Complete Guide to Transmission Error Code P1706: Diagnosis, Repair, and Prevention
Understanding Error Code P1706
Technical Definition
P1706 is an OBD-II diagnostic trouble code indicating “Transmission Range Sensor Circuit Low.” This sensor, also known as the Transmission Range Sensor (TRS) or Neutral Safety Switch, communicates the gear selector position (Park, Reverse, Neutral, Drive) to the vehicle’s Transmission Control Module (TCM) and Powertrain Control Module (PCM). A “Circuit Low” signal means the TCM/PCM is receiving voltage below the expected operating range, typically below 0.5 volts when it should read between 0.5-4.5 volts depending on gear position.
Primary Functions of the Transmission Range Sensor
| Function | Description | Vehicle Systems Affected |
|---|---|---|
| Gear Position Detection | Determines shifter position and communicates to TCM | Transmission Control, Gear Selection |
| Starter Interlock | Prevents engine start unless in Park or Neutral | Starting System, Safety System |
| Reverse Light Activation | Activates backup lights when in Reverse | Lighting System, Safety |
| Transmission Strategy | Informs shift patterns and torque converter lockup | Fuel Economy, Performance |
Symptoms and Diagnostic Procedures
Common Symptoms of P1706
- No-start condition (engine cranks but doesn’t start, or doesn’t crank at all)
- Erratic shifting or transmission stuck in one gear (limp mode)
- Incorrect gear display on dashboard (shows wrong gear)
- Reverse lights not working or staying on continuously
- Check Engine Light illuminated (often with reduced power mode)
- Vehicle starts in gear without brake pedal depressed (serious safety issue)
Diagnostic Step-by-Step Procedure
| Step | Procedure | Tools Needed | Expected Result |
|---|---|---|---|
| 1. Preliminary Check | Verify transmission fluid level and condition | Dipstick, Flashlight | Clean fluid at proper level |
| 2. Code Scan | Read and record all codes with OBD-II scanner | Professional Scanner | P1706 and any related codes |
| 3. Visual Inspection | Check wiring harness and connectors for damage | Inspection Mirror | Intact wiring, clean connections |
| 4. Voltage Test | Test sensor reference voltage and ground circuits | Multimeter, Wiring Diagram | 5V reference, solid ground |
| 5. Sensor Test | Measure resistance across sensor terminals | Ohmmeter, Service Manual | Resistance within spec (varies by make) |
| 6. Signal Test | Monitor signal voltage while moving shifter | Oscilloscope or Scanner | Smooth voltage transition between gears |
Voltage Specifications by Manufacturer
| Gear Position | Ford Specification | GM Specification | Toyota Specification | Honda Specification |
|---|---|---|---|---|
| Park (P) | 3.8-4.2V | 0.5-1.0V | 4.0-4.5V | 3.9-4.4V |
| Reverse (R) | 2.8-3.2V | 2.0-2.5V | 3.0-3.5V | 2.9-3.4V |
| Neutral (N) | 1.8-2.2V | 3.0-3.5V | 2.0-2.5V | 1.9-2.4V |
| Drive (D) | 0.8-1.2V | 4.0-4.5V | 1.0-1.5V | 0.9-1.4V |
| Acceptable Range | ±0.2V from spec | ±0.25V from spec | ±0.15V from spec | ±0.2V from spec |
Repair Procedures and Cost Analysis
Common Causes of P1706 Code
| Cause | Frequency | Repair Complexity | Estimated Parts Cost |
|---|---|---|---|
| Faulty Transmission Range Sensor | 45% of cases | Medium | $85-$220 |
| Damaged Wiring Harness | 30% of cases | Low-Medium | $25-$150 |
| Corroded Connectors | 15% of cases | Low | $10-$50 |
| Low Transmission Fluid | 5% of cases | Low | $20-$60 |
| Faulty TCM/PCM | 5% of cases | High | $300-$800+ |
Repair Time Estimates
Related Error Codes and Differential Diagnosis
Commonly Associated Codes
| Error Code | Description | Relation to P1706 | Action Required |
|---|---|---|---|
| P0705 | Transmission Range Sensor Circuit Malfunction | General TRS circuit issue | Complete circuit diagnosis |
| P0706 | Transmission Range Sensor Performance | Sensor out of range | Test sensor output |
| P0707 | Transmission Range Sensor Circuit Low | Similar to P1706 (manufacturer specific) | Same as P1706 diagnosis |
| P0708 | Transmission Range Sensor Circuit High | Opposite condition | Check for short to power |
| P1705 | Transmission Range Sensor Circuit Intermittent | Intermittent connection | Check for loose connections |
Frequently Asked Questions
Not recommended. While some vehicles may operate in limp mode, driving with P1706 can lead to:
- Unexpected vehicle movement if it starts in gear
- Transmission damage from incorrect shifting
- Safety hazards (no reverse lights, starter interlock failure)
- Potential stranding if condition worsens
Towing to a repair facility is the safest option.
Repair costs vary significantly:
| DIY Sensor Replacement | $90-$250 (parts only) |
| Professional Repair (Sensor) | $250-$500 total |
| Wiring Repair | $150-$350 total |
| Dealer Diagnosis & Repair | $300-$700+ |
Most independent shops charge 1-2 hours labor plus parts.
Both codes relate to Transmission Range Sensor issues but indicate different problems:
- P1706: “Circuit Low” – Voltage signal is below expected range (typically below 0.5V)
- P0706: “Performance” – Sensor reading is implausible or out of range, but not necessarily low voltage
P1706 usually indicates a short to ground or faulty sensor, while P0706 could indicate mechanical binding, sensor wear, or alignment issues.
Yes, in some cases. Severely low transmission fluid can affect hydraulic pressure, causing the manual valve (connected to TRS) to not fully engage positions. This creates false sensor readings. Always check fluid level first – it’s the easiest and least expensive potential fix. However, low fluid alone only causes P1706 in about 5% of cases.
