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DTC codes / P07xx · Transmission / P071E

P071ETransmission Mode Switch B Circuit Low

P071E means the transmission control module (TCM) has detected an abnormally low voltage on the signal circuit for Transmission Mode Switch B, a driver-selectable input such as a sport, tow/haul, or manual shift mode button. The TCM expects a specific voltage range when the switch is in its normal state and another when pressed, and a low reading tells it the circuit is shorted to ground, the switch is stuck closed, or the wiring has failed.

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.
  • The mode selection button or switch does not change transmission behavior when pressed.
  • The transmission stays in a single default mode, often normal or economy, regardless of button input.
  • Harsh or delayed shifts may occur because the TCM cannot confirm the selected driving mode.
  • The instrument cluster may show an incorrect or blank mode indicator.
  • Often no symptoms besides the warning light, especially if the default mode is acceptable to the driver.

Common causes, most likely first

  1. A faulty transmission mode switch that is internally shorted to ground and holds the signal low.
  2. Damaged or chafed wiring between the switch and the TCM, shorting the signal circuit to ground.
  3. Corroded or loose electrical connector pins at the switch or TCM, creating a low-resistance path.
  4. Water intrusion into the switch or connector, causing a conductive short across the signal circuit.
  5. A defective TCM with an internal pull-up resistor failure or signal processing fault.
  6. Aftermarket accessories or poor previous repairs tapping into the mode switch circuit and pulling it low.

How to diagnose and fix it

  1. Scan all modules and record freeze-frame data for P071E to confirm when the low signal was detected.
  2. Inspect the mode switch connector and TCM connector for corrosion, water intrusion, bent pins, or loose terminals.
  3. Disconnect the switch and measure resistance across its terminals in both the normal and pressed states, comparing to specifications.
  4. With the switch disconnected, check the signal wire from the switch to the TCM for continuity to ground; any continuity indicates a short.
  5. Wiggle-test the harness while monitoring live mode switch voltage on a scan tool to expose an intermittent short.
  6. If the circuit tests good, substitute a known-good switch or use a scan tool to command the mode input and verify TCM response.
  7. Repair or replace the faulty switch, harness section, or TCM as indicated by the test results, then clear the code and verify the mode function.

Mode switch shorts hide in the harness

  • A mode switch that feels fine mechanically can still be electrically shorted internally, so resistance testing in both states is essential before condemning the TCM.
  • The signal circuit often runs through a door sill or console area where chafing against a bracket is common, and a single worn spot can pull the voltage low only on bumps.
  • Some vehicles use a multiplexed resistor ladder for several mode buttons, so one shorted button can make the TCM misread other button presses as well.
  • A low signal code does not always mean the switch is bad; a poor ground at the switch housing can create the same low-voltage reading.
  • Aftermarket remote starters or alarm installers frequently tap the mode switch wire, leaving a partial short that sets P071E intermittently.

Can I keep driving with P071E?

The vehicle remains safe to drive because the transmission defaults to a normal mode, but avoid relying on the mode button until the fault is repaired. If shifting becomes harsh or the transmission enters limp mode, have it diagnosed promptly.

Tools that help

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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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