Western Star

The 2012 Western Star 4900 Series with a Detroit Diesel Series 60 originally had a SPN 524/FMI 9 DTC stored, indicating a J1939 ETC2 Message Missing. The technicians working on this truck checked for proper CPC configuration, ultimately replacing the CPC, because it failed to download MCM static fault data. After that, an SPN 630/FMI 14 Code flagged.

This code indicated that the CPC failed to download MCM static fault data and the repair is to reprogram the CPC with the latest software release. “After we did that, we ended up with an inconsistent static fault code data, reported by the MCM,” a very frustrated Dave Gordon, the technician, said. “I reprogrammed the MCM with the latest software,” he said. It was after that, the SPN 625 FMI 9 code set—abnormal data update rate.

When I got to the shop, it was in a pole barn, well-equipped and well-lit. I performed all the basic checks: battery connections and battery state of charge; fuses, grounds—I found a bad ground at the CPC. Once we eliminated the bad ground, I took out my ancient AM pocket radio. The shop was filled with interference. I once found interference coming from the rain gutters of an old barn. The farmer used a ladder to get up to the loft, and when he grabbed the rain gutter for support, he screamed from an electric shock. The interference on my AM radio stopped. He came down the ladder, still shaking, and asked me if it could be connected to a problem he was having when touching the metal sink in the barn or the refrigerator. It was.

Getting back to the pole barn/truck shop: Electromagnetic Interference is caused by one device inducing voltage (generating a discrete voltage without a direct electrical connection) within a second component.  Induced voltage occurs when devices are not properly shielded, are laid out improperly (e.g. coiled around objects or run parallel for the entire distance), use high frequency AC voltage, or are grounded improperly.

His shop lights used electronic ballasts.  Because ballasts typically generate a humming or buzzing noise – electronic ballasts are quieter than traditional magnetic ballasts, but the hum still exists – remotely mounted ballasts are sometimes preferred, which is what Allman had in his shop. Remotely installed electronic ballasts generate substantial amounts of EMI due to their higher operating frequencies (magnetic ballasts operate at 60 Hz while electronic ballasts are typically operated at 20-60 KHz, that’s 50 to 200 times greater). 

 If the connection cables are unshielded, the high frequency will convert the cables into a powerful antenna, creating an electromagnetic field that can affect radios, Wi-Fi connections, and cell signals.  In a fluorescent system, the fluorescent lamp itself is capable of radiating electromagnetic waves at frequencies of 10 KHz to 100 MHz depending on the electronic ballast connected to it.

Allman’s top technician, Dave, was attempting to program the truck’s ECU’s in the presence of all that EMI.

“So, how can you eliminate EMI?” Allman asked.

“Ensuring proper ground connections for all electrical devices will shunt high frequency interference to an earth ground or common, for starters,” I said.  If grounding is not done properly, cables, grounds, or electrical equipment can act as a very powerful antenna, radiating out a strong EM field.  “Grounding the fixture and ballast to a common earth ground will help prevent this from occurring.”

“We do a lot of programming,” Dave said.

“Cable runs should be placed in metal conduits, and fluorescent or HID lights can be housed in luminaires with copper mesh or conductive glass to shield against EMI generated by the cables or lamps.”

I also mentioned that all exposed conductors should be shielded.  The conductive material of the shielding will absorb the EM field and prevent radiated or conducted EMI.

Allman vowed to get the EMI down to manageable levels in his shop. With the Western Star’s ECUs properly programmed (without interference), the problems were resolved.