How is fault code P1842 fixed?

Measure the solenoid before deciding whether the fault is inside the unit. - Read all codes and the freeze frame, then check fluid level, colour and smell - Inspect the case connector for fluid, corrosion and terminal damage, and the external harness for chafe - Measure solenoid resistance at the case connector and compare with specification; a very low reading confirms a shorted winding - With the solenoid disconnected, test the control wire back to the module for a short to ground - Command the solenoid with the scan tool and watch for a current or state change - Drop the pan, inspect the internal harness and the solenoid, and check the pan magnet for debris - Replace the shift solenoid, repair any damaged internal harness, and verify the 1-2 shift on a road test

Transmission Transfer Case Differential Lock-Up Feedback Switch Circuit Failure

Jump to the fix

Severity

Medium

Can I keep driving?

Usually drivable, but get it diagnosed without delay.

First step

Measure the solenoid before deciding whether the fault is inside the unit.

PPowertrain
1Manufacturer-specific
8Powertrain (Other)
42Sequence number

What does it mean?

P1842 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: 1-2 Shift Solenoid Circuit Low Input (4T80-E) .

Symptoms

Check engine lamp on with a transmission warning
No 1-2 upshift, or the unit stuck in a single gear
Very harsh or slipping 1-2 change when it does occur
High engine speed at low road speed with the car reluctant to accelerate
Limp mode, higher fuel consumption and rising fluid temperature

Likely causes

Solenoid control wire shorted to ground inside the transmission where the internal harness passes the valve body
Solenoid winding shorted internally, often after overheating
Fluid intrusion into the case connector creating a leakage path to ground
External harness chafed between the case connector and the module
Debris jamming the solenoid so it draws excessive current
Poor module ground affecting the driver reference
Module output driver damaged by the solenoid short

How to fix it

Read all codes and the freeze frame, then check fluid level, colour and smell
Inspect the case connector for fluid, corrosion and terminal damage, and the external harness for chafe
Measure solenoid resistance at the case connector and compare with specification; a very low reading confirms a shorted winding
With the solenoid disconnected, test the control wire back to the module for a short to ground
Command the solenoid with the scan tool and watch for a current or state change
Drop the pan, inspect the internal harness and the solenoid, and check the pan magnet for debris
Replace the shift solenoid, repair any damaged internal harness, and verify the 1-2 shift on a road test

Codes From the Same System

All Fault Codes

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This information follows the generic OBD-II definition and does not replace a vehicle-specific diagnosis. The severity rating is rule-based; an authorised diagnostic reading is required for a definitive answer.