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DTC codes / P07xx · Transmission / P071F

P071FTransmission Mode Switch B Circuit High

P071F means the transmission control module (TCM) has detected an abnormally high voltage on the circuit for Transmission Mode Switch B, which is a driver-selectable input such as a sport, tow/haul, or manual shift mode button. The TCM expects the signal voltage to stay within a calibrated range, and a reading above that range indicates an open circuit, a short to voltage, or a faulty switch.

SystemPowertrain
Code typeGeneric (all makes)
SeverityLow
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • The check engine light or transmission warning light illuminates on the dashboard.
  • Often no symptoms besides the warning light, with normal shifting and driveability.
  • The selected driving mode (sport, tow/haul, or manual) may not engage or may default to normal mode.
  • The mode indicator lamp on the switch or instrument cluster may fail to light or stay lit incorrectly.
  • In some vehicles, the transmission may default to a limp-home mode with firm or delayed shifts.
  • Other mode-related features, such as grade braking or manual gear holding, may become unavailable.

Common causes, most likely first

  1. A faulty transmission mode switch B that internally shorts to voltage or has excessive resistance.
  2. An open or damaged wire in the mode switch B signal circuit, often from chafing or a broken connector pin.
  3. A short to voltage on the signal circuit, such as from a rubbed wire touching a power wire.
  4. Corrosion or water intrusion at the switch connector or at the TCM harness connector.
  5. A poor ground connection for the switch or for the TCM, causing reference voltage to float high.
  6. A failed TCM that incorrectly reads the switch input voltage.
  7. Aftermarket accessories or wiring repairs that backfeed voltage onto the mode switch circuit.

How to diagnose and fix it

  1. Connect a scan tool and read all transmission control module codes and live data to confirm P071F is current and see what voltage the TCM reports for mode switch B.
  2. Inspect the mode switch connector and the TCM connector for corrosion, loose pins, or water intrusion, and clean or repair as needed.
  3. Check the switch ground circuit for excessive resistance using a multimeter, and repair any bad ground.
  4. Measure voltage on the mode switch B signal circuit at the switch with the key on, comparing it to the manufacturer's specification for each switch position.
  5. Disconnect the switch and check for an open or short to voltage on the signal wire between the switch and the TCM, repairing the harness as required.
  6. Test the mode switch itself with a multimeter for continuity or resistance in each position, and replace it if it does not match specifications.
  7. Clear the codes and road test the vehicle through all mode selections to verify the repair and confirm the code does not return.

What a high voltage reading really means

  • A high voltage on a switch input circuit usually points to an open circuit or a short to voltage rather than a failed switch, so testing the wiring before replacing parts saves time and money.
  • Many mode switches are simple momentary buttons that share a common return wire, so a fault in one switch can affect the voltage seen on another mode circuit and set related codes.
  • The TCM may set P071F intermittently if the switch is only faulty when cold or when the steering column or console is moved, so wiggle-testing the harness while watching live data is a valuable step.
  • Aftermarket remote starters, alarms, or phone chargers plugged into the accessory socket can backfeed voltage onto shared circuits and cause false high-voltage readings on switch inputs.
  • Some vehicles use a single wire with different resistor values for multiple mode functions, so a poor connection can shift the voltage high and set this code even though the switch contacts are clean.

Can I keep driving with P071F?

The vehicle is generally safe to drive with P071F because the transmission usually defaults to a normal mode, but avoid relying on sport, tow/haul, or manual mode features until the fault is repaired. If the transmission enters a limp-home mode with harsh shifting, have it diagnosed promptly to prevent further driveability issues.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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