P0702: Transmission Control System Electrical Fault
P0702 means the car's computer found an electrical fault somewhere in the transmission control system, most often in the power supply to the transmission's shift solenoids (small electric valves that control shifting). It is a moderate to serious code because the transmission can drop into a fixed limp gear, so have it checked soon.
You can drive, but get it checked soon
If the transmission is shifting normally, short, gentle trips to get it checked are reasonable. If it is stuck in one gear, shifts harshly or not at all, avoid driving it, because limp mode limits speed and acceleration and can make it hard to merge or climb hills safely.
What it means
P0702 is a general electrical fault code for the transmission control system as a whole. It usually points to the power supply of the transmission actuators, such as the solenoid supply, the transmission relay, or a supply switch inside the control module. It can also be set by a circuit fault that cannot be assigned to one single part. Faults in individual solenoids get their own codes (P0750 and following), and actuator supply faults are covered by P0657 and following. If the solenoid supply is lost, transmissions usually fall back to a hydraulic limp gear, a fixed gear that works without electronic control. The code does not by itself turn on the check engine light on every vehicle. Some makers store it without the light, so a car can have this code and show no dashboard warning.
Likely causes
- Transmission actuator supply interrupted (fuse, relay, ground)Very likely
The solenoids need steady power and a good ground, so a blown fuse, failed relay or bad ground connection cuts the supply and sets this code.
- Harness or connector at transmission or module damaged, corroded or oil-soakedPossible
Damaged, corroded or oil-soaked wiring and plugs can break or weaken the electrical connection between the module and the transmission.
- Transmission module output stage or supply switch faultyPossible
The module has internal switches that feed power to the actuators, and if one fails the module reports a fault in the whole system.
- Low or fluctuating system voltageLess likely
A weak battery or charging problem can drop voltage below what the transmission electronics need and trigger the fault.
What you may notice
- Transmission stuck in a fixed gear (limp mode)
- Transmission warning light, and on some makes the check engine light
- No shifts or harsh shifts
- Additional solenoid-related codes stored alongside P0702
What to check, cheapest first
- 1Check the battery and charging voltage, and look for other stored codes such as P0560, P0700 or P0701 that point to a voltage or general transmission problem. · you can do it
- 2Find the transmission control fuse and relay in the fuse box (see the owner's manual) and inspect them for a blown fuse or a damaged relay. · you can do it
- 3Visually inspect the wiring and connector at the transmission and at the control module for damage, corrosion, loose pins or oil contamination. · you can do it
- 4Read all codes with a scan tool, including P0657 and P0750 series codes, to see whether the fault is in the supply or in a single solenoid. · mechanic
- 5Measure supply voltage and ground at the transmission connector and the relay circuit to find where power is lost. · mechanic
- 6If wiring, fuses and voltage are good, test the transmission module's output stage and supply switch, and repair or replace the module if it is faulty. · mechanic
Related codes
Frequently asked questions
Can I drive with a P0702 code?+
Only with caution. If the transmission shifts normally, short trips to a shop are usually fine. If it is in limp mode or shifting harshly, avoid driving it.
Can a loose gas cap cause P0702?+
No. A gas cap affects the fuel vapor system, not the transmission electrical circuits.
Will P0702 fail an emissions test?+
The code is not classed as emissions relevant and does not necessarily turn on the check engine light. If the light is on for any reason, many emissions tests will still fail the car.
How hard is it to fix?+
Difficulty is medium, and it is not recommended as a DIY job. Time ranges from about half an hour for a simple fuse or relay fix up to around 4 hours for wiring or module work.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10