Damaged, chafed or corroded wiring in the gear ratio output circuit (open circuit, short to ground or short to voltage); Poor connection at the transmission connector or control unit plug, such as bent pins, water ingress or green corrosion; Low or contaminated transmission fluid affecting internal sensors or solenoids; Faulty speed or position sensor feeding the gear ratio calculation; Low battery voltage or poor earth connections upsetting control unit signals; Fault inside the transmission control unit or its output driver; Outdated control unit software where a known fault exists for that model.

P1845

Transmission Gear Ratio Output Circuit.

Chevrolet
Powertrain
Manufacturer code
Medium severity

How this code is built

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

What it means

P1845 is a Chevrolet manufacturer-specific code for a fault in the transmission gear ratio output circuit. The transmission control unit monitors the circuit that passes its gear ratio information on, and has seen a voltage or signal that does not match what it expects. The exact signal and which module receives it depend on the model, engine and transmission, so check the vehicle-specific data.

Symptoms

Check engine light or transmission warning light on
Harsh, delayed or erratic gear changes
Transmission stuck in one gear or in a limp-home mode
Wrong or flickering gear indication on the dash
Poor fuel economy or reduced performance
Traction or stability control warnings on some models

Possible causes

Damaged, chafed or corroded wiring in the gear ratio output circuit (open circuit, short to ground or short to voltage)likely
Poor connection at the transmission connector or control unit plug, such as bent pins, water ingress or green corrosionlikely
Low or contaminated transmission fluid affecting internal sensors or solenoidspossible
Faulty speed or position sensor feeding the gear ratio calculationpossible
Low battery voltage or poor earth connections upsetting control unit signalspossible
Fault inside the transmission control unit or its output driverrare
Outdated control unit software where a known fault exists for that modelrare

How to diagnose

Read all stored and pending codes and note the freeze frame data, including road speed, gear and fluid temperature. Look for other transmission or speed sensor codes.
Check battery condition, charging voltage and the main earth connections.
Check transmission fluid level and condition, following the procedure for that model, and look for leaks.
Inspect the wiring harness between the transmission and control unit for chafing, heat damage, rodent damage and water ingress.
Disconnect and inspect the transmission and control unit connectors for corrosion, bent or pushed-back pins and poor terminal tension.
Using the wiring diagram for the exact model, test the output circuit for continuity, short to ground and short to voltage.
Compare live gear ratio, input speed and output speed data on a scan tool while driving, to see if the sensors agree.
Check for software updates or technical bulletins for that model and transmission, then consider control unit testing only after the wiring and sensors are cleared.

How to fix

Repair or replace damaged wiring and fix any connector terminals found loose or corroded.
Clean, reseat or replace the affected connector if water or corrosion has damaged it.
Correct the transmission fluid level, or service the fluid as the manufacturer specifies if it is degraded.
Replace any faulty speed or position sensor confirmed by testing.
Restore good battery condition and repair poor earth connections.
If the control unit is proven faulty, or a known software fault applies, repair or replace the unit and update its software as required.

Can I keep driving?

Medium severity

The car can usually be driven carefully for a short time, but get it checked soon. If the gearbox is in limp mode, shifting harshly or slipping, limit driving, because continued use risks transmission damage.

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