P1706

What Does Code P1706 Mean?

DTC P1706 signifies “High Vehicle Speed Observed in Park.” This diagnostic trouble code is registered by the Powertrain Control Module (PCM) when it detects a logical inconsistency between two critical inputs: the Vehicle Speed Sensor (VSS) signal and the Transmission Range (TR) sensor (often integrated into the Park/Neutral safety switch). Specifically, the PCM monitors the VSS signal, which converts rotational speed of the transmission output shaft or wheel speed into an electrical signal indicating vehicle velocity. Concurrently, the PCM monitors the TR sensor, which communicates the current gear selector position (e.g., Park, Reverse, Neutral, Drive, Low). P1706 is set when the PCM receives a VSS input indicating a vehicle speed above a manufacturer-defined threshold (typically 3-10 mph) while simultaneously receiving an input from the TR sensor indicating that the transmission is engaged in the “Park” position. This contradictory data triggers the fault, indicating a potential sensor malfunction, wiring fault, or, in rare cases, an internal PCM processing error. The PCM’s detection logic is designed to prevent unintended vehicle movement or transmission damage, as a vehicle should not be indicating significant speed while the transmission is commanded into Park.

Common Symptoms

• Check Engine Light (CEL) Illumination: The most common and direct symptom, alerting the driver to a detected fault.
• Erratic or Harsh Transmission Shifting: The PCM may enter a “limp mode” or apply incorrect shift strategies due to unreliable speed or gear position data.
• Inaccurate Speedometer/Odometer Readings: If the VSS is at fault, speed display can be incorrect or intermittent.
• Cruise Control Inoperability: Many systems disable cruise control functionality when critical speed or transmission range data is deemed unreliable.
• No-Start Condition (intermittent): If the TR sensor incorrectly reports “Park” when the vehicle is in another gear, or if there’s a serious electrical conflict, the engine may not crank.
• Delayed Engagement or No Engagement of Park: Though less common, if the TR sensor mechanically misaligns or electrically malfunctions, the actual park engagement may not match the reported state.

What Causes the Code P1706?

• Faulty Vehicle Speed Sensor (VSS): An intermittently or continuously erroneous high signal from the VSS, suggesting movement when none is occurring, or sending a signal even at a standstill. This can be due to internal sensor failure, corrosion, or damage.
• Faulty Transmission Range (TR) Sensor (Park/Neutral Safety Switch): A malfunction where the TR sensor incorrectly signals “Park” to the PCM, even when the shifter is in another position or when the vehicle is moving. This could be due to internal switch failure, wear, or physical misalignment.
• Wiring Harness Issues:
  • Short to Voltage: A short circuit in the VSS signal wire to a power source, leading the PCM to misinterpret a high speed signal.
  • Short to Ground: A short in the TR sensor circuit, causing an incorrect “Park” signal.
  • Open Circuit: An interruption in the VSS or TR sensor signal wire, leading to erratic or default values.
  • Chafed or Damaged Wiring: Physical damage to the wiring insulation leading to intermittent shorts or opens, often near the transmission or engine bay.
  • Corroded Connectors: Oxidation or damage to the electrical connectors for either sensor, creating high resistance or intermittent signal loss.
• Powertrain Control Module (PCM) Malfunction: While less common, an internal fault within the PCM itself could lead to misinterpretation of sensor signals or incorrect processing, setting the code erroneously. This should be considered after all other possibilities have been thoroughly investigated.
• Shifter Linkage Misalignment/Damage: Physical issues with the transmission shifter linkage preventing the TR sensor from accurately reflecting the true gear position, leading to a discrepancy.

How to Diagnose and Troubleshoot

A systematic approach is crucial for diagnosing P1706. Begin with an OBD-II scan tool and a digital multimeter (DMM).

1. Retrieve and Analyze Freeze Frame Data: Connect an OBD-II scanner and retrieve DTC P1706. Crucially, examine the freeze frame data associated with the code. Note the vehicle speed, engine RPM, transmission range sensor status, and other parameters when the fault occurred. This information is vital for understanding the conditions under which the PCM detected the anomaly.
2. Check for Related Codes: Look for any other accompanying DTCs, especially those related to VSS (e.g., P0500, P0501, P0502, P0503) or Transmission Range Sensor faults (e.g., P0705, P0706, P0707, P0708), as these can provide further clues.
3. Visual Inspection:
   • Inspect the wiring harnesses and connectors leading to both the VSS and the TR sensor. Look for signs of chafing, fraying, cuts, corrosion, or loose connections. Pay close attention to areas where harnesses pass near exhaust components or sharp edges.
   • Verify the physical mounting and condition of both the VSS and TR sensor for damage or looseness.
   • Check the transmission shifter linkage for any obvious signs of damage or misalignment.
4. Verify VSS Operation:
   • Live Data Scan: With the vehicle safely raised on jack stands (or driven slowly if conditions allow and it’s safe), monitor the “Vehicle Speed Sensor” (VSS) or “Output Shaft Speed Sensor” (OSS) PID on your scan tool’s live data stream. Rotate the drive wheels by hand or use the engine (briefly and cautiously, only if safe to do so) to check if the speed reading changes smoothly and accurately. A high VSS reading at 0 mph (in Park) would strongly indicate a faulty VSS or a short to voltage in its circuit.
   • DMM Measurement (if applicable): For VSS sensors that produce an AC voltage signal (common on older designs), disconnect the sensor and use a DMM set to AC voltage. Rotate the wheel or shaft slowly by hand; you should observe a fluctuating AC voltage. The frequency and voltage should increase with speed. Refer to service information for expected values. For digital VSS signals, an oscilloscope may be required for precise waveform analysis.
5. Verify TR Sensor (Park/Neutral Switch) Operation:
   • Live Data Scan: Monitor the “Transmission Range” or “Gear Selector Position” PID on the scan tool’s live data. Cycle the gear shifter through all positions (P, R, N, D, L) and confirm that the PCM’s reported gear matches the actual selected position on the display. Pay particular attention to the “Park” position. If the sensor reports “Park” when the shifter is in another position, or if it doesn’t correctly register “Park” when selected, the sensor or its linkage is suspect.
   • DMM Measurement: Disconnect the TR sensor connector. Using a DMM set to continuity or resistance mode, probe the relevant terminals (refer to the vehicle’s wiring diagram for pinouts). Cycle the shifter through all positions. Verify that the continuity or resistance changes according to the manufacturer’s specifications for each gear, particularly “Park.” A faulty switch may show open or short circuits in incorrect positions.
6. Circuit Integrity Test: If the sensors appear to function correctly, perform continuity and resistance checks on the wiring harnesses between the VSS/TR sensor connectors and the PCM connector. Disconnect both ends of the harness sections to be tested. Check for:
   • Open Circuits: Use a DMM to test for continuity. Resistance should be very low (typically < 5 ohms).
   • Shorts to Ground: Test continuity between each wire and a known good chassis ground. There should be no continuity.
   • Shorts to Power: With the ignition ON and components disconnected, test for voltage on signal wires that should only have ground or sensor-specific voltage.
7. PCM Diagnosis: Only after thoroughly verifying both sensors and all associated wiring circuits, and if the issue persists, should a PCM malfunction be considered. This typically requires specialized diagnostic tools and expertise.

Recommended Repairs and Solutions

Repairs for P1706 are directly dependent on the root cause identified during diagnosis:

• Replace Faulty Vehicle Speed Sensor (VSS): If diagnostic steps confirm the VSS is sending an erroneous high signal or is otherwise malfunctioning, replace the sensor. Ensure the new sensor is of OEM quality or a reputable aftermarket equivalent. Clear DTCs and perform a road test to verify the repair.
• Replace Faulty Transmission Range (TR) Sensor (Park/Neutral Safety Switch): If the TR sensor is found to be providing inaccurate gear position data, especially for the “Park” position, it should be replaced. After replacement, ensure proper alignment if applicable, clear codes, and test thoroughly.
• Repair or Replace Damaged Wiring/Connectors: Any identified shorts, opens, chafed wires, or corroded connectors in the VSS or TR sensor circuits must be repaired or replaced. Use appropriate automotive-grade wire and connectors, ensuring secure, weather-sealed connections.
• Adjust Shifter Linkage: If the TR sensor itself is functional but misaligned due to worn or improperly adjusted shifter linkage, adjust or repair the linkage according to manufacturer specifications. This ensures the TR sensor accurately reflects the driver’s selected gear.
• PCM Replacement/Reprogramming: If all other components and wiring have been meticulously tested and confirmed to be in good working order, and the problem persists, a PCM fault may be indicated. PCM replacement often requires programming specific to the vehicle’s VIN. This should be considered a last resort due to cost and complexity.

Mechanic’s Tip: Always clear the DTCs after performing a repair. Then, perform a road test under varying conditions that would typically trigger the code (if safely possible) or allow the vehicle’s monitors to complete their drive cycles to confirm the repair. Intermittent issues can be particularly challenging, so a thorough wiggle test of wiring harnesses while monitoring live data can sometimes reveal the problem.