Low Voltage, Intermittent Communication, No Regeneration - $1,200 EGR Valve?
A case study of diagnostic strategy and working with what you have. Doesn't make the make, model, or product line (on road or off).
John Deere 244K-II (FT4) - 1LU244KTVZB046717 w/ Yanmar 4TNV98CT engine.
Before we delve into the laundry list of codes, let me give you a little info here. 244K-II is a machine made for John Deere by Liebherr and equipped with a Yanmar engine. So we have a few different languages going on here; it can make it interesting at times.
Codes & Brief Description (the description is pretty much all I get in the service information - code set parameter documentation is almost non-existent):
- P068A - ECU Main Relay Early Opening (main relay is internal to the ECU) (*turning battery disconnect off with machine running will cause this)
- P1424 - DPF OP Interface Back-Up Mode
- P1421 - Stationary Regeneration Standby
- P2459 - Regen Defect (Stationary Regen Not Performed)
- U1303 - Y_DPFIF CAN Message Reception Timeout
- … - CCU Improper Shutdown
- … - CAN 1 Abnormal Update Rate
- … - CAN 2 Abnormal Update Rate
- … - CCU Operating Hours Not Saved
- … - Battery Voltage Low - Engine Running
- … - CCU EEPROM Error
This case study starts out, as most of mine do, with a phone call from a road technician. Customer had called in requested a forced service regeneration because machine had de-rated and was essentially useless for loading salt. Fairly common occurrence for operators to short trip machines like this or inhibit regeneration due to lack of understanding of how to properly run the machine. Technician hooked up Service Advisor to the machine and was getting ready to start regeneration when he noticed a laundry list of codes popping up, a red STOP Engine light, and an incredibly annoying beep (all designed to force an operator to stop, sadly it's rarely enough).
JD is pretty convenient with certain machines, they have a test called DTC Priority test. It takes a list of codes such as this one and cross-references them. It then gives you a code to begin with and filters down so that your focused on direct faults instead of a fault code caused by another fault code. This machine was not one of them, and you'll notice that they aren't labeled in the DTC list, that means manual look-up. I recognized the … (battery voltage low - engine running), so I had the tech check out the belt drive, charging system, and battery while I pulled up the descriptions. The engine load profile was also brought up at this time as the initial complaint was regeneration related.
As you can see this machine has spent the vast majority of it's life idling with little to no load on it. That is a big no-no on these new engines with DOC/DPF and SCR (selective catalytic reduction). I get a call back from the tech at this point, alternator drive belt was loose and battery voltage was down to 11.5V with the engine running. He tightened the belt, cleared the codes (we both agreed that codes relating directly or indirectly to low voltage would likely not re-occur). Low voltage codes would be our … (low battery voltage), this caused our P068A (main relay opening early due to low voltage) which in turn caused our … (improper shutdown as it has a cycle down time after key off to store all its data), … (EEPROM error) and … (CCU operating hours not saved). The CCU (chassis control unit) is fed 5V from the ECU and remains powered up after the key is switched off to save data. If it loses power (due to the ECU losing power) it will throw all sorts of codes.
After charging the battery up I had the tech perform a Tuple Error Correction test (internal computer memory correction essentially), reprogram of the CCU with the updated Liebherr software, and finally a Chassis Configuration Test (this ensures that the CCU is operational and correctly configured for the specific machine). The only codes that re-occurred were our regeneration defect codes, our U1303, and our CAN abnormal update rate codes. Watching some live data recordings from the tech didn't bring anything to my attention, so I packed up some equipment and headed out to meet.
I knew from the theory of operation that the exhaust after-treatment system is on it's own leg of the CANbus (CAN 1). I hadn't seen any data to suggest that any components weren't working so I pulled a schematic and found CAN 1 only runs to the EGR valve. The EGR valve has power, ground, CAN H, CAN L wires. Nothing else on that leg. Bi-directional control of the EGR valve was attempted but unsuccessful (I believed at the time that this was due to the regen codes locking out some of the controls as a failsafe, because EGR is commanded fully closed to perform regeneration). I was able to initiate a service regeneration and this gave me a solid 2 hours to think about my direction and the system. I decided that we would attempt bi-directional controls again (they failed).
Seeing no other real direction, and wanting to get rid of communication errors before chasing anything else, I brought out the scope. Watching the CAN data, back-probed at the EGR valve, I didn't see anything out of the ordinary. I attempted bi-directional control once more while monitoring the CAN data and I saw this waveform. I am no network communication expert but I didn't like how it looked, and I also didn't like how I had no control over the valve. So I unplugged the valve and immediately the signal went back to a "standard" CAN signal. Plugging the valve back in caused the signal to continue to degrade. I unplugged the valve once again after this and continued on.
I cleared all codes and the only one that re-occurred was U1303 - CAN message timeout. Feeling 90% confident I next-day aired a new EGR valve and gaskets in. Made the repair and scoped the signal again. It was exactly what I expected to see.
So a confirmed issue where a CANbus EGR valve was able to scramble the network enough to cause communication errors. Definitely a first for me. Those more adept at interpreting network waveforms may be able to confirm or deny how much difference that network signal has. I know I replaced the EGR valve, loaded salt spreaders with the machine for about an hour and had no fault re-occurrences. I now also had bi-directional control of the EGR valve, as well as proper computer controlled operation while running.
Final verification was putting the machine into regeneration from the operator's seat, it went in and passed perfectly. Full repair verification complete.
Lesson here is that even when faced with a scary amount of codes there is no need to get nervous. In fact it is just more data pointing you to the right direction. The more strange the failure is, the easier it can be to track down. How many more variables are there to a simple low power complaint with no codes compared to a list of 13 codes all pointing in a general direction? By studying theory of operation and using logic we were able to knock out a lot of codes just by grouping them and tightening a loose belt. Then we were able to track down to one specific component based off a schematic. Using some network and tooling knowledge we were able to get to a relatively confident diagnosis and then confirm as best as we could given the lack of concrete SI.
I promise one day I will post a nice short 1 paragraph tech tip. Thanks to everyone who trudges through these write-ups and I hope they are at useful in some way, shape or form.