When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
So if you have experience troubleshooting equipment, I’m sure you’ll get along ok figuring this out. Below is a wiring diagram, shift schedule, and diagnostic flow chart for the VSS. Here’s how I would approach it:
1) Start with basic inspection of wiring harness, looking for damaged or chafed areas, unplug all the connectors on the transmission and transfer case to inspect for corrosion and loose terminals. This would also include inspection of the harness at the PCM (behind glove box). Repair/clean as needed.
2) Key on, engine off, verify battery voltage to pin E (pink wire from trans fuse) of the transmission connector (right rear of transmission).
3) Once the general condition of the wiring has been verified, Disconnect the PCM (unhook negative battery cables first) and perform continuity checks on each of the solenoid control circuits. I don’t know exactly what you should see (data is buried on service info, if it’s there at all), but if you check the resistance of each circuit relative to the others, that MIGHT indicate a problem with one of the solenoids. The readings will have to be interpreted accordingly, and I’ll keep trying to find some actual numbers in the mean time.
Also, note that the PCM is controlling the solenoids from the ground side only - you’ll have to run a jumper to either the trans fuse or the transmission to check the complete circuit of each solenoid.
4) Note that the flow chart states to test the VSS with the drive wheels off the ground - I wouldn’t do it that way for the simple reason that you know the hard shifts are happening under load - if the wheels are off the ground, it may not shift harshly at all and that could affect your test results. Since the PCM is located in the cabin, it shouldn’t be at all difficult to set up your meter to monitor the VSS signal ckt as you’re driving by back probing the PCM connector.
5) While driving to monitor the VSS signal, also note the shift points and see if they correspond to the chart.
So if you have experience troubleshooting equipment, I’m sure you’ll get along ok figuring this out. Below is a wiring diagram, shift schedule, and diagnostic flow chart for the VSS. Here’s how I would approach it:
1) Start with basic inspection of wiring harness, looking for damaged or chafed areas, unplug all the connectors on the transmission and transfer case to inspect for corrosion and loose terminals. This would also include inspection of the harness at the PCM (behind glove box). Repair/clean as needed.
2) Key on, engine off, verify battery voltage to pin E (pink wire from trans fuse) of the transmission connector (right rear of transmission).
3) Once the general condition of the wiring has been verified, Disconnect the PCM (unhook negative battery cables first) and perform continuity checks on each of the solenoid control circuits. I don’t know exactly what you should see (data is buried on service info, if it’s there at all), but if you check the resistance of each circuit relative to the others, that MIGHT indicate a problem with one of the solenoids. The readings will have to be interpreted accordingly, and I’ll keep trying to find some actual numbers in the mean time.
Also, note that the PCM is controlling the solenoids from the ground side only - you’ll have to run a jumper to either the trans fuse or the transmission to check the complete circuit of each solenoid.
4) Note that the flow chart states to test the VSS with the drive wheels off the ground - I wouldn’t do it that way for the simple reason that you know the hard shifts are happening under load - if the wheels are off the ground, it may not shift harshly at all and that could affect your test results. Since the PCM is located in the cabin, it shouldn’t be at all difficult to set up your meter to monitor the VSS signal ckt as you’re driving by back probing the PCM connector.
5) While driving to monitor the VSS signal, also note the shift points and see if they correspond to the chart.
Hopefully this is enough to get it figured out.
Hi Gumby22 and Big Thanks!
I really appreciate your help. Next two weeks I'm on holiday, building up the house (I'm not allowed to repair my truck, says my wife)
I'll let you know what I find after my holiday.
K2500 6.2 D 1993 4x4 with 4160 tranny shifting rough
Originally Posted by Gumby22
So if you have experience troubleshooting equipment, I’m sure you’ll get along ok figuring this out. Below is a wiring diagram, shift schedule, and diagnostic flow chart for the VSS. Here’s how I would approach it:
1) Start with basic inspection of wiring harness, looking for damaged or chafed areas, unplug all the connectors on the transmission and transfer case to inspect for corrosion and loose terminals. This would also include inspection of the harness at the PCM (behind glove box). Repair/clean as needed.
2) Key on, engine off, verify battery voltage to pin E (pink wire from trans fuse) of the transmission connector (right rear of transmission).
3) Once the general condition of the wiring has been verified, Disconnect the PCM (unhook negative battery cables first) and perform continuity checks on each of the solenoid control circuits. I don’t know exactly what you should see (data is buried on service info, if it’s there at all), but if you check the resistance of each circuit relative to the others, that MIGHT indicate a problem with one of the solenoids. The readings will have to be interpreted accordingly, and I’ll keep trying to find some actual numbers in the mean time.
Also, note that the PCM is controlling the solenoids from the ground side only - you’ll have to run a jumper to either the trans fuse or the transmission to check the complete circuit of each solenoid.
4) Note that the flow chart states to test the VSS with the drive wheels off the ground - I wouldn’t do it that way for the simple reason that you know the hard shifts are happening under load - if the wheels are off the ground, it may not shift harshly at all and that could affect your test results. Since the PCM is located in the cabin, it shouldn’t be at all difficult to set up your meter to monitor the VSS signal ckt as you’re driving by back probing the PCM connector.
5) While driving to monitor the VSS signal, also note the shift points and see if they correspond to the chart.
Hopefully this is enough to get it figured out.
Hi Gumby 22
just to let you know. Shifting is smooth like normal now. I changed the oil to GM. Also filter.
It is also possible to have inadequate line pressure due to a leaking boost valve, clogged EPC filter screen, failing EPC solenoid, or possibly leaky seals throughout the transmission
July 21st, 2020, 8:26 PM
