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| Glad to hear that things appear to be waking up. Ground switching isn't too uncommon with modern controllers. I believe it's something about the transistors used to switch things behaving better if they're sinking voltage instead of providing it.
Since this tractor uses active terminators there isn't any reliable resistance measurements you can make as the terminator uses digital circuitry instead of the resistors found in passive terminators. You can usually diagnose them by unplugging one at a time or swapping them with a known good one. The easiest one will be the ISO hitch connector (terminator is built into it), I think the other one is hidden in the left rear corner of the cab, but I can't tell you exactly where. On AGCO products I've seen two types, one being a 2x2" white pyramid and the other looking more akin to a plug cover with a 1x1" base. They'll have a power, ground and the two CAN wires; in some cases there may be another pair of ground and power wires, but I don't have the service manual I was using at hand to check. Unplug one at a time and measure the CAN voltages between each step. If you unplug one of them and the voltages narrow down closer to 2.5V each then you've found the culprit.
That said, since they both add up to 5 volts, I'd be willing to try getting the autosteer to talk before I began digging too deep. The reason I say this is that the way the CAN bus transmits data is by pulling one line (CAN Hi) up to around 3-3.5 volts and the other (CAN Lo) down to around 1.5-2 volts when it is trying to transmit data. When no data is transmitting, they idle around 2.5.
This is why most meters will never show exactly 2.5 volts on each line. The meter is attempting to average the voltage variances on the data lines when data is transmitting. Depending on how the meter averages those values, you can typically see anything from 2.6-2.9 volts on the CAN Hi wire and 2.1-2.4 volts on the CAN Lo wire. It's kind of infuriating to diagnose because you honestly need a scope to really figure out what is what. This is why I've been taught to add the two values (IE 2.3+2.7=5, 2.4+2.6=5, 2+3=5, etc) to determine if the CAN-Bus is good. Between using different meters and the rate and amount of data transmitting, you'll always get different voltages.
Edited by Maxzillian 5/3/2013 23:11
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MT Challenger,Help!!!!!
