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P1790

Transmission Control Module Checksum.

  • Saturn
  • 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 Saturn models, P1790 means the Transmission Control Module (TCM) has failed its internal checksum test. The module checks its stored program and calibration data when it powers up and during operation, and the stored data did not match the expected value. This points to a fault inside the TCM or its memory, or to an interrupted data write or power supply problem.

Symptoms

  • Transmission warning light or check engine light on
  • Transmission stuck in one gear (limp-home mode)
  • Harsh, delayed or erratic gear changes
  • No torque converter lock-up, with poorer fuel economy
  • Speedometer or shift behaviour inconsistent
  • Code returns soon after being cleared

Possible causes

  • Internal fault in the TCM memory or processorlikely
  • Corrupted or outdated TCM software or calibration, for example after an interrupted reprogrammingpossible
  • Low or unstable battery voltage or poor TCM power and earth connectionspossible
  • Corroded, loose or damaged TCM connector pins or wiringpossible
  • Water ingress or heat damage to the TCM (position and type depend on model and transmission)rare
  • Voltage spikes from a faulty charging system or poor jump-startrare

How to diagnose

  1. Read all stored codes and freeze frame data, and note whether P1790 is current or history, and whether other transmission or network codes are present
  2. Check battery condition and charging voltage, as low or unstable voltage can corrupt module data
  3. Inspect the TCM connectors, wiring and fuses for corrosion, moisture, damage or loose pins, following the model-specific location
  4. Check the TCM power feeds and earth connections for voltage drop under load
  5. Clear the code, road test and see if it returns immediately or only intermittently
  6. Check for any available software or calibration updates for the vehicle and transmission type
  7. Confirm the fault is persistent before condemning the module, as procedure depends on model and transmission

How to fix

  • Repair or clean any damaged wiring, connectors, power or earth faults found
  • Repair or replace the battery or charging system if voltage is unstable
  • Reprogram the TCM with the correct up-to-date calibration if the software is corrupted or outdated, with stable supply voltage during the process
  • Replace the TCM if the fault is confirmed internal, then programme and set it up as the model requires
  • Dry out and repair the source of any water ingress before fitting a replacement module

Can I keep driving?

Medium severity

The car can usually be driven carefully if it shifts normally, but expect limp-home mode or poor shifting. Have it checked soon, as the transmission may behave unpredictably and could suffer wear or leave you stranded.

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

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