P0708 Code: Complete Diagnostic & Repair Guide
Everything you need to know about diagnosing and fixing Transmission Range Sensor Circuit High Input issues
What is P0708 Code?
The P0708 diagnostic trouble code indicates a problem with your vehicle’s Transmission Range Sensor (TRS)Also known as transmission position sensor or neutral safety switch. This sensor communicates the current gear position (Park, Reverse, Neutral, Drive, etc.) to the PCMPowertrain Control Module – the vehicle’s main computer.
When the PCM detects a higher than expected voltage signal from the TRS circuit, it triggers the P0708 code. This typically indicates a short to power in the sensor circuit or an internal sensor failure.
Symptoms of P0708 Code
When your vehicle’s PCM detects a high input signal from the transmission range sensor, you may experience one or more of these symptoms:
| Symptom | Frequency | Severity |
|---|---|---|
| Check Engine Light | Very Common | Medium |
| Incorrect Gear Position Display | Common | Medium |
| Starting Issues | Common | High |
| Transmission Shifting Problems | Common | High |
| Vehicle May Roll in Park | Less Common | Very High |
| Backup Lights Not Working | Common | Low |
| Vehicle Starts in Gear | Less Common | Very High |
Diagnosing P0708 Code: Complete Step-by-Step Guide
Proper diagnosis of a P0708 code requires a systematic approach. Follow these detailed steps to identify the root cause:
Step 1: Initial Assessment and Code Verification
- Connect OBD-II Scanner: Use a professional-grade scanner to confirm the P0708 code and check for any additional related codes (P0700, P0706, P0707, etc.)
- Record Freeze Frame Data: Note the conditions when the code was set (vehicle speed, engine temperature, etc.)
- Clear Codes and Test Drive: Clear the codes and perform a test drive to see if the code returns immediately or under specific conditions
- Monitor Live Data: Access the TRS data PID (Parameter ID) and monitor the sensor readings while moving the shifter through all positions
// Park (P): 0.5-1.0V
// Reverse (R): 1.5-2.0V
// Neutral (N): 2.5-3.0V
// Drive (D): 3.5-4.0V
// 2nd (2): 4.5V
// 1st (1): 5.0V
// Readings consistently above 5V indicate circuit issues
Step 2: Comprehensive Visual Inspection
- Inspect TRS Wiring Harness: Check the entire length of the wiring from the TRS connector to the PCM for:
- Chafing or rubbing against sharp edges
- Burned or melted insulation
- Corrosion at connectors
- Previous repair attempts (splices, tape, etc.)
- Check Connector Condition:
- Look for bent, broken, or corroded pins
- Ensure connector is fully seated and locking mechanism works
- Check for moisture or transmission fluid in the connector
- Verify TRS Mounting:
- Ensure sensor is properly mounted and secure
- Check for physical damage to the sensor housing
- Verify shift linkage is correctly adjusted and moves freely
- Look for Fluid Leaks: Check for transmission fluid leaks that could contaminate the sensor or connector
Step 3: Detailed Electrical Testing
- Reference Voltage Check:
- Disconnect TRS connector with ignition ON, engine OFF
- Using a digital multimeter, check for 5V reference signal at the appropriate pin
- Expected: 4.5-5.5V DC. If incorrect, check PCM and wiring
- Ground Circuit Check:
- Measure resistance between ground pin and known good ground
- Expected: Less than 5 ohms. High resistance indicates poor ground
- Signal Circuit Check:
- Check for short to power in signal circuit
- With connector disconnected, check for voltage on signal wire (should be 0V)
- If voltage present, trace and repair short to power
- Continuity Tests:
- Check continuity of all TRS circuits between sensor connector and PCM
- Repair any open circuits or high resistance connections
Step 4: Component Testing and Replacement
- TRS Resistance Test:
- Consult service manual for specific resistance values for your vehicle
- Measure resistance across TRS terminals in different gear positions
- Compare readings to manufacturer specifications
- TRS Replacement:
- If faulty, replace TRS with OEM or high-quality aftermarket part
- Follow manufacturer procedure for installation
- Some vehicles require adjustment or calibration after replacement
- PCM Testing (if necessary):
- If all circuits test good and sensor is functioning, PCM may be faulty
- This is rare – verify all other possibilities first
- Consult with dealership or specialized repair facility
Step 5: Repair Verification
- Clear Codes: Use scan tool to clear all diagnostic trouble codes
- Test Drive: Perform comprehensive test drive including:
- City driving with frequent stops
- Highway driving at various speeds
- Multiple gear changes and shifting patterns
- Monitor System: Use scan tool to monitor TRS data during test drive
- Final Check: Verify:
- No codes return
- All transmission functions operate correctly
- Gear indicator shows correct position
- Backup lights illuminate in Reverse
Common Causes of P0708 Code
The P0708 code can be triggered by various issues. Here are the most common causes with detailed explanations:
| Cause | Frequency | Repair Complexity | Typical Repair |
|---|---|---|---|
| Faulty Transmission Range Sensor – Internal sensor failure causing incorrect voltage signals | High | Medium | Sensor replacement |
| Wiring Issues – Short to power in signal circuit, damaged wiring harness, or corroded connectors | High | Medium-High | Wire repair, connector replacement |
| Poor Electrical Connections – Loose, corroded, or damaged connectors at TRS or PCM | Medium | Low | Connector cleaning/repair |
| Failed PCM – Rare, but possible internal PCM failure (diagnose everything else first) | Low | High | PCM replacement/programming |
| Incorrectly Adjusted Shift Linkage – Mechanical misalignment causing sensor misreading | Medium | Low-Medium | Linkage adjustment |
| Transmission Fluid Contamination – Fluid leaks contaminating sensor or connector | Low | High | Sensor replacement, fluid service |
Repair Costs and Time Estimates
Repair costs for P0708 vary based on the root cause, vehicle make/model, and labor rates in your area. Below are detailed cost estimates:
| Repair | Parts Cost | Labor Cost | Total Estimate | Time Required |
|---|---|---|---|---|
| TRS Replacement (External) | $75 – $250 | $100 – $200 | $175 – $450 | 1-1.5 hours |
| TRS Replacement (Internal) | $150 – $400 | $300 – $600 | $450 – $1000 | 3-5 hours |
| Wiring Repair | $20 – $100 | $100 – $300 | $120 – $400 | 1-3 hours |
| Connector Replacement | $30 – $80 | $80 – $150 | $110 – $230 | 1 hour |
| Shift Linkage Adjustment | $0 – $50 | $50 – $100 | $50 – $150 | 30-60 minutes |
| PCM Replacement | $300 – $1000 | $100 – $200 | $400 – $1200 | 1-2 hours |
| Diagnostic Fee Only | $0 | $80 – $150 | $80 – $150 | 30-60 minutes |
Professional vs DIY Repair Analysis
Whether you should attempt to fix a P0708 code yourself depends on your mechanical skill level, available tools, and the specific cause of the problem:
Parts only + your time
Parts + labor ($80-$150/hour)
Basic hand tools, multimeter, possibly OBD-II scanner
Professional scan tools, oscilloscopes, specialized equipment
Intermediate automotive and electrical skills
Certified technicians with advanced training
2-6 hours (depending on experience)
1-3 hours typically
Higher risk of misdiagnosis or improper repair
Lower risk with warranty on repairs
Parts warranty only (if purchased new)
Parts and labor warranty (typically 12 months/12,000 miles)
Frequently Asked Questions
Limited driving only. While you may be able to drive the vehicle to a repair shop, continued driving with a P0708 code is not recommended. The faulty TRS can cause unexpected transmission behavior, starting issues, and most importantly, safety concerns like the vehicle rolling in “Park” or starting in gear.
High urgency. Due to the potential safety risks and possibility of being stranded, P0708 should be addressed within a few days of discovery. If you experience starting issues or incorrect gear indications, have the vehicle towed to a repair facility.
Yes, potentially. While the code itself doesn’t directly damage the transmission, the resulting incorrect gear signals can lead to harsh shifting, delayed shifts, or transmission operation in the wrong gear mode, which can cause premature wear or damage over time.
Most vehicles require the transmission to be in Park or Neutral to start. A faulty TRS may intermittently send incorrect signals to the PCM about the actual gear position. When the PCM thinks the transmission is in Drive or Reverse, it will prevent the engine from starting as a safety measure.
Indirectly, yes. A weak battery or charging system issues can cause voltage fluctuations that might trigger various codes, including P0708. However, this is not common. Always check battery voltage and charging system as part of your diagnostic process.
