Engine code p1780 - 2002 Saturn L-Series

DTC P1780
Circuit Description
This DTC indicates that the engine control module (ECM) received a message from the transmission control module (TCM) to turn ON the MIL (SERVICE ENGINE SOON) telltale due to a transmission related OBD II failure. The ECM will send a message via the controller area network (CAN) link to the body control module (BCM), which will send a message over the class 2 link to the instrument panel (I/P) cluster to turn ON the MIL.
Conditions for Setting the DTC
DTC P1780 will set if the ECM received a MIL request message from the TCM over the CAN link.
DTC P1780 is a type B DTC.
Diagnostic Aids
DTC P1780 does not indicate a fault with the CAN link circuit.
DTC P1780 does not indicate a fault with the ECM.
Diagnose any TCM related DTCs first.


You need a scan tool that can read transmission control module codes .

Gary, Depends on year, make and model. Transmission code P1780 - Trans Control Switch (O/D Cancel) Out of Self Test Range,Pressure switch circuit, Park/Neutral Position [PNP] Switch Circuit, see other reasons in the links below.
If no drive ability issues, erase code and see if it comes back. If code returns have a good tech. diagnose and estimate repair. Check the attached links,instruction and guides, Good luck
"I hope this helped you out, if so let me know by pressing the helpful button. Check out some of my other posts if you need more tips and info
P1780 Trans Control Switch Cancel Out of Self Test Range
https://answers.yahoo.com/question/index?qid=20070720121948AATjvTw
http://www.aboutautomobile.com/DTC/P1780

DTC P1780 (3.0L (L81))

To improve shift feel, the transmission control module (TCM) may request that the engine control module (ECM) reduce engine torque during shift events. When such a request is received, the ECM responds by retarding the base ignition timing and notifying the TCM that the request has succeeded. If the ECM is unable to comply with the request, the ECM sends the TCM a message that the request has failed.
The torque reduction request is sent to the ECM through a communication network called the controller area network (CAN). Two circuits are used to communicate CAN data between the ECM and TCM. A fault in the CAN will not cause DTC P1780 to set by itself. If a CAN fault occurs, other DTCs will set before DTC P1780.
When the TCM receives a torque reduction failure message from the ECM, then DTC P1780 will set. DTC P1780 is a type C DTC. Take your pick of which you think this code is for , this or the TSB - technical service bulletin. What need to hook up scan tool an data PID'S - Do you know what PID'S are ? sensor data read on a scan tool .

we need the vehicle make ,year and engine size to verify exactly what the codes refer to
Add the extra codes as some codes cross reference and give a common fault

P1780 Park/Neutral Postion (PNP) Switch Circuit Engine Torque Signal Circuit

The codes need to reset with a diagnostic plug in device that may only be located at a dealers service center.

p1780 FORD Code
Transmission Control Switch circuit is out of Self-Test Range
If it is a different vehicle go to google and type OBD2 codes and pick your manufacturer then pick vehicle or just scroll the p codes

P1780 Is the indication that the neutral safety switch has failed. It is mounted on the side of the transmission where the linkage is attached. replacement is the normal fix. This part is a bit pricey and you might get lucky looking in a salvage yard for a used one.

P1780 is a bad neutral/park (mode) switch. This is not a common problem but I have seen them bad.The switch is located on top of the transmission where the linkage that the shift cable connects.If you ment code P1870 the let me know because this is much more common and I will go through that explanation.

Yes the P1780 DTC is the Transmission Control Switch Circuit is out of self test range.