Using the tester, check for open or short (power supply-output short, GND-output short) in the harness between terminals of data link connector and power steering CM.
Connector & terminal
(B40) No. 14 — (B450) No. 7: (B40) No. 6 — (B450) No. 6:
Is harness normal?
Replace the power steering CM.
Repair or replace the harness.