TCU · TRANSMISSION SENSORS · GEAR SELECTION
A gearbox warning, harsh change or loss of drive needs a scan of the transmission controller as well as the engine. A single generic code can hide the detail needed to separate an electrical problem from a hydraulic or mechanical one.
Five useful starting points
P0700 concerns transmission control. P0715 concerns the input/turbine speed-sensing circuit; P0716 flags its range or performance. P0720 concerns output-speed sensing. P0730 indicates an unexpected gear ratio. Confirm the exact wording and suffix against your gearbox documentation.
Reference: HELLA powertrain code reference. For a VAG-specific P0716 example, Ross-Tech discusses G182 signal plausibility and identifies wiring, connections and the sensor as diagnostic considerations.
What to record for the technician
- Which gears work and whether the fault affects reverse.
- Whether it appears cold, hot, during a shift or when first selecting drive.
- The full transmission scan, including intermittent/current status.
- Gearbox identification and controller hardware/software details.
- Recent fluid work, clutch work, wiring repairs or module replacement.
Why the ratio code is different
An unexpected ratio describes an observed relationship; it does not by itself identify a failed ECU. The workshop must compare relevant speed data and investigate the applicable transmission system. Sending the electronics for a bench assessment cannot replace vehicle-side checks when the cause has not been isolated.
DSG and other automatic gearboxes
“Automatic” and “seven-speed DSG” are not sufficient identifiers for choosing parts or a procedure. Read our gearbox identification guide. Keep the original TCU and confirm donor compatibility before purchasing a replacement.
Next step
Use our TCU and gearbox electronics service to discuss the scan and completed checks. If the vehicle loses drive or behaves unpredictably, stop testing it on the road and arrange appropriate recovery or workshop assistance.
Send AXION your diagnostic details
For a Didcot workshop enquiry or a suitable UK postal module assessment, send the vehicle model, year, engine or gearbox, full module label, complete scan report and a description of what happened. Include previous battery work, programming, water ingress or replacement parts. Please agree suitability before removing or posting a unit.