Damaged, chafed or broken wiring in the gear ratio output circuit; Corroded, loose or contaminated connector at the transmission or control unit; Faulty speed or position sensor feeding the gear ratio calculation (model dependent); Internal wiring harness fault inside the transmission, possibly from fluid contamination; Low or degraded transmission fluid affecting shift behaviour and signals; Faulty powertrain or transmission control unit output driver.

P1845

Transmission Gear Ratio Output Circuit.

Oldsmobile
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 on an Oldsmobile is defined as a Transmission Gear Ratio Output Circuit fault. The control unit has detected an electrical problem in the circuit that outputs or reports the gear ratio information, such as an open circuit, a short or an implausible signal. The exact circuit and how it is monitored depend on the model, year and transmission, so confirm it against the factory wiring information for the vehicle.

Symptoms

Malfunction indicator lamp or transmission warning lamp on
Harsh, delayed or erratic gear changes
Transmission stuck in one gear or in a limp-home mode
Speedometer, cruise control or other gear-related functions behaving oddly
Poor fuel economy or unusual engine speed at cruise

Possible causes

Damaged, chafed or broken wiring in the gear ratio output circuitlikely
Corroded, loose or contaminated connector at the transmission or control unitlikely
Faulty speed or position sensor feeding the gear ratio calculation (model dependent)possible
Internal wiring harness fault inside the transmission, possibly from fluid contaminationpossible
Low or degraded transmission fluid affecting shift behaviour and signalspossible
Faulty powertrain or transmission control unit output driverrare

How to diagnose

Read all stored and pending codes and record the freeze frame data to see speed, gear and load when the code set
Check the transmission fluid level, condition and smell, and look for leaks around the transmission harness connector
Inspect the harness and connectors between the transmission and the control unit for chafing, heat damage, water ingress, corrosion and bent or pushed-back pins
Check for other speed sensor or transmission codes that point to a shared cause
Using the factory wiring diagram, test the circuit for continuity, shorts to ground or voltage, and correct supply and reference voltages
Compare live data for gear commanded, gear ratio and output speed against actual road speed on a test drive
Test the relevant sensors against their specification, and only suspect the control unit once wiring and sensors are proven good

How to fix

Repair or replace damaged wiring and fix any chafed sections, using proper soldered and sealed joints
Clean, repair or replace corroded or damaged connectors and terminals
Replace any speed or position sensor found to be out of specification
Correct the fluid level or service the transmission if the fluid is degraded, using the specified type
Repair or replace the internal transmission harness or connector if it is contaminated or faulty
Repair or replace the control unit only after the circuit and sensors have been proven good, then clear the code and road test to confirm

Can I keep driving?

Medium severity

Short, gentle journeys are usually possible, but get it checked soon because shifting problems or limp mode can put extra wear on the transmission. If shifting becomes harsh, the car will not change gear or it loses drive, stop driving it and have it recovered.

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