
Check Engine Light is illuminated on dash: Typically when error codes are stored in the ECM, the Check Engine Light will be triggered and light up on the dashboard. Under some circumstances, it also triggers the battery light on the dash. The battery light typically indicates that there is a charging issue with the battery, so it may also be a sign of other electrical problems. The best way to determine the precise cause of the warning light is to download the error codes stored in the ECM by using a professional digital scanner.
If you notice any of these warning signs, it's recommended you plug the diagnostic tool into the port under the dash to download the error codes. Typically, when the battery temperature sensor is damaged, there will be two different codes displayed. One code indicates that the battery temperature sensor is shorting in and out of circulation for short periods of time while the other code indicates a total loss of signal.
If the sensor is shorting out periodically, it's usually caused by dirt, debris, or a bad connection from the sensor to the electrical harness. When the signal is lost, it's often due to a bad sensor that needs to be replaced.
The battery temperature sensor located underneath the battery on most vehicles. It's a good idea to purchase a service manual for your vehicle to learn the precise steps for locating and replacing this component on your vehicle, as it can vary based on individual vehicles.
Part 2 of 2: Replacing the battery terminal sensor
On most domestic vehicles, the battery temperature sensor is located underneath the battery box and is placed directly below the battery. Most batteries develop excessive heat towards the bottom of the core and often in the middle of the battery, which is why the temperature sensor is located in this position. If you've determined that the issues you're experiencing are due to a bad battery temperature sensor, gather the appropriate tools, replacement parts and prepare the vehicle for service.
Since the battery needs to be removed, you don't have to worry about raising the vehicle to complete this job. Some mechanics prefer to raise the vehicle and complete this job from below if the battery temperature sensor is connected to electrical harnesses underneath. Due to these reasons, it's a great idea to purchase a service manual for your exact vehicle; so you can read up and develop a plan of attack that is best suited for your individual application and your availability of tools and supplies.
According to most service manuals, this job is rather simple to complete and should only take about one hour. However, since the bad battery temperature sensor probably triggered an error code and is stored inside the ECM, you'll need a digital scanner to download and reset the ECM before trying to start the vehicle and test the repair.
Replacement battery temperature sensor
Socket set and ratchet (with extensions)
Boxed and open end wrenches
Note: In some cases, a new harness is needed as well.
Step 1: Remove air filter housing and engine covers. On most vehicles that have a battery temperature sensor, you'll have to remove engine covers and air filter housings. This allows you to gain access to the battery and the battery box where the temperature sensor is located. Follow your manufacturer’s service manual steps for removing these components; proceed to the next steps below.
Step 2: Loosen air filter connections to throttle body and remove. After you've removed the engine cover, you'll need to remove the air filter housing that also covers the battery box. To complete this step, loosen the clamp that secures the filter to the throttle body first. Use an end wrench or socket to loosen the clamp, but do not fully remove the clamp. Wiggle the throttle body connection loose with your hands, making sure not to damage the filter housing. Using both hands, hold onto the front and back of the air filter housing and remove it from the vehicle. Typically, the housing is attached to button clips that pull out of the vehicle with enough pressure. Always refer to your service manual for exact instructions as some vehicles have bolts that need to be removed first.
Step 3: Remove positive and negative battery cables from the terminals. The best way to complete this step is to use an end wrench to loosen the battery cables. Start with the negative terminal first, then remove the positive cable from the battery. Place the cables aside.
Step 4: Remove battery harness clamp. Typically, the battery is secured to the battery box through a clamp that often has one bolt.
In most cases, you can remove this bolt with a socket and extension. Remove the clamp and then remove the battery from the vehicle.
Step 5: Locate and remove battery temperature sensor. Most of the time, the battery temperature sensor is placed flush inside the bottom of the battery box.
It is attached to an electrical connection and can be pulled through the hole in the battery box for easy removal. Simply press the electrical harness tab down and pull the sensor from the harness gently.
Step 6: Clean the battery temperature sensor. Hopefully, before you completed this process, you were able to download the error codes.
If the error code indicated a slow and gradual lost signal, clean the sensor along with the electrical harness, reinstall the unit and test the repair. If the error code indicated a complete loss of signal, you’ll need to replace the battery temperature sensor.
Step 7: Install the new battery temperature sensor. Attach new sensor to the electrical harness and reinsert the battery temperature sensor inside the hole at the bottom of the battery box.
Verify that the temperature sensor is flush on the battery box just as it was when you removed it earlier.
Step 8: Install the battery. Reattach battery cables to the correct terminals and reattach the battery clamps.
Step 9: Install battery cover and air filter back onto the vehicle. Secure throttle body attachment and tighten clamp; then install engine cover.
Replacing the battery temperature sensor is an easy jobs to complete. However, different vehicles may have unique steps and different locations for this component. If you don’t feel comfortable performing this repair on your own, have one of YourMechanic’s certified mechanics complete the battery temperature sensor replacement for you.
This article originally appeared on YourMechanic.com as How to Replace a Car Battery Temperature Sensor and was authored by Tim Charlet.