Code
P1705
HUMMER
P — Powertrain
P/N Signal Output Circuit
AI status
Completed
Completed
100%
Causes
- Open circuit in P/N signal wire(s)
- Short to ground or short to battery (VB) on P/N signal circuit
- Corroded or damaged connector at park/neutral switch or PCM/TCM
- Failed park/neutral position (PNP) or transmission range switch
- Poor or missing engine/chassis ground related to the circuit
- Intermittent wiring fault (chafing, broken strand)
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Vehicle may not crank in Park/Neutral or has no-start in Park/Neutral (safety interlock)
- Incorrect or no gear indicator (dash PRNDL)
- Transmission may not shift properly or may enter limp mode
- Starter engages only in Neutral or only in Park, or not at all depending on circuit status
- Possible inability to shift out of Park (shift interlock issues)
What to check
- Read stored freeze frame and pending codes with a scan tool; note related transmission codes
- Obtain vehicle wiring diagram and pinouts for P/N switch and PCM/TCM
- Visually inspect P/N switch connector and harness for corrosion, damage, or pin issues
- Backprobe P/N switch connector and PCM/TCM pin with ignition ON to verify reference voltage and signal
- Check for continuity and shorts between P/N switch and module with ignition OFF (multimeter)
- Wiggle harness while monitoring signal to reproduce intermittent faults
Signal parameters
- Reference voltage (if used): typically ~5 V (check vehicle-specific wiring diagram)
- Signal voltage: switches typically output a low (~0–0.5 V) or high (~4–5 V) depending on position — P and N positions should produce the expected voltage states per wiring diagram
- Continuity between switch terminal and PCM input: near 0 ohms when connected (with ignition OFF and connectors disconnected)
- Open-circuit: infinite resistance; short-to-ground: near 0 ohms between signal and chassis ground
Diagnostic algorithm
- Verify code and retrieve freeze frame/pending codes with a scan tool; record vehicle conditions.
- Review wiring diagram/pinout for the P/N (park/neutral) output circuit and identify reference, signal, and ground pins at the switch and PCM/TCM.
- Visually inspect connectors and wiring from transmission P/N switch to module for damage, corrosion, or loose pins; repair as needed.
- With ignition ON (engine off), backprobe the P/N switch connector: verify reference voltage (if applicable) and monitor signal voltage while moving gear selector to Park and Neutral. Compare readings to manufacturer values.
- With ignition OFF, disconnect connectors and measure continuity/resistance between the P/N switch signal pin and PCM input pin. Check for short to ground or battery by measuring resistance to ground and to battery voltage circuit.
- Wiggle the harness and connectors while monitoring the signal to detect intermittent faults.
- If wiring and connectors test good and switch does not produce expected outputs, replace the park/neutral (range) switch per service procedure.
- If replaced switch still fails or wiring short/open is not found, test or substitute the PCM/TCM if supported by service info and after all wiring/switch checks pass.
- Clear codes, perform a self-test and a road test to confirm repair; re-scan for return of code.
Likely causes
- Connector corrosion or bent pins at the P/N switch or module
- Broken or chafed wire between P/N switch and PCM/TCM
- Failed park/neutral (range) switch on the transmission
- Missing reference voltage or ground at the switch due to poor connections
Fault status
Status
P1705 — Park/Neutral signal output circuit fault. The PCM/TCM is detecting an abnormal or missing P/N output signal. Inspect wiring, connectors, park/neutral (range) switch, and module inputs.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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