Damaged, chafed or corroded wiring or connectors between the TCM and the gearbox (solenoids, sensors, range switch); Low or failing battery or poor charging, causing unstable supply voltage to the TCM; Faulty shift solenoid, pressure control solenoid or internal gearbox wiring harness; Faulty transmission range or gear selector switch, or speed sensor; Poor power or earth supply to the TCM, including blown fuses or corroded earth points; Water ingress or fluid contamination in the gearbox connector or valve body electronics (mechatronic unit on some designs); Internal fault in the TCM or outdated software calibration where the manufacturer has issued an update.

P0702

Transmission Control System Electrical.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
7: AreaTransmission
02: FaultThe specific fault in that area

What it means

P0702 is the generic code for an electrical fault in the transmission control system. The transmission control module (TCM), or the engine control unit on some vehicles, has detected a problem in the electrical side of the transmission control circuits that does not fit a more specific code. It is a broad code, so the exact trigger depends on the make, model and gearbox type.

Symptoms

Gearbox warning light or malfunction indicator lamp on
Gearbox stuck in one gear (limp mode)
Harsh, delayed or erratic gear changes
No upshifts or no manual or sport mode
Reduced power or poor fuel economy
Gearbox selector or display showing a fault message

Possible causes

Damaged, chafed or corroded wiring or connectors between the TCM and the gearbox (solenoids, sensors, range switch)likely
Low or failing battery or poor charging, causing unstable supply voltage to the TCMlikely
Faulty shift solenoid, pressure control solenoid or internal gearbox wiring harnesspossible
Faulty transmission range or gear selector switch, or speed sensorpossible
Poor power or earth supply to the TCM, including blown fuses or corroded earth pointspossible
Water ingress or fluid contamination in the gearbox connector or valve body electronics (mechatronic unit on some designs)possible
Internal fault in the TCM or outdated software calibration where the manufacturer has issued an updaterare

How to diagnose

Read all stored codes and freeze frame data from both the engine and transmission control units, and note any other codes that point to a specific circuit
Check battery condition and charging voltage, and fix any supply problems before further diagnosis
Inspect the gearbox wiring, connectors and plugs for damage, corrosion, fluid leaks or water ingress
Check the relevant fuses, relays and earth connections for the TCM and gearbox
Check the gearbox fluid level and condition, following the manufacturer's procedure for that model
Use live data to compare gear selector position, input and output speed and solenoid commands with expected values
Test solenoid, sensor and range switch circuits for resistance, continuity and shorts using the manufacturer's specifications
Check for technical service bulletins or software updates for the model and gearbox before condemning the TCM

How to fix

Repair or replace damaged wiring and clean or replace corroded connectors
Replace a weak battery or repair the charging system
Replace the faulty solenoid, sensor, range switch or internal harness as identified by testing
Restore good power and earth connections to the TCM, and replace blown fuses once the cause is found
Correct fluid level or condition problems and fix any leak that is causing contamination
Replace or reprogram the TCM, or apply a manufacturer software update, only where testing or a bulletin confirms this as the cause

Can I keep driving?

Medium severity

The car can usually be driven carefully for a short time, especially if it has gone into limp mode, but get it checked soon. Continued driving with erratic shifting or a stuck gear risks further gearbox damage and may be unsafe in traffic.

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