This is a general code the engine ECU sets when the separate transmission control module (TCM) has reported its own internal fault. It's essentially a pointer telling you to go look at the transmission-specific codes stored in the TCM rather than diagnosing anything from this code alone.
Symptoms
- Transmission may enter "limp mode" — stuck in one gear (often 2nd or 3rd) to protect itself
- Harsh, delayed, or erratic gear shifts
- Transmission warning light on the dash, separate from the check engine light
- In some cases, no noticeable symptom beyond the warning light if the fault is minor
Likely causes
- This code alone doesn't identify a cause — it's a pointer to check the TCM's own stored codes
- Common underlying transmission faults include a failing shift solenoid, a range/position sensor issue, or a wiring problem in the transmission harness
- Low or degraded transmission fluid, which can trigger multiple transmission-side faults at once
How to diagnose it
- Scan for transmission-specific codes (typically P07xx range) using a scan tool capable of reading the TCM, not just the engine ECU
- Check transmission fluid level and condition — low or burnt fluid is a very common root cause across many transmission codes
- Follow up on whichever specific TCM code is found rather than treating P0700 itself as the diagnosis
Typical fixes & cost
- Transmission fluid and filter service, if fluid condition is poor100–300 EUR
- Repair the specific fault found in the TCM's stored codes (cost varies widely by fault)150–2000 EUR
Code names are compiled from open/standardized SAE and ISO references. Explanations, symptoms, causes and fixes are original. Covers generic (P0/C0/B0/U0) codes only — manufacturer-specific codes are planned for a future update.
AS
Reviewed by Artyom SemenovAutomotive Editor · Fact-checked by Yauheni Kapliarchuk, Editor-in-Chief