Open circuit or poor connection in the 1-2 shift solenoid wiring or connector; Faulty 1-2 shift solenoid (open internal winding); Damaged internal transmission wiring harness or pass-through connector, often affected by fluid contamination; Wiring shorted to a voltage supply; Low, degraded or contaminated transmission fluid affecting the solenoid and connector; Faulty transmission control module or internal driver.

P1843

1 2 Shift Solenoid Circuit High Voltage.

GMC
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 GMC means the transmission control module has detected a high voltage condition in the 1-2 shift solenoid circuit. The module monitors the voltage on the solenoid control circuit and sets the code when it reads higher than expected, which usually points to an open circuit, a short to voltage or a failed solenoid or driver. The exact solenoid layout and wiring depend on the model, engine and transmission fitted.

Symptoms

Transmission warning light or check engine light on
Harsh, delayed or missing 1-2 upshift
Transmission stuck in one gear or in a limp-home mode
Poor acceleration or flaring between gears
Worse fuel economy
Shift feel changes when the transmission is hot or cold

Possible causes

Open circuit or poor connection in the 1-2 shift solenoid wiring or connectorlikely
Faulty 1-2 shift solenoid (open internal winding)likely
Damaged internal transmission wiring harness or pass-through connector, often affected by fluid contaminationpossible
Wiring shorted to a voltage supplypossible
Low, degraded or contaminated transmission fluid affecting the solenoid and connectorpossible
Faulty transmission control module or internal driverrare

How to diagnose

Read all stored codes and freeze frame data, noting transmission temperature, speed and whether other solenoid or communication codes are present
Check the transmission fluid level and condition against the manufacturer's procedure for the model, looking for burnt smell, debris or discolouration
Inspect the external transmission connector and wiring for damage, corrosion, fluid ingress, chafing and bent or pushed-back pins
Check battery condition and charging voltage, as low or unstable supply can upset the circuit readings
Measure the solenoid resistance at the transmission side and compare it with the specification for that transmission
Test the control circuit for continuity, short to voltage and short to ground between the connector and the control module, following the wiring diagram
Check the internal harness and solenoid connector, which may need the pan or valve body accessed, depending on the model
Clear the code and road test, watching live data to see whether it returns and under what conditions

How to fix

Repair or replace damaged wiring, terminals or connectors in the solenoid circuit
Replace the 1-2 shift solenoid if its resistance or operation is out of specification
Replace the internal wiring harness or pass-through connector if it is damaged or leaking
Correct fluid level or service the transmission with the correct fluid if contamination is found, and fix the source
Repair or replace the transmission control module only after wiring and solenoid faults are ruled out, then complete any required programming

Can I keep driving?

Medium severity

The car may be driven carefully for a short time if it shifts acceptably, but it may be in limp mode and prolonged use risks transmission wear. Get it diagnosed soon and avoid towing or heavy loads.

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