What Does OBD2 Code P0705 Mean?
The OBD2 code P0705 signals a “Transmission Range Sensor Circuit Malfunction (PRNDL Input)”. This diagnostic trouble code is generic, applicable across various vehicle makes and models from 1996 onwards. However, specific diagnostic and repair procedures can differ based on your vehicle’s design.
At its core, the P0705 code indicates an issue with the Transmission Range Sensor (TRS), sometimes also referred to as the Park/Neutral Position (PNP) switch or Manual Lever Position Sensor (MLPS). This sensor, located either externally or internally within the transmission, plays a crucial role in informing your vehicle’s computer – the Powertrain Control Module (PCM) or Transmission Control Module (TCM) – about the gear shift lever’s position. This includes Park (P), Reverse (R), Neutral (N), and Drive (D). In some vehicles, the TRS also activates the reverse backup lights.
When your vehicle’s computer detects an irregular or absent signal from the TRS regarding the gear position, the P0705 code is triggered. The computer relies on signals from both the TRS and the vehicle speed sensor to understand the vehicle’s operating state. A conflict arises when these signals contradict each other. For instance, if the TRS signal suggests the vehicle is in Park, but the speed sensor indicates movement, the computer recognizes a malfunction and sets the P0705 code.
External TRS units are prone to failure due to their exposure to harsh environmental conditions over time. Corrosion and wear on the printed circuits within these sensors are common issues with age and mileage. Fortunately, replacing an external TRS is typically straightforward and relatively inexpensive, even for those with limited automotive repair experience.
Example of an External Transmission Range Sensor (TRS):
Image of an external type Transmission Range Sensor, commonly found on older vehicles.
In contrast, newer vehicle models often house the TRS internally within the transmission valve body. While the function remains the same – to accurately report gear position – internal TRS replacement is significantly more complex and costly. Internal TRS units are distinct from the neutral safety switch and reverse backup light switch, focusing solely on gear position sensing. To determine whether your vehicle uses an external or internal TRS, a simple check on an auto parts website can be helpful. If the part is readily listed, it’s likely external. Absence from parts listings often indicates an internal TRS.
Common Symptoms of a P0705 Code
When the P0705 code is active, you might observe several symptoms affecting your vehicle’s operation:
- Malfunction Indicator Lamp (MIL) Activation: The check engine light on your dashboard will illuminate, indicating a detected issue, accompanied by the P0705 DTC stored in the vehicle’s computer.
- Backup Lights Malfunction: Your reverse lights might fail to turn on when the vehicle is shifted into reverse, as the TRS often controls this function in external setups.
- Starting Issues: You may need to wiggle the gear shift lever to find the correct “sweet spot” for the starter to engage. This indicates poor contact within the TRS. In some cases, the engine might not start at all.
- Neutral Start Only: The engine might only start when the gear selector is in the Neutral position, regardless of other gear selections. Conversely, it could start in any gear due to incorrect gear position signaling.
- Erratic Shifting: The transmission might exhibit irregular shift points (RPMs) due to the computer receiving incorrect gear position data.
- Reduced Fuel Economy: Inefficient gear shifts and transmission operation due to faulty gear position readings can lead to a decrease in fuel efficiency.
- Delayed Transmission Engagement: When shifting into Drive or Reverse, there might be a noticeable delay before the transmission engages, impacting smooth vehicle operation.
- Toyota Specific Symptoms: Toyota vehicles, including trucks, may display unusual instrument cluster readings, such as flickering lights or inaccurate gauge readings, in conjunction with a P0705 code.
Potential Causes of a P0705 Code
Several factors can lead to a P0705 trouble code. Identifying the root cause is crucial for effective repair:
- Misadjusted or Loose TRS: If the Transmission Range Sensor is not correctly aligned or has become loose, it can send inaccurate signals.
- Defective TRS Unit: The sensor itself might be faulty due to wear, internal circuit damage, or age-related degradation.
- Connector Issues: Problems with the electrical connector at the external TRS, such as corrosion, bent pins, loose connections, or pushed-out pins, can disrupt signal transmission.
- Wiring Harness Damage: The wiring harness connected to an external TRS can be damaged, shorted, or broken due to rubbing against the transmission linkage or other components, compromising the electrical circuit.
- Internal Valve Body Issues (Internal TRS): For vehicles with internal TRS units, blockages within the valve body’s TRS port or a defective internal sensor can cause the P0705 code.
Diagnosing and Repairing OBD2 Code P0705
Diagnosing and repairing a P0705 code varies significantly depending on whether your vehicle uses an external or internal Transmission Range Sensor.
Internal TRS Diagnosis and Repair:
Internal TRS replacement is generally more complex and often requires specialized tools and expertise. Typically, diagnosis involves using a diagnostic scan tool like a Tech II to confirm the sensor malfunction. Repair usually necessitates draining the transmission fluid and removing the transmission pan to access the valve body. The TRS is located within the valve body, submerged in transmission fluid. Issues often arise from restricted hydraulic flow or failing O-ring seals within this environment.
Due to the complexity, internal TRS issues are best addressed by a qualified transmission specialist. Attempting DIY repair without proper knowledge and tools can lead to further complications and damage.
External TRS Diagnosis and Replacement:
Replacing an external TRS is a more DIY-friendly task. Here’s a step-by-step guide:
- Safety First: Ensure the vehicle is parked on a level surface, wheels are blocked to prevent rolling, and the parking brake is firmly engaged.
- Shift to Neutral: Place the transmission gear selector in the Neutral (N) position. This is crucial for proper sensor alignment.
- Locate the TRS: Identify the transmission shift linkage. On front-wheel-drive vehicles, it’s usually on top of the transaxle. On rear-wheel-drive vehicles, it’s typically on the driver’s side of the transmission.
- Inspect the Electrical Connector: Carefully disconnect the electrical connector from the TRS. Thoroughly examine both the sensor and harness side of the connector for corrosion, bent pins, or damage. Clean corroded connectors with electrical contact cleaner. Apply dielectric grease to the connector terminals before reconnecting to prevent future corrosion.
- Check Wiring Harness: Inspect the wiring harness leading to the TRS for any signs of damage, such as chafing, cuts, or melted insulation, especially where it might rub against the shift linkage. Repair any damaged wiring.
- Sensor Looseness and Adjustment (Initial Check): Check if the TRS is loose on the transmission. If loose, with the parking brake on and transmission in Neutral, turn the ignition key to the “ON” position (engine off). Gently rotate the TRS until the backup lights illuminate. Once the backup lights are on, carefully tighten the TRS mounting bolts. For Toyota vehicles, the adjustment procedure might involve aligning the sensor using a 5mm drill bit inserted into a specific alignment hole before tightening. Consult your vehicle’s repair manual for precise procedures.
- Sensor Removal:
- Remove the nut securing the gear shift lever to the TRS shaft and detach the lever.
- Disconnect the electrical connector from the TRS again.
- Remove the two bolts that secure the TRS to the transmission. Be careful not to drop these bolts as they can be difficult to retrieve.
- Carefully lift the old TRS unit off the transmission.
- New Sensor Installation:
- Compare the new TRS with the old one, ensuring it’s the correct part and visually checking for any differences.
- Note the alignment marks on the new sensor shaft and housing, typically indicating the Neutral position. Ensure these marks are aligned as per the manufacturer’s instructions before installation.
- Install the new sensor onto the shift lever shaft, aligning it correctly.
- Install and tighten the two mounting bolts to the specified torque.
- Reconnect the electrical connector to the TRS.
- Reinstall the gear shift lever and tighten the retaining nut.
Additional Notes: On some Ford vehicles, an external TRS might be termed a Manual Lever Position Sensor (MLPS). Always refer to your vehicle-specific repair manual for accurate terminology and procedures.
Related OBD2 Codes: Codes related to the Transmission Range Sensor circuit include P0706, P0707, P0708, and P0709, each indicating a slightly different aspect of the TRS circuit malfunction.
Need More Help with P0705?
For further assistance with diagnosing and resolving the P0705 trouble code, consider consulting a certified mechanic or utilizing online car repair forums for community-based troubleshooting advice.
Disclaimer: This information is intended for informational purposes only and should not be considered professional repair advice. We are not liable for any outcomes resulting from actions taken based on this information. Always prioritize safety and consult qualified professionals when performing vehicle repairs. All content is copyright protected.
