Tractor Manager and/or Electric Steer Manager is
intermittent.

Before checking all this, test for shorts to frame. Check static strap and use ohmeter to verify 10,000 ohm resister in static starp standoff is still intact. just put one lead on end of strap, other to frame. there should be 10K ohms. You can replace just the resister if it's blown.
Check main contacter points, battery state of charge. Grab harness while steering left and right, check for loose conections. Check drive unit radial rings for excess wear. 120 thou maximun play.

Communication Error Code Troubleshooting

Communication Error
Code Troubleshooting
Intermittent Communication
Codes
If possible, determine what the operator was
doing when the codes were generated; driving,
plugging, lifting, sounding horn, and so on.
Focus on these circuits for shorts to frame and
external noise being generated which can
interfere with the communication circuits.
Determine where in the SelfTest Cycle the code
is generated (for instance, when the drive motor
is energized or when the horn was sounded).
During SelfTest
Make sure the key switch is turned OFF for at
least 5 seconds before turning it back on. Test
the key switch for high resistance. If nothing is
found in the following steps replace the key
switch.
Inspect the termination jumpers on the cards
as follows:
* Tractor Manager: E1 Jumper IN without
Electronic Steering; OUT with Electronic
Steering. See Figure 5-12.
* Carriage Control Card: E3 jumper IN
without SMARTi; OUT with SMARTi. See
Figure 5-13.
* Electronic Steer Manager: E1 jumper IN on
all trucks. See Figure 5-14
Test for shorts to frame. See Shorts to Frame
Test on page 5-8.
If equipped with optional light/fan package,
disconnect PC5. If code goes away, troubleshoot
light/fan circuitry.
NOTE: The condition of the light/fan
suppressor module cannot be checked
with a DMM. If the suppressor module is
suspected to be bad, replace it.
you will need wiring manual!

Good luck!