Body Electronics

The BCM controls virtually EVERY electrical function on the vehicle and problems within the BCM (or its associated fuse box) will cause mis-operation of vehicle electrical functions. When diagnosing electrical problems on vehicles fitted with BCM, it is vital to appreciate the relationship between the BCM and its associated electrical fuse box.


  • Specific BCM fault symptoms include mis-operation of headlights, door locks, electric windows, fuel filler flap, indicators, sun roof. These faults may be intermittent.
  • Erroneous fuse failure codes are also symptoms of BCM failure (if fusebox has been changed).
  • Intermittent engine non-crank can a BCM failure symptom (if security system faults are eliminated).
  • The customer may experience a condition where the vehicle horn may chirp momentarily upon attempting vehicle entry. This condition may be intermittent and most likely will occur when the customer is attempting to unlock the vehicle using either the door key or the remote keyless entry (RKE) FOB.

We offer an excellent repair and reliability rebuild service for defective BCMs (Rebuilding is essential to maintaining reliability in the long term). This service has to be on an own unit rebuild basis because vehicle identity and security functions are programmed into the BCM during pre-sales dealer preparation. Rebuilding your own unit avoids programming costs! (This is a hidden cost when you fit a new BCM).

Components within the BCM are CMOS technology which are extremely vulnerable to ESD (Electro Static Discharge) damage. Merely opening the BCM can cause multiple component failures and result in the BCM becoming unrepairable. Please, please resist the temptation to remove cover and poke around inside - it could cost you a new BCM.


Odometer mileage readings in some models are electronically stored in 2 locations on the vehicle - the instrument cluster and the BCM. System programming ensures that in the event of any mismatch between the 2 locations, the odometer will permanently display the highest mileage!!! Merely switching on the ignition with another BCM (with higher recorded mileage) connected can cause the odometer to permanently display the higher mileage. The system CANNOT be changed back to the lower recorded mileage by reversing this procedure.

BCMs are also matched to door lock codes. Please ensure (with dealer) lock set bar and EKA codes are written down before parting with your BCM for exchange. If you can't establish these codes, be ready to spend hundreds dollars on a new lock set if you change the BCM.


  • Climate Control unit digital display is dim, dark or intermittent. Controls function OK.
  • Climate Control unit digital display is dark. Controls do not work. May work when cold.
  • Dark Display or does opposite of what it should - causes Heat when its warm outside and cool when its cold outside.
  • Electronic Climate Control dim, intermittent or non-functional.
  • Heater or airconditioner doesn't respond
  • The display readout is dead
  • The display is intermittent
  • Heater is stuck on high
  • Fan is stuck on high
  • The outside temperature reading displayed in the overhead console can, in certain low speed driving situations, display an incorrect value

Nearly every electrical function in your vehicle is controlled by the BCM. Any problems associated with the BCM or its fuse box will result in malfunction of the vehicle's electrical systems. In order to properly diagnose an electrical problem in a vehicle with BCM, you must have a solid understanding of the interaction between the BCM and its electrical fuse box.

Symptoms of BCM Failure

  • Horn honks briefly upon entering the vehicle. While this may happen intermittently, it most often occurs when trying to unlock the automobile with the door key or the remote keyless entry fob.
  • Fuse failure codes even after the fuse box has been replaced
  • Inability to crank the engine (assuming security system faults have been ruled out)
  • Faulty operation of door locks, indicators, electric windows, headlights, fuel filler flap, or sunroof

In order to achieve long-term reliability, a malfunctioning BCM should be rebuilt. A BCM rebuild must be on an own-unit rebuild basis, because of the way in which the BCM is programmed prior to sale with respect to the vehicle's security and identity during dealer preparation. If you opt for a rebuild rather than a new BCM, you can avoid the costs associated with reprogramming. HICLASS Electronics technicians offer world-class reliability in all of our BCM rebuilds.

Note: because certain elements of the BCM are very sensitive to electrostatic discharge, even opening the BCM can cause it to be irreparably damaged and result in the failure of multiple vehicle components. We strongly discourage you from opening the cover of the BCM, because of the high likelihood of it rendering the entire unit inoperable.


Before you decide to try and replace or repair your vehicle's BCM, it is important to understand how your vehicle functions with respect to door lock codes and odometer mileage readings.

Door lock codes are matched to BCMs. Before you exchange your BCM, have your dealer write down your car's EKA codes and lock set bar. Without them, you will wind up paying hundreds of dollars for a new lock set after you put in the new BCM.

Odometer mileage readings are stored in both the BCM and the instrument cluster. Your vehicle is programmed to permanently display the higher of the two numbers in the event of a mismatch. For example, if you turn on the ignition while your vehicle is connected to a BCM with a mileage of 100,000 and the previous BCM had 50,000 miles, your odometer will default to 100,000. Reversing the process does NOT restore the lower mileage!

Symptoms of Climate Control Unit Failure

  • Fan and/or heater is stuck on high
  • Display readout is intermittent or dead
  • Air conditioner and/or heater is unresponsive to controls
  • Incorrect value displayed by outside temperature reading, particularly while driving at low speeds
  • Electronic Climate Control light is intermittent, dim, or not functioning at all
  • Digital display on Climate Control unit is dim or dark. Controls may or may not function.
  • Display does the opposite of controls: AC when it's cold outside and/or heat when it's hot outside