Faulty 1-2 shift solenoid with an open internal winding; Damaged, chafed or corroded wiring between the solenoid and the control module, including the internal transmission harness; Poor connection or corrosion at the transmission electrical connector or control module connector; Wiring short to a voltage source; Transmission fluid contamination or debris affecting the solenoid and connector inside the valve body; Faulty transmission control module driver circuit, or the control function in the engine control module on integrated systems (depends on model and transmission).

P1843

1-2 Shift Solenoid Circuit High Voltage.

Buick
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 Buick means the transmission control module has detected a high voltage on the 1-2 shift solenoid circuit. The module expected the circuit voltage to be within a normal range when the solenoid was commanded on or off, but saw a higher voltage than it should, which points to an open circuit, a short to voltage or a faulty solenoid or driver.

Symptoms

Transmission warning light or check engine light on
Harsh, delayed or flared shifts between first and second gear
Transmission stuck in one gear or in a limp-home mode
Poor acceleration or higher fuel consumption
Gear selection that feels wrong or no 1-2 upshift

Possible causes

Faulty 1-2 shift solenoid with an open internal windinglikely
Damaged, chafed or corroded wiring between the solenoid and the control module, including the internal transmission harnesslikely
Poor connection or corrosion at the transmission electrical connector or control module connectorlikely
Wiring short to a voltage sourcepossible
Transmission fluid contamination or debris affecting the solenoid and connector inside the valve bodypossible
Faulty transmission control module driver circuit, or the control function in the engine control module on integrated systems (depends on model and transmission)rare

How to diagnose

Read all stored and pending codes and note the freeze frame data, including vehicle speed, gear and battery voltage
Check the transmission fluid level, condition and smell, looking for burnt fluid or metal debris
Inspect the external wiring and the transmission connector for damage, chafing, water ingress, bent pins and corrosion
Check the battery and charging voltage, as low or unstable voltage can upset circuit readings
Measure the 1-2 shift solenoid resistance at the connector and compare it with the specification for that model and transmission
Check the wiring for continuity, short to voltage and short to earth between the solenoid connector and the control module, following the wiring diagram
Command the solenoid with a suitable scan tool and watch the circuit response, checking whether the fault is constant or intermittent
Check for relevant technical service bulletins or calibration updates for that model and transmission

How to fix

Repair or replace damaged wiring and fix any short to voltage or open circuit
Clean or replace corroded or damaged connectors and terminals
Replace the 1-2 shift solenoid, or the solenoid assembly where it is only supplied as a unit
Replace the internal transmission harness if it is found to be faulty (depends on transmission)
Change the fluid and filter and clean the valve body if contamination is found, using the correct fluid for the transmission
Repair or replace the control module only after the wiring and solenoid have been proven good, then clear the code and road test

Can I keep driving?

Medium severity

The car can usually be driven carefully a short distance, but the transmission may shift harshly or go into limp mode. Get it checked soon, because continued driving with poor shifting can cause further transmission wear.

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