P0700 Code: Transmission Control System Malfunction (Request for MIL Illumination)

What the P0700 code means

Vehicles with an electronically managed automatic transmission have a dedicated module, the TCM. That module has its own fault memory, and a basic emissions code reader does not read it.

So the driver finds out something is wrong, the TCM sends a request to the engine computer. The engine computer turns on the check engine light and stores the P0700 code, which means exactly this: there are codes stored in the transmission, go read them there.

That is why it makes no sense to look for a repair for the P0700 code itself. The useful code is the one behind it. It could be a shift solenoid, a speed sensor, line pressure or the torque converter.

One point needs clearing up because it causes constant confusion. This code can stay stored in the engine module even after the transmission problem has been repaired. The engine computer keeps it until the transmission module stops sending the request and a verification cycle is completed.

That is why clearing the code from the engine module is not enough. You also have to clear it from the transmission module, and then drive until the transmission goes through all of its gears at normal operating temperature. Only then does the light go out for good.

P0700 code symptoms

• Check engine light on and, on many vehicles, the transmission warning light too.
• Harsh shifts, late shifts or shifts that never happen.
• Limp mode with only one gear available, normally third.
• Transmission slipping when you accelerate.
• Vibration at a steady speed if the torque converter is involved.
• Higher fuel use.
• The code stays after the transmission is repaired if it was not also cleared in its own module.
• Shifts that get harsher when the fluid is cold and improve as it warms up.

Likely causes of the P0700 code

1. Low level or poor condition of the transmission fluid. Always the first check.
2. Defective shift or pressure solenoids.
3. Faulty input or output speed sensors.
4. Fluid temperature sensor out of range.
5. Worn or clogged valve body.
6. Damaged wiring or module connector.
7. Torque converter with a defective lockup clutch.
8. Failed TCM, or one with outdated software.
9. Internal clutch wear in high mileage transmissions.
10. Clogged transmission cooler, which drives the fluid temperature up and sets intermittent codes.
11. Weak battery, which makes the module reset and sets codes that look random.
12. Outdated module software compared with a revision released by the manufacturer.

How to diagnose the P0700 code step by step

1. Read the codes in the transmission module. You need a scan tool that reaches all modules, not just the emissions one. Without this step no diagnosis is possible.
2. Check the fluid level and condition. Dark fluid that smells burnt or carries particles points to internal wear.
3. Look at the freeze frame data to learn the gear, temperature and speed when the fault happened.
4. Watch the input and output speeds in live data. An abnormal difference between the two means slipping.
5. Check the fluid temperature while driving. Overheating explains many intermittent faults.
6. Inspect the wiring harness and connectors at the transmission, which are very exposed to heat and moisture.
7. Check whether a software update exists for the module on your vehicle.
8. Clear the codes in the transmission module too, not just in the engine module, or the light will stay on after the repair.
9. Check the fluid temperature during sustained driving. Above 120 degrees C (248 degrees F) the fluid breaks down and sets intermittent codes.
10. Rule out a weak battery, which makes the module reset and sets codes with no real mechanical fault.

How to fix the P0700 code

• Correct the fluid level or do a complete fluid change with the exact fluid the manufacturer specifies. The wrong fluid causes shifting faults all by itself.
• Replace the defective solenoids identified by the TCM codes.
• Replace the faulty speed sensors.
• Clean or replace the valve body when the diagnosis points to it.
• Repair damaged wiring and clean the connectors.
• Update the module software if the manufacturer released a revision.
• Consider rebuilding the transmission if internal wear is confirmed.
• Clean or replace the transmission cooler if the fluid temperature is excessive.
• Clear the codes in both modules and take a drive that covers all gears before you call the job finished.
• Check whether a module software update exists before replacing mechanical parts.

Technical reference data

• P0700 is an informational code: there is always at least one additional code in the transmission module.
• Normal fluid operating temperature: 70 to 100 degrees C (158 to 212 degrees F). Above 120 degrees C (248 degrees F) the fluid breaks down quickly.
• Typical shift solenoid resistance: 10 to 30 ohms.
• Input and output speeds should keep a constant ratio in each gear.
• The code is kept in the engine module until the transmission stops sending the request.
• Verification: a drive that covers all gears with the fluid at operating temperature.

Brand-specific notes

Transmission fluid type is not interchangeable between manufacturers or even between models. Putting a universal fluid in a transmission that requires a specific specification causes shifting faults and codes that no replacement part will fix.

Many inexpensive scan tools clear only the engine module codes. If the light comes right back after you clear it, make sure your tool also reaches the transmission memory. A P0700 code that returns immediately is often just the old request still sitting in the engine module.

Frequently asked questions about P0700