What does it mean?
P1843 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: 1-2 Shift Solenoid Circuit High Input (4T80-E) .
Symptoms
- Check engine lamp on with a gearbox warning message
- The transmission will not perform the 1-2 shift and stays in its default gear
- Harsh engagement and a firm bump when pulling away
- Engine revving high at low speed with poor acceleration
- Limp mode, increased fuel use and reduced drivability
Likely causes
- Open circuit in the solenoid control or feed wire, commonly at the case connector
- Solenoid winding open internally after heat or vibration damage
- Corroded, spread or backed-out terminal adding high resistance to the circuit
- Internal harness broken or its connector not fully seated after a valve body repair
- Lost solenoid supply from a blown fuse, failed relay or corroded splice
- High resistance in the module ground path
- Module driver failing open
How to fix it
- Read the codes and freeze frame, and check the fluid level and condition
- Inspect the case connector for corrosion, backed-out pins and a loose locking tab
- Measure the solenoid resistance from the case connector; an infinite or very high value confirms an open winding
- Test continuity of the control and feed wires from the module connector to the case connector
- Verify the solenoid supply voltage and check the associated fuse and relay
- Drop the pan and inspect the internal harness and solenoid connector if the external side reads correctly
- Replace the solenoid or repair the circuit, then confirm the 1-2 shift occurs normally on a road test