P071B–P071E Transmission Mode Switch A Circuit Low
The voltage on this circuit is sitting near zero. Typically a short to earth, or a sensor that has failed to its low end.
Can you drive it? The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.
Which code is which
Same fault, different cylinder or bank — diagnosed the same way. Several set together usually means one shared cause.
| Code | Definition | Severity |
|---|---|---|
P071B | Transmission Mode Switch A Circuit Low | Investigate soon |
P071E | Transmission Mode Switch B Circuit Low | Investigate soon |
The definition
P071B: Transmission Mode Switch A Circuit Low.
P071B is a powertrain code (the engine or gearbox), defined by the SAE standard - it means the same thing on any make of car, and any generic OBD-II reader will decode it.
What to check first
Cheapest and fastest checks first:
- Unplug the sensor. If the reading jumps to full scale, the wiring is fine and the sensor has failed low.
- Check the sensor's 5V supply and its earth before condemning the sensor itself.
What actually causes this on a VAG
Official definition: Transmission Mode Switch "A" Circuit Low. The gearbox control unit reads the driving-programme or mode switch, and this code means that signal is sitting lower than it should - effectively being pulled to earth. Which switch that is varies by model (a sport or programme button, a drive-mode selector, or mode contacts in the selector assembly), and it is not the same thing as the Tiptronic manual gate, which has its own separate fault codes on these cars. The car normally responds by ignoring the mode you select and running a default automatic programme, so it still drives perfectly well - the selection simply has no effect. This is an electrical fault in the switch or its wiring, not damage inside the gearbox.
Most likely causes, in order
- Liquid or contamination in the gear lever assembly. A spilled drink running down into the lever is a genuine and very cleanable cause: the residue bridges contacts to earth and holds the signal low. Look for sticky residue or staining around the base of the lever. Caught early this is usually a cleaning job rather than a parts job, which is why it is worth checking before anything is ordered.
- Corroded connector or water under the console carpet. Leaking sunroof drains, door seals or a blocked scuttle drain can leave water tracking under the front carpet. Damp carpet in the console area alongside this fault points at corrosion in the connector rather than a failed switch - and at a leak that needs fixing too, or it will come back.
- Chafed wiring shorting to earth. The loom to the selector moves with the lever and passes under carpet and near seat rails, where it can be pinched or worn through against a bracket. Check where the harness flexes and where any previous work - a stereo, a seat, an alarm - has disturbed it, and see whether moving the loom by hand changes the reading.
- Shorted switch contacts. Once the switch has worn or been contaminated it can short internally. Disconnect the selector assembly and re-read the fault. VAG treats a short to earth as one condition on these inputs and an open circuit or short to positive as the other, so if the complaint flips to the open/high type with the switch unplugged, the fault is inside the switch; if it stays stubbornly low, the short is in the harness and a new switch would change nothing.
Worth knowing: If a drink went into the gear lever, say so at the outset - a proper clean of the switch often fixes it, whereas a workshop with no history may quote for a complete selector assembly. And disconnecting the switch to see whether the fault flips from 'low' to the open/high type takes minutes and tells you immediately whether the switch or the wiring is the problem. If you are going under the console yourself, note that many VAG models run airbag and seatbelt-pretensioner wiring through that area: disconnect the battery and observe the manufacturer's waiting time before disturbing anything with a yellow connector.
Reading the code is the easy part
A code names the circuit that complained. What tells you why is watching the sensor behind it while the engine runs — and that is where a code reader stops and a diagnostic tool starts.
VAGPULSE reads every module in a VW, Audi, Skoda or SEAT — not just the engine — shows the live measuring blocks behind this fault, gives you the freeze-frame conditions it was logged under, and clears it once you have fixed it. It also does what a generic OBD reader cannot on a VAG: service resets, coding, adaptations, and Stage 1–3 flashing with your original file saved first.
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Common questions
What does P071B mean?
P071B means Transmission Mode Switch A Circuit Low. The voltage on this circuit is sitting near zero. Typically a short to earth, or a sensor that has failed to its low end.
Can I drive with P071B?
The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.