​DDEC IV 9308 vs. 9307

Fernando DeMoura
March 2018

A DDEC IV is a DDEC IV right? I used to think so, too.

A Detroit Diesel industrial DDEC IV 23519308 is one of the most versatile engine control systems ever made. The 9308 can be powered by both 12 volts and 24 volts and can fire up to eight injectors. With the right programming a 9308 can run a two stroke, a four stroke, be linked with another 9308 to run a 16-cylinder engine or even run a HK6E 14-liter Series 60 and control an EGR and variable geometry turbo. On the firewall side a 9308 can power a generator, a boat, or a large pusher RV. A 9308 can do many things but there is one thing that in my opinion it shouldn’t be used for…a truck.

The 23519307 is the automotive variation of the 23519308. The 9307 cannot tolerate being powered by 24 volts and cannot run more than 6 cylinders. The 9307 is cheaper and simpler than the 9308 but if you are running a DDEC IV on a truck the 9307 is the best choice.

Here’s why…Pictured in the photo of the true 9307 you’ll see a single circuit board adhered to the back of the ECM. This is a good location because if water or fuel gets inside a 9307 it will settle near the bottom of the box and in most cases cause little if any harm. The more complex 9308 DDEC IV has two circuit boards, one on the back and one on the bottom. When water gets inside a 9308 the water sits on top of the lower circuit board and when circuits are energized electro potential difference between the traces and the aluminum case cause electrolysis to occur. This causes these tiny copper traces to rapidly oxidize and turn into green soup.

So why would the designers of the 9308 DDEC IV build an ECM this way? The 9308 was designed for industrial engines that spend their lives in enclosed environments. Water intrusion is not an issue with these applications. Life on the road for a DDEC IV deteriorates the sealant that keeps the case watertight. The longer the DDEC is exposed the greater the chance water will get in.

Most trucks run an automotive 23519307 DDEC IV but I’ve recently seen more and more 9308s being used on trucks. This used to be something I’d only see with aftermarket reman DDECs. Retired industrial 9308s that ran in enclosed environments would be reprogrammed and used for automotive use. As a result, the life of these 9308s would on average be shorter than the life you would normally get out of a 9307 when installed on a truck.

More than one source as told me that some freightliner dealers are substituting in the 9308 when the 9307 should be used and not offering any warranty when damage occurs. The DDEC pictured is labeled as a 9307 when internally it is clearly a 9308. Just look at the lower circuit board. The owner of this DDEC said he brought this from a Freightliner dealer. If you are given a choice go for the 9307.

Written by Fernando DeMoura, Diesel Control Service LLC.


Phone 412-327-940