​DDEC and Caterpillar internal ECM Batteries

Fernando DeMoura
June 2016

If you have a Cummins, you don’t have to worry about an internal ECM battery. Caterpillar ECMs started using internal batteries around 1993 with the A2 (40 pin) model. Detroit Diesel started using them in 1998 with the DDEC IV. The internal batteries were needed to take advantage of newer memory technology and for tracking the date and time. This newer memory needed a constant supply of electricity to hold saved information. What happens when you unplug an alarm clock? You're stuck resetting the time and alarm settings. The same thing happens when you unplug your DDEC IV from your truck while it has a dead internal battery. It resets the time and loses some programmable settings.

Cummins has been making due without internal ECM batteries so why do technicians make a say an ECM is junk when the battery dies? Well, when a truck doesn’t start someone is eventually going to check for diagnostic codes. If it’s an updated DDEC IV and it shows an “RTC backup battery low” code the technician associates that with the reason the ECM isn’t starting the truck. He is actually seeing a symptom of another problem not the cause. The problem can start with the battery but not because the battery failed to provide voltage but like most dead batteries when they get old enough they start to leak acid. In this case the reason the ECM isn’t starting the truck is because acid leaking out of the battery caused damage.

A low internal battery voltage can also be a sign that water or oil got in and is shorting out the battery. Sometimes it’s not water causing the short but an internal component failure. If the truck runs fine and the only symptom is this code then the battery might have just died of natural causes. It’s impossible to tell what the cause of this code is without opening up the case but don’t assume the ECM is junk. If you have a Caterpillar ECM that shows the diagnostic code “timing calibration not performed” even after you do the timing calibration procedure or load the timing calibration data your internal battery may have failed. The memory that holds this part of the program needs voltage to store data. Unless you are seeing this problem with a Caterpillar ECM then don’t worry about the battery. The battery life in Caterpillar ECMs is extremely long. I have seen one that was over 20 years old that still had life left in it. All of these batteries are should run at least 10 years. If an ECM is less than 10 years old and has low internal battery voltage expect to find something defective or something shorted. If you’re not having any of these problems and you’re internal battery voltage is above 2 volts then the best way to take care of your internal ECM battery is to keep your ECM connected to your truck and keep your truck batteries charged.

Written by Fernando DeMoura, Diesel Control Service. Website: Dieselcontrolservice.com. Phone 412-327-9400