Cause
Worn engine or transmission mounts
Perished or collapsed mounts letting the powertrain move further than it should on its bearers. It reaches the diagnostic system through movement rather than through anything electrical, which is why it appears on sensor and position codes and is almost never suspected.
Excess movement breaks things that assume the engine stays put. A harness routed with a fixed length is stretched on load reversal, a connector is tugged at its terminals, and a position sensor mounted across the engine-to-body gap sees a shift that is real but not what it is measuring. The characteristic symptom is a fault that appears on gear engagement, hard acceleration or overrun — moments of torque reversal — and never at steady speed.
It is felt before it is measured. A thump on selecting drive or reverse, a shudder pulling away, or vibration at idle that changes when the transmission is put in gear. Watch the powertrain move with the brakes held and the transmission loaded — a mount that lets the engine lift visibly is the finding, and a collapsed hydraulic mount will often be leaking its fluid where it can be seen.
Typically a moderate job.
Codes this can cause (4)
Codes where this is a likely explanation first, rather than merely a possible one.
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