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DTC codes / GM codes / P1705

P1705 · GMP/N Signal Output Circuit

P1705 on a GM vehicle indicates that the powertrain control module (PCM) has detected an unexpected voltage condition on the park/neutral (P/N) signal output circuit, which it uses to confirm the transmission is in Park or Neutral for safe starting and idle strategy. The PCM monitors this output circuit for continuity and expected voltage levels, and it sets the code when the signal does not match the commanded state or falls outside the valid range.

SystemPowertrain
Code typeGM specific
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • The engine may not crank or start because the PCM does not recognize Park or Neutral, interrupting the starter enable signal.
  • The gear position indicator on the instrument cluster may be blank, flashing, or show the wrong range.
  • The engine may idle poorly or stall when coming to a stop because idle speed strategy is based on the P/N signal.
  • The transmission may shift harshly or fail to enter certain modes that depend on the P/N input.
  • Often no symptoms besides the warning light, especially if the fault is intermittent or only affects a redundant signal path.
  • The vehicle may refuse to shift out of Park or may allow the key to be removed in a gear other than Park.

Common causes, most likely first

  1. A faulty park/neutral position switch (also called the transmission range sensor) that fails to output the correct signal.
  2. Damaged, corroded, or chafed wiring in the P/N signal output circuit between the switch and the PCM.
  3. A poor ground connection at the switch, chassis, or PCM that skews the output voltage.
  4. A failed PCM driver or internal circuit on the P/N output channel, though this is less common.
  5. Water intrusion or debris in the switch connector causing intermittent opens or shorts.
  6. Aftermarket alarm or remote start wiring that taps into the P/N signal and introduces a fault.

How to diagnose and fix it

  1. Scan all modules for related codes and record freeze-frame data to see the conditions when P1705 set.
  2. Inspect the park/neutral switch connector and the PCM connector for corrosion, pushed pins, or loose terminals.
  3. Check the P/N signal output circuit for continuity, short to ground, and short to voltage using a digital multimeter.
  4. Verify the park/neutral switch operation by monitoring the P/N signal status on a scan tool while moving the shifter through all ranges.
  5. Test the switch output voltage at the PCM connector while wiggling the harness to catch intermittent faults.
  6. If the circuit and switch test good, perform a resistance and voltage drop test on the switch ground circuit.
  7. Replace the park/neutral position switch only after confirming the circuit is sound, then clear codes and verify the P/N signal reads correctly in all gear positions.

What the P/N output circuit really does

  • The P/N signal output is not just for the starter; the PCM uses it to command idle speed, fuel cut on deceleration, and certain transmission line pressure strategies, so a fault can cause drivability complaints that seem unrelated to gear selection.
  • A common misdiagnosis is replacing the park/neutral switch when the real problem is a corroded ground wire at the transmission case, which offsets the output voltage just enough to set P1705 without killing the starter circuit.
  • Aftermarket remote start or alarm systems that splice into the P/N wire often cause this code because the added load or backfeed confuses the PCM's output monitoring circuit.
  • On some GM models, the P/N signal is shared with the body control module (BCM) for key-in-ignition and door chime logic, so a BCM fault or a shorted BCM input can pull the circuit down and set P1705 even though the switch is fine.
  • The code can set intermittently from vibration or temperature changes, so a static resistance check may pass; a wiggle test and a scan tool graph of the P/N signal while driving over bumps are often needed to expose the fault.

Can I keep driving with P1705?

You can usually drive the vehicle if it starts and moves, but avoid relying on remote start or leaving it in gear without the parking brake, and do not ignore a no-crank condition because the fault can leave you stranded. Have the circuit inspected soon, especially if the engine cranks intermittently or the gear indicator acts erratically.

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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