Skip to content
GTECH Calibration
Portal

P1790

Transmission Control Module Checksum.

  • GM
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
7
AreaTransmission
90
FaultThe specific fault in that area

What it means

On GM vehicles, P1790 means the Transmission Control Module (TCM) has failed its internal checksum test. The module checks the integrity of its stored program and calibration data and found a mismatch, so it cannot trust its own memory. This is a fault inside the control unit's software or memory, or a result of a power or programming problem, rather than a sensor or wiring fault in the transmission.

Symptoms

  • Malfunction indicator lamp or transmission warning lamp on
  • Harsh, delayed or erratic gear changes
  • Transmission stuck in one gear (limp mode)
  • Loss of normal shift strategy or incorrect shift points
  • Fault code returns soon after being cleared
  • Possible communication problems with other modules

Possible causes

  • Internal fault in the TCM (corrupted memory or failed processor)likely
  • Corrupted or incomplete software or calibration, for example after an interrupted programming sessionpossible
  • Low or unstable battery voltage or poor power and earth supply to the TCMpossible
  • Outdated calibration with a known checksum issue (depends on model and year)possible
  • Water ingress or corrosion in the TCM or its connectorrare
  • Voltage spikes from a faulty charging system or poor connectionsrare

How to diagnose

  1. Read all stored codes and freeze frame data, and note whether P1790 is current or history, and whether other power, communication or transmission codes are present.
  2. Check battery condition and charging voltage, as low or unstable voltage can corrupt module memory.
  3. Inspect the TCM connectors, wiring, fuses, power feeds and earths for corrosion, damage, water ingress or looseness.
  4. Clear the code and road test to see whether it returns immediately or only intermittently.
  5. Check whether a service bulletin or calibration update exists for the specific model, engine and transmission type.
  6. Check the module's software and calibration part numbers and whether any previous programming was completed correctly.
  7. Carry out a power and earth voltage-drop test at the TCM under load.
  8. If the code is persistent and supplies are good, test or substitute the TCM following the manufacturer's procedure.

How to fix

  • Repair any damaged wiring, poor connections or corroded terminals found on the TCM supply and earth circuits.
  • Charge or replace a weak battery and repair any charging system fault.
  • Reprogram the TCM with the latest correct calibration where an update is available or the software is corrupted.
  • Replace the TCM and program or set it up to the vehicle if it is internally faulty (model-specific procedure).
  • Dry out and repair water damage at the connector or module location, and fix the source of the leak.

Can I keep driving?

Medium severity

The car can usually be driven carefully for a short time, but it may go into limp mode or shift harshly, which can stress the transmission. Get it checked soon and avoid heavy loads or long journeys until it is resolved.

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

This code for other makes

Nearby codes