Truck going into "Limp mode"

[Ken K]

Yea, plows suck the juice fast, I have two alternators and two batteries in mine and its still struggles at times when I have the radio blasting and headlights on plowing short runs when I need to change plow direction often.

To RichLo, Retired ASE Master Tech with some ideas. Check the output from each alternator to verify proper operation. Running two batteries is fine with good connections, good batteries, but more so remember the alternators run all accessories once started as the batteries only start the engine. Voltage drop while running your snow plow up or down is the quickest most accurate check the integrity of connections and relays. On high current circuits, expect to see 0.50 volts lost across a connection or relay contacts, same with B+ from alternator to battery(s). With current flowing (Circuit on), use your DMM across any single path the current takes in a series circuit. Red led / black led, who cares, same reading, just with a (-) symbol on DMM. Test each wire, across each connection, across each relay and same with ground. You will find the loss of voltage that causes you systems issue. More often than not, I found bad grounds. I clean, add more / new, use dielectric grease and star washer and make sure the size of the wire, matches the amount of current for the length of wire you have. Best of luck.

 

[Ken K]

P0785 Shift Solenoid
I replaced those- didn't fix it.
Went back in a second time and replaced all the electronics and wire harness in the pan, replaced throttle position sensor- didn't fix it.
It will run perfectly when I first crank up, for a couple of miles to the first corner I make and when it shifts from there, it slams into second, dash light come on and limp mode the rest of the trip.
I had a brand new battery but it was bad and crapping out when this started, but only realized the battery was bad after I replaced everything. I thought maybe it was a voltage problem, but I have since replaced battery and cables and had the alternator checked out, but the problem is still there. I erase the codes, but every time I get that hard shift, the same code pops up again.

Retired ASE Master tech, Double check to make sure the speedo or cruise control does not drop out. It the tranny's speed sensor has three wires, it is a "Hall-Effect" type. It produces an on-off signal that is shared to the Speedo (IP), BCM for cruise control and the PCM for shift points. At this point, slide the speed signal device out of trans and check the condition of the plastic driven gear for "Apple Coring". This concaved wear pattern will cause loss of speed signal and other strange "Speed" related problems. Remember, it's color coded for the number of teeth for speed correction for final drive or tire size change. But, as other post have mentioned, having a good battery, grounds and connections is a good place to start. Best of luck.

 

[Jeff Davis]

Retired ASE Master tech, Double check to make sure the speedo or cruise control does not drop out. It the tranny's speed sensor has three wires, it is a "Hall-Effect" type. It produces an on-off signal that is shared to the Speedo (IP), BCM for cruise control and the PCM for shift points. At this point, slide the speed signal device out of trans and check the condition of the plastic driven gear for "Apple Coring". This concaved wear pattern will cause loss of speed signal and other strange "Speed" related problems. Remember, it's color coded for the number of teeth for speed correction for final drive or tire size change. But, as other post have mentioned, having a good battery, grounds and connections is a good place to start. Best of luck.

Is this for my scenario or for the snow plow problem?