Damaged, chafed or corroded wiring in the torque reduction signal circuit between TCM and ECM/PCM; Poor connection at the TCM or ECM/PCM connector (bent, spread or corroded terminals, water ingress); Open or short to ground or voltage on the signal wire; Low battery voltage or poor earth connections upsetting module signals; Faulty ECM/PCM unable to receive or respond to the torque reduction request; Faulty TCM, or an outdated TCM or ECM calibration where the manufacturer lists one as a known cause.

P1844

Torque Reduction Signal Circuit Desired By TCM.

Buick
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 Buick means a fault in the torque reduction signal circuit that the transmission control module (TCM) uses to ask the engine control module (ECM/PCM) to briefly cut engine torque during gear changes. The TCM has detected that this request signal is not behaving as expected, for example open, shorted or implausible. Exact circuit layout and wiring depend on the model, engine and year.

Symptoms

Harsh or flared gear changes, especially under load
Delayed or abrupt shifts
Malfunction indicator lamp or transmission warning lamp on
Transmission may default to a fixed gear or limp mode
Reduced smoothness or power during upshifts
Possible traction or stability control messages on some models

Possible causes

Damaged, chafed or corroded wiring in the torque reduction signal circuit between TCM and ECM/PCMlikely
Poor connection at the TCM or ECM/PCM connector (bent, spread or corroded terminals, water ingress)likely
Open or short to ground or voltage on the signal wirepossible
Low battery voltage or poor earth connections upsetting module signalspossible
Faulty ECM/PCM unable to receive or respond to the torque reduction requestrare
Faulty TCM, or an outdated TCM or ECM calibration where the manufacturer lists one as a known causerare

How to diagnose

Read all stored and pending codes plus freeze frame data, and note any engine or other transmission codes that appear alongside P1844
Check battery condition and charging voltage, and inspect main earth connections
Visually inspect the wiring between the TCM and ECM/PCM for chafing, heat damage, rubbed insulation and previous repairs
Disconnect and inspect the TCM and ECM/PCM connectors for corrosion, moisture and pin tension
Using the model-specific wiring diagram, test the torque reduction signal wire for continuity, and for shorts to ground and to voltage
Monitor the torque reduction request and actual engine response on a scan tool during a road test, if the vehicle supports it
Check for applicable technical service bulletins and calibration updates for the specific model and engine
Clear the code and road test to see whether it returns before condemning any module

How to fix

Repair or replace damaged wiring in the torque reduction signal circuit
Clean, repair or replace faulty connectors and terminals
Restore good battery voltage and earth connections
Update the TCM or ECM/PCM calibration only if a published bulletin lists it as the fix for this fault
Replace or reprogram the faulty TCM or ECM/PCM once wiring and power supplies are proven good

Can I keep driving?

Medium severity

The car can usually be driven carefully for a short time, but harsh shifts or limp mode can stress the transmission, so have it diagnosed soon. Avoid heavy loads and towing until it is fixed.

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