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DTC codes / GM codes / P1815

P1815 · GMTransmission Range Switch Start In Wrong Range

P1815 on GM vehicles means the transmission control module (TCM) has detected that the transmission range switch, also called the park/neutral position switch, is reporting a gear range that does not match the range the driver has selected or the range the TCM expects during start-up. The computer sees the switch telling it the transmission is in a different range than it should be when the engine is being started, which can prevent cranking or cause harsh engagement.

SystemPowertrain
Code typeGM specific
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • The engine may not crank or start in Park or Neutral, or may only start in one of those positions.
  • The gear indicator on the instrument cluster may be blank, flashing, or show the wrong range.
  • The transmission may engage harshly or hesitate when shifting from Park to Drive or Reverse.
  • The reverse lights may not illuminate when Reverse is selected.
  • Often no symptoms besides the warning light, especially if the misreport is intermittent.
  • The vehicle may enter limp mode or set related transmission codes.

Common causes, most likely first

  1. Faulty or misadjusted transmission range switch (park/neutral position switch).
  2. Corroded, loose, or damaged wiring or connector at the range switch.
  3. Improper adjustment of the switch linkage or cable.
  4. Internal transmission mechanical issue causing the manual valve to not match the switch position.
  5. Failed transmission control module (TCM) or ignition switch circuit issue.
  6. Aftermarket or incorrect range switch installation.

How to diagnose and fix it

  1. Verify the battery is fully charged and connections are clean, as low voltage can cause false range switch codes.
  2. Check for other stored codes in the TCM and body control module (BCM) to see if the range signal is used by multiple modules.
  3. Inspect the range switch connector and wiring for corrosion, chafing, or loose pins; repair as needed.
  4. Perform a range switch adjustment according to GM service information, ensuring the switch aligns with the detents in the transmission.
  5. Backprobe the range switch circuits and compare the switch logic to the TCM data to confirm the switch is reporting correctly.
  6. If the switch fails electrical testing, replace the transmission range switch and recheck operation.
  7. If the switch and wiring are good, diagnose the TCM and ignition switch circuits, including the starter enable circuit.

Range Switch Adjustment Before Replacement

  • Many P1815 codes are set simply because the range switch is slightly out of adjustment after transmission work or linkage wear, not because the switch itself has failed.
  • The range switch on many GM transmissions also controls reverse lights and starter enable, so a no-crank condition with P1815 often points to the switch rather than the starter.
  • A scan tool that shows transmission range switch data in real time is far more useful than a simple code reader, because you can watch the switch states change as you move the shifter.
  • Corrosion inside the range switch connector is a common cause that is missed when only the switch is replaced; always inspect the harness side.
  • P1815 can be set by a weak battery or poor ground, so check voltage drops before condemning the switch.

Can I keep driving with P1815?

If the vehicle starts and drives normally, you can drive it to a repair shop, but avoid relying on remote start or assuming the gear indicator is accurate. If the engine will not crank or the transmission engages harshly, do not continue driving and have it diagnosed promptly.

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 GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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