What does it mean?
P1788 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: A/T ATSDLA Signal Circuit Malfunction .
Symptoms
- MIL (check engine lamp) is on and further transmission codes are usually present
- The function that the output controls does not work, or works only intermittently
- Transmission behaviour becomes unpredictable, with harsh or mistimed shifts
- Limp mode with a fixed gear on some vehicles
- An indicator that this circuit drives may fail to light or may stay lit
- The fault often returns immediately after being cleared
Likely causes
- Open circuit in the output wire between the module and the device it drives
- Short to ground on the output line, often where the loom runs behind the dash or along the body
- Short to battery voltage holding the output permanently active
- Failed device on the end of the circuit, drawing too much or no current at all
- Corroded connector or a backed-out terminal at either end
- Blown fuse or a lost supply feed to the driven device
- Failed output driver stage inside the control module
How to fix it
- Read all codes and note which other transmission faults are stored
- Command the output with a bi-directional scan tool and verify the device responds
- Measure the resistance of the driven device and check it for a short to ground
- With everything disconnected, check the output wire for continuity and for shorts to ground and battery
- Verify the supply fuse and feed to the driven device with the ignition on
- Repair the wiring or replace the device; consider the control module only once the circuit has been fully proven