A 2014 Jeep Cherokee entered the shop with this complaint: "loss of communication at times." The diagnosis began with a scan for DTCs for each node on all the networks, and fault codes existed only for communication faults.
Get caught up with all the details on this vehicle diagnostic case.
What would you recommend doing next, given the data bullet points in last month’s challenge?
- Replace the least expensive node first.
- Replace all nodes with stored DTCs.
- Inspect connector between PCM and CAN_C bus.
- Replace PCM because fault occurs during drive only.
For those of you who chose answer No. 3, congratulations! The noise shown on only one end of the bus media, or wiring (but not the other) proves that there is a fault pertaining to the wiring harness (the bus, itself). If the fault was present at both locations, a further process of elimination would be required.
Answer No. 1 is incorrect as it is rarely prudent practice to replace parts simply due to the cost. Although there are times when a fault is contained within one of several components and further pinpointed testing may not be possible, this would be the rare occasion when the least expensive component might be replaced first.
Answer No. 2 is incorrect as the node setting the DTC is almost never the cause of the communication issue. Most likely the node(s) setting the DTC are simply complaining about the existing communication issue.
Answer No. 4 holds no merit at all. There is almost no correlation in logic to replace a PCM simply because the vehicle is physically in motion. It’s best to seek further education about the vehicle’s configuration, and network diagnostics, in general if you felt this was the best answer. But that’s alright, there are many fantastic classes out there for network diagnostics.
So did you ace this test? More than 9 out of 10 Motor Age readers got this one right! Look for the quiz at the bottom of our next Data Doesn't Lie column to see if your diagnosis is on track.
