Weak or failing battery that cannot maintain stable voltage under load; Corroded, loose, or damaged battery terminals and ground connections; Blown fuse or faulty relay in the TCM power supply circuit; Damaged or chafed wiring harness between the battery, fuse box, and TCM; Faulty alternator not charging the battery sufficiently, causing low system voltage; Internal fault in the TCM power supply circuitry, though less common; Poor ground connection at the transmission or engine block

DTC codes / Kia codes / P1794

P1794 · KiaBattery Or Circuit Failure

Q: What does code P1794 mean?

Battery Or Circuit Failure. P1794 on a Kia means the transmission control module (TCM) has detected a problem with the battery power supply or its associated wiring circuit to the transmission control system. The TCM monitors voltage on its dedicated power feed and sets this code when the voltage falls outside the expected range, indicating a loss of power or a circuit fault rather than an internal transmission failure.

P1794 on a Kia means the transmission control module (TCM) has detected a problem with the battery power supply or its associated wiring circuit to the transmission control system. The TCM monitors voltage on its dedicated power feed and sets this code when the voltage falls outside the expected range, indicating a loss of power or a circuit fault rather than an internal transmission failure.

SystemPowertrain

Code typeKia specific

SeverityMedium

Fix difficultyIntermediate

AreaTransmission

Symptoms you may notice

Illuminated check engine light or transmission warning light on the dashboard
Often no symptoms besides the warning light, especially if the fault is intermittent
Harsh or delayed shifting as the TCM defaults to a limp-home mode
Transmission stuck in a single gear or refusing to downshift
Intermittent loss of power or stalling when electrical load is high
Battery warning light or dimming lights if the underlying issue is a charging system fault

Common causes, most likely first

Weak or failing battery that cannot maintain stable voltage under load
Corroded, loose, or damaged battery terminals and ground connections
Blown fuse or faulty relay in the TCM power supply circuit
Damaged or chafed wiring harness between the battery, fuse box, and TCM
Faulty alternator not charging the battery sufficiently, causing low system voltage
Internal fault in the TCM power supply circuitry, though less common
Poor ground connection at the transmission or engine block

How to diagnose and fix it

Perform a battery load test and check resting voltage; replace the battery if it fails
Inspect and clean battery terminals, ground straps, and engine-to-chassis grounds
Check the TCM fuse and relay in the under-hood fuse box and replace if blown or faulty
Measure voltage at the TCM power feed connector with the key on and engine running; compare to battery voltage
Inspect the wiring harness for chafing, corrosion, or loose connectors between the battery and TCM
Test the alternator output to confirm charging voltage is within specification
If all external circuits test good, perform a continuity and resistance test on the TCM ground circuit before condemning the TCM

What most technicians overlook on P1794

A battery that starts the engine fine can still set P1794 if its internal resistance rises and voltage sags briefly during cranking or under electrical load, so a simple crank test is not enough.
Corroded ground connections on the transmission bell housing or engine block are a frequent culprit that many technicians miss because they focus only on the positive battery cable.
P1794 does not automatically mean the TCM is bad; replacing the module without verifying power and ground circuits is an expensive misdiagnosis trap.
Intermittent P1794 codes often appear after battery replacement or jump-starting if the TCM adaptive memory is not reset, so clearing codes and performing a relearn may resolve the light.
A failing alternator diode can introduce AC ripple into the electrical system that disturbs the TCM even when average voltage looks normal on a basic voltmeter.

Can I keep driving with P1794?

You can usually drive the vehicle to a repair shop, but avoid long trips or heavy electrical loads because a failing power supply can cause the transmission to enter limp mode without warning. If the transmission is already shifting harshly or stuck in gear, limit driving to low-speed local roads and arrange service promptly.

Tools that help

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