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DTC codes / GM codes / P1743

P1743 · GMTP Signal From ECM

P1743 on GM vehicles means the transmission control module (TCM) is not receiving a valid throttle position (TP) signal from the engine control module (ECM) over the controller area network (CAN) or serial data link. The TCM uses throttle position to schedule shift points and line pressure, so when the signal is missing or implausible the TCM sets this code and typically commands a default or limp-home shift strategy.

SystemPowertrain
Code typeGM specific
SeverityMedium
Fix difficultyProfessional
AreaTransmission

Symptoms you may notice

  • The malfunction indicator lamp (MIL) illuminates, often with no other noticeable symptoms besides the warning light
  • Harsh or delayed shifts as the transmission defaults to a fixed line pressure and shift schedule
  • The transmission may stay in a single gear or refuse to downshift when the accelerator is pressed
  • Reduced engine power or a limp-home mode message on the driver information center
  • Poor fuel economy and sluggish acceleration because the TCM cannot anticipate throttle changes
  • In some cases the vehicle starts and drives normally until the code is stored after a cold start or a specific driving cycle

Common causes, most likely first

  1. A faulty or intermittent throttle position sensor (TPS) on the engine side, causing the ECM to broadcast an invalid TP signal
  2. Wiring damage or corrosion in the CAN or serial data circuit between the ECM and TCM, including chafed harnesses and poor grounds
  3. A failing ECM that cannot correctly process or transmit the throttle position signal to the TCM
  4. A failing TCM that misinterprets a valid TP message or has an internal communication fault
  5. Low or contaminated transmission fluid causing the TCM to set related communication codes alongside P1743
  6. A weak or failing battery or charging system that drops voltage during cranking and disrupts module communication
  7. Aftermarket electronic throttle controllers or piggyback tuners that interfere with the factory TP signal

How to diagnose and fix it

  1. Connect a scan tool and record all stored and pending codes in both the ECM and TCM, then check for related throttle or communication codes before clearing anything
  2. Inspect the battery, charging system, and all ground straps for voltage drops that could disrupt module communication
  3. Visually inspect the engine and transmission harnesses for chafing, corrosion, or loose connectors at the ECM and TCM
  4. Use a scan tool to view live throttle position data from both the ECM and TCM and compare the two readings while slowly pressing the accelerator
  5. Perform a wiggle test on the TP sensor connector and the ECM-to-TCM data wiring while watching live data for dropouts
  6. If the TP signal is invalid at the ECM, diagnose and replace the throttle position sensor or the accelerator pedal assembly as applicable
  7. If the TP signal is valid at the ECM but missing at the TCM, perform a CAN bus integrity test and repair or replace the affected module or wiring

What the TP signal code really tells you

  • P1743 is a communication code, not a transmission mechanical fault, so replacing solenoids or rebuilding the transmission before checking the data link wastes money and does not fix the root cause
  • A dirty or failing throttle body on some GM engines can produce an implausible TP reading that the ECM broadcasts, setting P1743 without any TPS sensor fault code
  • Intermittent battery voltage drops during cranking are a common hidden cause because modules that brown out during start-up can log communication codes like P1743
  • Aftermarket remote starters and alarm systems spliced into the data bus frequently corrupt the TP message and trigger this code on otherwise healthy vehicles
  • The TCM may store P1743 as a history code after a single low-voltage event, so always check the freeze-frame data and battery health before condemning a module

Can I keep driving with P1743?

You can usually drive the vehicle to a repair shop, but expect harsh shifts or a limp-home mode and avoid heavy acceleration or towing until the fault is repaired. If the transmission drops into a single gear or the engine enters reduced power mode, limit driving to a short distance at low speed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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