Code
P1705
GMC
P — Powertrain
P/N Signal Output Circuit
AI status
Completed
Completed
100%
Causes
- Faulty park/neutral (P/N) or transmission range switch
- Open, shorted, or corroded wiring or connector between P/N switch and PCM
- Poor or missing ground at switch or PCM
- Blown fuse or power supply problem to the switch or PCM reference
- Intermittent connector contact due to corrosion, bent pins, or water intrusion
- PCM input circuit fault or internal failure
Symptoms
- Check Engine Light (MIL) illuminated
- Vehicle may not crank because PCM does not detect Park or Neutral (no‑start in Park)
- Transmission may fail to shift properly or enter limp/limited mode
- PRNDL indicator may be incorrect or not change with gear selection
- Intermittent start or shifting behavior dependent on shifter position/movement
What to check
- Retrieve freeze frame data and full DTC list from the PCM and note conditions when P1705 set
- Visually inspect P/N switch, wiring harness, connectors, and grounds for damage, corrosion, pin push‑outs, or water intrusion
- Check fuses and power feeds related to transmission range/P/N circuit and PCM power/ground
- Backprobe the P/N switch connector with connector connected and ignition ON to observe signal behavior while moving the shifter through all positions
- Perform continuity and resistance checks between the P/N switch terminals and the PCM connector with battery disconnected
- Wiggle test wiring while monitoring the signal to reproduce intermittent faults
Signal parameters
- Reference/logic voltage: typically a stable reference (approx. 5 V) or switched battery voltage depending on vehicle — verify with OEM data
- Expected signal behavior: signal should change state only at defined gear positions (Park/Neutral vs. other gears); for many systems the P/N circuit is low (near 0 V) in one state and high (~5 V or battery voltage) in the other — confirm with manufacturer specifications
- Connector resistance: low continuity between switch terminal and PCM terminal (near 0 Ω) when tested for continuity; open circuit when disconnected in other positions as specified by OEM
Diagnostic algorithm
- Connect scan tool, read freeze frame and live data for PRNDL/park‑neutral status while cycling the shifter. Note when fault sets.
- Perform a visual inspection of the P/N switch, shifter linkage, harness routing, and connectors. Repair any obvious damage or corrosion.
- Verify fuses and related power/ground circuits for the transmission range switch and PCM.
- Backprobe the P/N switch connector with key ON (engine off) and observe voltage at each gear position. Compare to expected values from OEM data. Look for unstable or missing signal.
- With battery disconnected, perform continuity/resistance check between the switch terminals and the PCM connector to verify no opens/shorts. Check for shorts to ground and battery.
- Wiggle the harness and shift linkage while monitoring live signal to attempt to reproduce the fault.
- If the switch and wiring check good, disconnect switch and inspect connector pins; replace or repair connector/wiring as needed.
- If wiring and switch replacement do not clear the code, perform PCM input circuit testing per service manual. Replace PCM only after confirming external wiring and switch are good.
- Clear codes and test drive; verify P1705 does not return and that PRNDL behavior is correct.
Likely causes
- Damaged or corroded connector/wiring at the P/N switch
- Failed P/N (range) switch
- Poor ground or blown fuse supplying the switch
- Intermittent wiring short to power or ground when shifter is moved
- PCM input fault (less common)
Fault status
Status
P1705 — P/N Signal Output Circuit: PCM has detected an invalid, missing, or intermittent park/neutral (range) switch signal. May prevent starting or cause transmission shift/limp behavior. Inspect switch, wiring, connectors, fuses, and PCM inputs.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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