Faulty 1-2 shift solenoid (internal open circuit or high resistance); Damaged wiring or chafed harness in the solenoid circuit (open circuit or short to voltage); Corroded, loose or contaminated connector at the solenoid or internal transmission harness; Contaminated or degraded transmission fluid affecting the solenoid or valve body; Low or incorrect system voltage from a weak battery or charging fault; Faulty transmission control module driver circuit; Internal valve body or solenoid pack fault, depending on the transmission fitted.

P1843

1-2 Shift Solenoid Circuit High Voltage.

Chevrolet
Powertrain
Manufacturer code
Medium severity

How this code is built

P: SystemPowertrain
1: Defined byThe manufacturer
8: AreaTransmission
43: FaultThe specific fault in that area

What it means

P1843 on a Chevrolet means the transmission control module has detected a voltage that is higher than expected in the 1-2 shift solenoid circuit. The module monitors the solenoid control circuit and sets the code when the voltage reads high when it should be low, or does not match the commanded state. This points to an electrical fault in the solenoid, its wiring or the control module, rather than a purely mechanical gearbox problem.

Symptoms

Gearbox warning light or check engine light on
Harsh, delayed or flared 1-2 upshift
Transmission stuck in one gear (limp mode) with no proper shifting
Incorrect gear selection or shift pattern, such as skipping first or second
Poor acceleration or higher engine revs at a given speed
Possible poor fuel economy

Possible causes

Faulty 1-2 shift solenoid (internal open circuit or high resistance)likely
Damaged wiring or chafed harness in the solenoid circuit (open circuit or short to voltage)likely
Corroded, loose or contaminated connector at the solenoid or internal transmission harnesslikely
Contaminated or degraded transmission fluid affecting the solenoid or valve bodypossible
Low or incorrect system voltage from a weak battery or charging faultpossible
Faulty transmission control module driver circuitrare
Internal valve body or solenoid pack fault, depending on the transmission fittedrare

How to diagnose

Read all stored codes and freeze frame data, noting speed, gear, temperature and voltage when the fault set, and check for other transmission or battery-related codes
Check battery condition and charging voltage, as low or unstable voltage can cause false circuit codes
Check the transmission fluid level, condition and smell, following the procedure for the specific gearbox
Inspect the external wiring and connectors between the transmission and control module for damage, corrosion, water ingress or pushed-out pins
Measure the solenoid resistance and compare it with the specification for the model and transmission
Check the control circuit for open circuits, shorts to voltage and good earth, using the wiring diagram for the vehicle
Use a scan tool to command the solenoid and watch for a response and the circuit state
Inspect the internal harness and connector inside the transmission if external checks pass, as access depends on the model

How to fix

Repair or replace damaged wiring and terminals in the solenoid circuit
Clean, secure or replace corroded or faulty connectors
Replace the 1-2 shift solenoid, or the solenoid pack, if the resistance or operation is out of specification
Service the transmission with the correct fluid and filter if contamination is found, and repair any underlying cause
Repair the battery or charging system if voltage is found to be low or unstable
Replace or repair the transmission control module only after the wiring and solenoid have been proven good

Can I keep driving?

Medium severity

The car may be driven carefully a short distance if it still shifts, but fix it soon as the gearbox may go into limp mode and continued use can cause extra wear. Avoid heavy loads or towing until it has been repaired.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.