P07BD — Transmission Park Position Sensor/Switch B Circuit Intermittent/Erratic

P07BD is stored when the ECU sees intermittent fault on transmission. That describes how the circuit is behaving, not which part has failed — the wiring, the connector and the component itself can all produce it, which is why the checks below start with the cheapest.

Common causes

The cause is almost always one of a few things. Here they are — P07BD rarely comes from anything outside this list:

• Connector that loses contact with vibration or temperature
• Wire broken inside its insulation, making contact only sometimes
• Corrosion that conducts until it gets wet or hot
• Component failing only under load or at temperature

Where to start

In the order a sensible mechanic would work — the cheap checks first, the expensive replacements only after:

1. Wiggle-test the loom and connector with live data on screen — the fault has to be caught while it is happening
2. Check freeze-frame data for the conditions that trigger it (temperature, load, speed)
3. Inspect connectors for spread terminals and green corrosion
4. Where possible, monitor the circuit over a drive rather than at idle
5. Replace only the part you have actually seen misbehave

That is what holds for P07BD in general. From here it depends on your engine — tell me which car it is and what it does, and I will give you the steps for it: real procedures, torque figures and diagrams instead of general advice.