P102D is a weird code, reporting a higher-than-expected current flowing through the heater circuit during the OFF portion of the control pulse. (That's what makes it weird.) It shares the same troubleshooting steps with the other O₂ sensor heater codes, so you could check the resistance of the heater, the wiring continuity and so on. But the business of current flowing when the power transistor ought to be OFF might be harder to find a cause for outside the ECM itself.
