P0700: Transmission Control System (MIL Request)
P0700 means the transmission control module has stored its own emission-related fault and asked the engine computer to turn on the check engine light. The code itself is only a notice, so how serious it is depends on the real fault stored in the transmission module, which you need a capable scan tool to read.
You can drive, but get it checked soon
P0700 alone does not cause limp mode, but the hidden transmission fault could be anything from minor to serious. If the car shifts normally, short drives to get it scanned are reasonable. If you notice harsh or delayed shifts, slipping or limp mode, stop driving it and have it checked, since continued driving can damage the transmission.
What it means
Many cars have a separate computer for the transmission, called the transmission control module. When it detects an emission-related problem, such as a faulty sensor, solenoid (an electrically operated valve), gear ratio error or speed sensor fault, it stores a specific code and sends a message to the engine computer to light the check engine light. The engine computer then logs P0700. A basic OBD reader often shows only P0700 and not the transmission code behind it. The details depend on the manufacturer: on GM systems the engine module reads the request from 3 seconds after start, and on Subaru-based systems the light comes on at once and goes out after three fault-free cycles. Ford engine modules with built-in transmission control do not use P0700. If the car goes into limp mode (reduced power and fixed gears to protect the transmission), that comes from the transmission fault, not from P0700.
Likely causes
- Actual fault stored in the transmission module (sensor, solenoid, ratio, speed sensor)Very likely
P0700 exists only because the transmission module logged a fault of its own, so that fault is the most likely cause.
- Wrong transmission fluid level or conditionPossible
Low or worn fluid can cause slipping or gear ratio codes, which in turn trigger the MIL request.
- Harness or connector at the transmission corroded or damagedPossible
Damaged wiring or connectors can interrupt sensor or solenoid signals and set a transmission fault.
- Low system voltage or weak batteryLess likely
Unstable voltage can upset the control modules and cause false or intermittent faults.
- Transmission module or software faultyLess likely
A failing module or faulty software can store faults or send the request incorrectly.
What you may notice
- Check engine light on, possibly with a transmission warning light
- Limp mode, harsh shifts or delayed shifts, depending on the transmission fault
- Often no symptoms at all if the fault was intermittent
- A simple OBD reader shows only P0700
What to check, cheapest first
- 1Note whether the car shifts normally or shows harsh shifts, delayed shifts or limp mode. · you can do it
- 2Check the transmission fluid level and condition if your vehicle has a dipstick, following the owner's manual. · you can do it
- 3Check the battery and charging voltage, and look for a weak battery or loose terminals. · you can do it
- 4Read the codes from the transmission module with a scan tool that can address it, since a basic reader will show only P0700. · mechanic
- 5Inspect the wiring and connectors at the transmission for corrosion, damage or moisture. · mechanic
- 6Repair the specific transmission fault found, then clear the codes and confirm P0700 does not return. Check for module or software issues if no other fault is found. · mechanic
Related codes
Frequently asked questions
Can I drive with P0700?+
Cautiously. If the car shifts normally, short trips to get it scanned are usually reasonable. If it slips, shifts harshly or goes into limp mode, stop driving and get it checked.
Can a loose gas cap cause P0700?+
No. P0700 is a request from the transmission module to light the check engine light, so the cause is a transmission-side fault, not the fuel system.
Will P0700 pass an emissions test?+
Probably not. The code is emissions-relevant and keeps the check engine light on, so the underlying transmission fault should be fixed first.
Why does my scanner show only P0700?+
The real fault is stored in the transmission module, and many simple OBD readers cannot read it. You need a tool that can communicate with the transmission module.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10