A shift solenoid is a plunger-like device that channels pressurized hydraulic fluid/ATF in order to actuate a gear change. If your vehicle has a P1842 DTC, then the solenoid responsible for the shift from 1st to 2nd gear is experiencing a low voltage condition, which typically indicates a short circuit.
How Serious is the Code?
A P1842 diagnostic trouble code is extremely serious, because it means your transmission cannot change gears the way was designed to. Needless to say, you will start experiencing drivability issues. Followed shortly by a broken transmission.
Symptoms of a P1842 include:
- Harsh shifts
- Delayed shifts
- Vehicle will not move
- Limp mode
- Overheated transmission
- Low transmission fluid level
- Dirty transmission fluid
- Clogged hydraulic passages
- Damaged or corroded wiring/connectors
- Failed 1-2 shift solenoid
- Failed transmission pump
How to Diagnose the Code?
When diagnosing a P1842 OBDII diagnostic trouble code, it’s important to pay attention to the condition of the transmission fluid. Dirty fluid, a dirty transmission filter, and metal shavings can all prevent the 1-2 shift solenoid from working properly. If no problems are found in the ATF, then the wiring and connectors on the transmission wiring harness carefully inspected for signs of a short or corrosion. If no problems are found here, then the 1-2 solenoid, transmission pump and valve body should be tested.
Common Mistakes When Diagnosing
It’s not uncommon for most mechanics to suspect that a P1842 DTC automatically means that the 1-2 solenoid has failed. When many times, could just be dirty transmission fluid or a wiring issue.
What Repairs Will Fix P1842?
- Changing the transmission fluid/filter
- Repair or replace damaged wiring/connectors
- Replace the 1-2 shift solenoid
- Repair or replace the transmission pump
- Repair or replace the valve body
P1843 – 1-2 Shift Solenoid High Voltage