Hello All,
I had a similar experience with my mom's 2000 Camry LE. 3.0L V6 with 131,000 miles, automatic transmission. The symptoms were as follows:
1. Check Engine was lit on the dashboard panel. ODBII code of P1780.
2. The R (reverse light) on the dashboard would light up each time you hit the brake and go away when you released the pedal (in all gears except Park or Reverse).
3. Dashboard panel also had a lit symbol of the vehicle that indicated that something was wrong with the rear lights (the symbol actually did not appear until you press on the brakes after starting the car each time and stayed on until you turned off the car). The rear lights were functioning properly.
4. Whenever you brake after driving at least 30 MPH, the car would shudder just before coming to a full stop.
Had all the brake pads changed on all 4 wheels just 4 days before this all started. Took the car back to the mechanic who found the same code of P1780. He stated that the problem was with the tranny. He said two valves were stuck open and that they caused this code. Report from mechanic said that the tranny fluid was burnt and needed to be flushed and replaced.
I did some research myself and found this forum and your guys post. This led me into the right direction. My brother is a smog technician and together we checked the wiring harness in the trunk but did not find any frayed wires. We then physically inspected the rear brake bulbs (remember that they were functioning properly). On the passenger side bulb, we noticed a black hue to the bulb similar to how a burned out bulb looks.
On a whim, we swapped out this bulb and voila, the check engine light disappeared. I turned off the engine and restarted the car and the symbol for a problem with the rear lights did not come on when I pressed on the brake pedal and the check engine remained off.
We took the car for a drive and the shudder was gone. My brother summized that the bulb was causing the P1780 code perhaps because of a drop in resistance and the ECM interpretted this incorrectly.
So thank you all for posting. I hope that this helps someone else with this issue.