P0783 3-4 Shift Malfunction
Description and meaning of DTC p0783
On vehicles with electronically controlled automatic transmissions, the 3-4 shift solenoid is responsible for actuating the hydraulic circuits to activate clutches or bands that change gears inside the automatic transmission. The shift solenoids are controlled by either a Transmission Control Module (TCM), or the Engine Control Unit / Powertrain Control Module (ECU / PCM). The control circuit may be power or ground side controlled depending on the application. Some vehicles self-test the circuit even when the gear is not in use, the 3-4 shift solenoid may be an on / off solenoid, or duty cycle controlled. The PCM or TCM looks for an inductive kick to determine if the solenoid is functioning properly even when not in use. This brief activation is too fast for the solenoid to actually cause a shift in the transmission. When the solenoid is activated and turned off, the magnetic field collapses sending a slightly higher voltage to the PCM which is used to determine if the solenoid is functioning properly. Note: This DTC is nearly identical to P0781, P0782, P0784, and P0829.
p0783 diagnostic trouble code symptoms
Symptoms of a P0783 DTC may include:Check engine light illuminated (Malfunction Indicator Lamp / MIL)Vehicle will not shift from 3rd to 4th gearThis condition may illuminate a check engine light and possibly shut down the transmission controls altogether resulting in a "failsafe" mode that will only allow one default gear depending on the vehicles state with all solenoids off.
DTC p0783 - possible causes
Potential causes of a P0783 code include:3-4 shift solenoid failureElectrical short to power - pinched wiresElectrical short to ground - pinched wiresOpen in power or ground circuit wiring - disconnected or loose connectionsTCM or PCM internal failure
How to fix OBD-II diagnostic trouble code p0783
Disconnect PCM or TCM wiring harness, depending on the application and using an electrical diagram as reference, check for excessive resistance or an open in the control circuit. Using a Digital Volt Ohm Meter (DVOM) set to the Ohms scale, check for resistance on the 3-4 solenoid power and ground sources to determine if there is an open circuit or excessive resistance in the 3-4 solenoid. Visually inspect for for any pinched, disconnected or loose wires on the harness connectors. Short to power: Disconnect battery positive cable and wiring harness connector at transmission and check for continuity using the DVOM between power source and solenoid circuit wiring in key on / engine off (KOEO) position as well as the key off position. Short to ground: Disconnect battery positive cable and wiring harness connector at transmission and check for continuity using the DVOM between 3-4 solenoid power source and a known good ground. TCM or PCM failure: Using an advanced scan tool capable of controlling solenoids, manually activate the 3-4 shift solenoid. It may be necessary to manually activate transmission control relay on some vehicles if power is not present at the transmission wiring harness connector. If a scan tool is not available, it will be necessary to monitor the 3-4 solenoid circuit to determine if the TCM or PCM is sending a power or ground signal to the 3-4 solenoid during vehicle operation.