P1790

What it means

P1790 on a Cadillac means the transmission control module (TCM) has failed its internal checksum test. The module checks its stored program and calibration data when powered up, and the calculated value did not match the expected value. This points to corrupted or faulty memory or software in the module, or a supply problem that interrupted its self-test.

Symptoms

• Check engine or transmission warning light on
• Harsh, delayed or erratic gear changes
• Transmission stuck in one gear (limp mode)
• Loss of normal shift scheduling or torque converter lock-up
• Speedometer or gear indicator behaving oddly on some models
• Fault returns soon after being cleared

Possible causes

• Internal fault or corrupted memory in the transmission control modulelikely
• Outdated, corrupted or incomplete TCM calibration or software, for example after an interrupted updatepossible
• Low or unstable battery voltage or poor power and earth supply to the TCM during start-uppossible
• Corroded or loose connectors at the TCM, or water ingress into the module or its housingpossible
• Voltage spikes from a faulty charging system or poor jump-start or battery work damaging the modulerare
• Wiring damage on the TCM power, earth or communication circuitsrare

How to diagnose

1. Read all stored codes and freeze frame data, and note whether P1790 is current or history and whether other TCM or network codes are present.
2. Test battery condition and charging voltage, and correct any low-voltage or charging fault before going further.
3. Inspect the TCM power and earth connections and connectors for corrosion, looseness, heat damage or moisture, following the model-specific wiring layout.
4. Check the TCM fuses and relays and measure voltage drop on the supply and earth circuits.
5. Clear the code, cycle the ignition and road test to see whether it returns immediately or only under certain conditions.
6. Check whether a calibration or software update is available for the vehicle, and that the TCM part and calibration numbers are correct for the model and transmission.
7. Check for related communication faults on the vehicle network that could point to a wider power or module problem.

How to fix

• Repair any battery, charging, fuse, power or earth fault found, then recheck the code.
• Clean, repair or replace corroded or damaged connectors and wiring to the TCM, and fix any source of water ingress.
• Reprogram the TCM with the latest correct calibration where an outdated or corrupted calibration is the cause.
• Replace the TCM if the fault persists, and program and set it up for the vehicle as required for the model.
• Complete any related transmission relearn or adaptation procedure after repair, as specified for the model.

Can I keep driving?

This code for other makes

• P1790AcuraTCM A/T TP Sensor Circuit Fault
• P1790BuickTransmission Control Module Checksum
• P1790ChevroletTransmission Control Module Checksum
• P1790GMTransmission Control Module Checksum
• P1790GMCTransmission Control Module Checksum
• P1790HondaTCM A/T TP Sensor Circuit Fault
• P1790InfinitiTCM A/T TP Sensor Circuit Fault
• P1790JaguarIgnition Supply Malfunction
• P1790MazdaTP Mechanical Circuit
• P1790NissanTP Mechanical Circuit
• P1790OldsmobileTransmission Control Module Checksum
• P1790OtherTP (Mechanical) Circuit Malfunction
• P1790SaturnTransmission Control Module Checksum
• P1790VolkswagenTransmission Range Display Circuit Open

Nearby codes

• P1780CadillacPark/Neutral Position (PNP) Switch Circuit Engine Torque Signal Circuit
• P1791CadillacTransmission Control Module Loop