Damaged, chafed or corroded wiring in the torque reduction signal circuit between the TCM and engine control module; Poor connection or water ingress at the TCM or engine control module connectors; Fault with the engine control module's handling of the torque reduction request, such as a stored related engine code; Faulty TCM, or a fault inside the transmission control unit's output driver; Low or erratic system voltage or a poor earth affecting module communication; Outdated or faulty control module software calibration (model and year dependent).

P1844

Torque Reduction Signal Circuit Desired By TCM.

Cadillac
Powertrain
Manufacturer code
Medium severity

How this code is built

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

What it means

P1844 on a Cadillac means the transmission control module (TCM) has detected a fault in the torque reduction signal circuit. During gear changes the TCM asks the engine control module to briefly cut engine torque for a smoother shift. The code sets when that request signal is missing, out of range or not being acted on as expected.

Symptoms

Harsh or abrupt gear changes, especially under load
Flare or delayed shifts
Transmission warning light or check engine light on
Reduced shift quality or firmer shifts than normal
Transmission may default to a limp-home or fixed gear in some cases

Possible causes

Damaged, chafed or corroded wiring in the torque reduction signal circuit between the TCM and engine control modulelikely
Poor connection or water ingress at the TCM or engine control module connectorslikely
Fault with the engine control module's handling of the torque reduction request, such as a stored related engine codepossible
Faulty TCM, or a fault inside the transmission control unit's output driverpossible
Low or erratic system voltage or a poor earth affecting module communicationpossible
Outdated or faulty control module software calibration (model and year dependent)rare

How to diagnose

Read all stored and pending codes from both the transmission and engine control modules and note any related engine, communication or voltage codes.
Review freeze frame data and check whether the fault appears under load, during particular shifts or when hot or cold.
Check battery condition and charging voltage, and inspect main earth connections for security and corrosion.
Visually inspect the wiring harness and connectors at the TCM and engine control module for chafing, pin damage, corrosion or moisture.
Using the manufacturer's wiring diagram for the specific model and engine, test the torque reduction signal wire for continuity, short to earth and short to voltage.
Monitor the torque reduction request and engine response on a scan tool during a road test to see whether the signal is sent and acted on.
Check for applicable software updates or technical bulletins for the specific model and year.
If wiring and connections are sound, test the module outputs and consider module fault diagnosis according to the manufacturer's procedure.

How to fix

Repair or replace damaged wiring in the torque reduction signal circuit.
Clean, reseat or replace corroded or damaged connectors and terminals.
Restore good power and earth supplies by correcting charging or earth faults.
Fix any related engine control module faults that prevent the torque reduction request being actioned.
Update the module calibration if an outdated or faulty calibration is confirmed as the cause.
Replace and program the faulty control module only after wiring and supplies have been proven good.

Can I keep driving?

Medium severity

The car can usually be driven carefully for a short time, but harsh shifts can stress the transmission, so have it diagnosed soon. If the transmission goes into limp mode or shifts violently, limit driving and get it checked promptly.

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