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DTC codes / P08xx · Transmission / P0815

P0815Upshift Switch Circuit

P0815 indicates that the transmission control module (TCM) has detected an abnormal condition in the upshift switch circuit, which is part of the manual shift control system on automatic transmissions. The TCM monitors the voltage or signal from the upshift switch and sets this code when the signal is out of range, stuck, or inconsistent with expected operation.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • The malfunction indicator lamp (MIL) illuminates on the dashboard.
  • The transmission may not respond to manual upshift commands, leaving the driver unable to select a higher gear.
  • The transmission may default to a limp mode, limiting gear selection to a single gear or a reduced set.
  • The driver may notice harsh or delayed shifts as the TCM substitutes default shift logic.
  • In some vehicles, the manual shift mode indicator may flash or display an error message.
  • Often no symptoms besides the warning light, especially if the switch is only intermittently faulty.

Common causes, most likely first

  1. Faulty upshift switch, such as worn contacts or internal failure.
  2. Damaged or corroded wiring in the upshift switch circuit, including opens or shorts.
  3. Loose or corroded electrical connector at the switch or TCM.
  4. Transmission control module (TCM) software glitch or internal fault.
  5. Mechanical binding or misalignment of the shift lever assembly affecting switch operation.
  6. Contamination or debris interfering with the switch mechanism.

How to diagnose and fix it

  1. Verify the code with a scan tool and check for any related codes in the transmission control module.
  2. Inspect the upshift switch and its connector for physical damage, corrosion, or loose pins.
  3. Test the upshift switch operation using a multimeter to check for continuity or voltage changes when the switch is activated.
  4. Check the wiring harness between the switch and the TCM for opens, shorts, or chafing.
  5. If the switch tests faulty, replace the upshift switch and clear the code.
  6. If the wiring and switch are good, check for TCM software updates or perform a relearn procedure as specified by the manufacturer.
  7. If the fault persists, diagnose the TCM and internal transmission components as needed.

Before replacing the upshift switch

  • A loose or corroded connector at the upshift switch is a common cause that is often overlooked, so always inspect and clean the terminals before condemning the switch.
  • The upshift switch circuit can be affected by aftermarket accessories or poor ground connections, so check for any recent electrical work or added devices.
  • In some vehicles, the upshift switch is integrated into the shift lever assembly, and a mechanical problem with the lever can mimic a switch failure.
  • A faulty brake pedal switch or other input can sometimes set related codes that affect manual shift operation, so scan all modules for stored codes.
  • The TCM may set P0815 intermittently if the switch signal is erratic, so a wiggle test of the harness while monitoring live data can reveal intermittent faults.

Can I keep driving with P0815?

If the vehicle drives normally and only the warning light is on, you can drive cautiously to a repair shop, but avoid using the manual shift feature. If the transmission is stuck in limp mode or shifts erratically, limit driving to a short distance and seek professional diagnosis to prevent further damage.

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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