2015 Kenworth

A 2015 Kenworth T660 PACCAR MX-13 had the concern of using a tank of diesel exhaust fluid every 1000 miles or so, which is far too much DEF. I remembered helping a shop out that replaced 3 doser valves in one year on a 2011 Volvo D13. Upon inspection, we found a large buildup of crystallized diesel exhaust fluid in the exhaust pipe less than six weeks after a dealer replaced the valve and cleaned the pipe. On that one, the exhaust temperature wasn’t hot enough to completely atomize the DEF. The DEF crystallizes, building up and restricting the exhaust pipe. Volvo’s repair is and insulated wrap around the pipe several inches from the doser valve, maintaining more heat. All Kenworth’s beginning with 2013 emission level engines utilize Selective Catalyst Reduction (SCR). SCR is a process in which Diesel Exhaust Fluid (DEF) is injected into the exhaust downstream of the engine. DEF is converted to ammonia by the heat of the exhaust system. Inside of the SCR canister a catalyst causes a chemical reaction to occur be­tween the ammonia and NOx, turning it into water and nitrogen.

On our Kenworth, we pulled the DEF composition pipe, cleaned the crystallization, and reinstalled the pipe. No DTCs were stored.

Next, we performed the system initiation verification cycle. You either drive the Kenworth with a loaded trailer or bobtail—but the coolant temperature has to reach 150ºF.

“That was easy,” Brighton said.

“We’re only just beginning,” I laughed. “We have to do the steady state verification cycle now.”

The manufacturer prefers to have you use a loaded trailer on a flat road with minimum gradient, but we didn’t have one. “That’s okay, Brighton—we can turn on the A/C and fan to generate a load. We drove the Kenworth above 50 mph, highest gear, with an rpm window of 1100 to 1500. We had to activate the cruise on a continuous distance of 3-5 miles, but idiot drivers prevented that from ever happening. They cut in front of us without using turn signals and then slowed down.

“Drivers down here never did know what that lever on the side of the steering column does,” Brighton said.

We drove the Kenworth in three different increments of 1-mile each, which also works. Using a scan tool, I monitored exhaust gas temps before and after the SCR and pump module. We also had to perform the SCR and DEF Doser cycle the same way as the steady state cycle.

“Now a DTC just set,” I said, noticing a P3915. The EAS-3 ECU flags the code when the NOx sensor heater can’t maintain its normal operating temperature. It was back to Brighton’s pole barn. We rechecked connections and wiring, and I crosschecked component parts against the electronic catalog.

“Someone put a 24-volt NOx sensor in place of the 12-volt sensor,” I said, noticing the wiring job.

“This truck was at the dealer a few times,” Brighton said.

We also checked the resistance of the A-CAN nework at the NOx sensor after the converter (60 Ω measured),the terminators in the PCI ECM (122 Ω measured). By unplugging the Aftertreatment harness connector from the engine harness connector, you can isolate the E-CAN from the A-CAN network. There is an A-CAN terminator in the PCI ECM and one in the EAS-3 ECU connector. The individual terminators came in at 120 Ω, which was good.

A road test and steady state verification cycle confirmed the repair. We later discovered that the original truck owner was a backyard mechanic and installed the wrong NOx sensor.

“This driver also uses a Georgia Overdrive—what is that?” Brighton asked.