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Know How – Expert Edition – Heated Screens and Battery State

28 Jul 2021


With Tim Stock

Tim is well-known in the automotive aftermarket for his wealth of experience and expertise in all things repair-related. From lending a helping hand to installers through technical support to leading regular seminars, Tim’s name has become synonymous with Know How. In this Expert Edition article, he will be turning his keen eye for automotive to the relationship between heated screen malfunctions and battery state to help provide a solution when these systems go awry. To find out more about NAPA batteries, contact the NAPA batteries helpline at 0161 971 5001.


Heating-related issues are a fixture of colder months, and many technicians are especially stumped by a recurring issue with non-functional heated front screens and mirrors. The problem may manifest in the electrical system, but it stems from the battery. This guide will explain why a battery’s state can lead to heated screen issues.


Heated screens are controlled by the Body Control Module (BCM), which retrieves operating information from the medium-speed Controller Area Network (CAN) bus, including fault codes. If the issue is being caused by your battery, the following will be true:

  • No fault codes will be present on the BCM.
  • No door module faults codes will be recorded by the CAN.

Additionally, the automatic temperature control module for heating both the screen and the mirrors will show a functional switch status.


A simple battery test is all it takes to get to the root of the issue. When looking at the results of said test, there are two key areas for determining problem cause:

  • State of Health (SOH)
  • State of Charge (SOC)

Both of these data streams will likely show battery issues, which means a replacement is needed to restore heated screen and mirror function. As increased demand is placed on modern electrical systems, it is important to test the battery to determine both SOH and SOC before carrying out an electrical diagnostic process.


Heated screen issues have been found to affect the operation of stop-start systems that require a minimum SOC of above 80%.

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