What is the P0708 Fault-Error Code ?
The P0708 Fault-Error Code is a diagnostic trouble code (DTC) in the vehicle's On-Board Diagnostics II (OBD-II) system. Specifically, it indicates a problem with the Transmission Range Sensor (TRS) circuit, specifically a high input voltage commonly referred to as "Transmission Range Sensor Circuit High Input."
When this code appears, it typically means that the engine control module (ECM) or transmission control module (TCM) has detected a voltage signal from the transmission range sensor (TRS) that is higher than the expected range. Also known as the transmission gear position sensor or neutral safety switch, the TRS is responsible for determining the position of the gear selector (e.g. park, reverse, neutral, drive) and relaying this information to the TCM.
What are the symptoms of P0708 Fault-Error Code ?
When the P0708 fault code appears, it can cause several noticeable signs or symptoms:
Check Engine Light On: The most common indication of the P0708 trouble code is the illumination of the check engine light on the vehicle's dashboard. It is triggered by the engine control module (ECM) or transmission control module (TCM) when it detects a fault in the TRS circuit.
Transmission Shifting Issues: A faulty TRS can cause the transmission to shift erratically or incorrectly. You may experience difficulty shifting, delayed or harsh shifting, or the transmission may not shift into certain gears.
Stalling: In some cases, a faulty TRS can cause the engine to stall, especially when shifting or stopping. This is because the ECM or TCM may not receive the correct signal from the TRS, causing the engine and transmission to operate incorrectly.
Failure to Start: If the TRS fails completely or provides inaccurate readings, it can prevent the vehicle from starting, especially if it is unable to detect when the transmission is in "Park" or "Neutral." Continuing to operate with a faulty TRS can result in increased difficulty starting the vehicle and potentially leave you stranded.
Limited or No Reverse: A faulty TRS may prevent the vehicle from shifting into reverse or cause problems when trying to shift into reverse.
Other Transmission-Related Problems: In addition to shifting problems, other transmission-related problems can also occur, such as shifting problems, transmission overheating, or unusual noises coming from the transmission.
Loss of Driveability: In general, a faulty TRS can affect the driveability and performance of a vehicle. The vehicle may slow down, lose power, or exhibit abnormal behavior while driving.
What could be the causes of the P0708 Fault-Error Code ?
There are several possible causes that can trigger the P0708 fault/error code, including:
Faulty Transmission Range Sensor (TRS): A faulty TRS is one of the most common causes of code P0708. The TRS may have internal electronic issues, wear, damage, or misalignment, causing it to produce a higher voltage signal than expected.
Wiring Issues: Damage, corrosion, or poor connections in the wiring harness associated with the TRS circuit can cause the voltage signal to be higher than expected. This can include broken wires, corroded connectors, or shorts to power.
Improper Transmission Range Sensor Alignment: Misalignment of the TRS can cause it to produce incorrect voltage signals, leading to code P0708. Misalignment can be caused by wear or improper installation.
Faulty ECM or TCM: In rare cases, a fault in the engine control module (ECM) or transmission control module (TCM) could be responsible for code P0708. However, this is less common than issues with the transmission range sensor or wiring.
Other Electrical Issues: Other electrical issues such as a short or open circuit in the vehicle's wiring system could potentially cause the voltage signal to be higher than expected.
What Steps Should Be Followed to Resolve P0708 Fault-Error Code ?
Steps to follow to resolve a P0708 Fault-Error Code:
Read Code: Use an OBD-II scanner to retrieve trouble code P0708 and any other related codes stored in the vehicle's ECM or TCM. Write down any codes present as they may provide additional information about the problem.
Check Transmit Range Sensor (TRS): Inspect the transmit range sensor (TRS) to ensure it is properly aligned and functioning properly. Verify that the TRS is providing accurate voltage readings within the specified range.
Inspect Wiring and Connectors: Thoroughly inspect the wiring harness associated with the TRS circuit. Look for any signs of damage, corrosion, or poor connections. Repair or replace damaged wiring as necessary. Make sure connectors are properly seated and free of corrosion.
Test TRS Signal: Use a multimeter to test the voltage signal output of the TRS while the gear selector is moved through its range of positions. Compare the measured voltage readings with the specifications stated in the vehicle's service manual.
Check ECM/TCM Communication: Use diagnostic tools to scan the ECM and TCM for any internal faults or communication issues with the TRS circuit. Ensure the modules are receiving and transmitting signals properly.
Clear Codes and Test Drive: After completing repairs, clear any trouble codes stored in the ECM or TCM using an OBD-II scanner. Take the vehicle for a test drive to ensure the P0708 code does not return and the transmission is functioning properly.
Recurrence Monitor: Pay attention to vehicle performance and check for a recurrence of code P0708. If the code returns, recheck all components and wiring to identify any issues you may have missed.
What Are the Long-Term Effects of the P0708 Fault-Error Code ?
Some potential long-term effects of the P0708 Fault-Error Code include:
Transmission Damage: A faulty Transmission Range Sensor (TRS) can lead to transmission-related issues such as difficulty shifting, harsh shifting, or transmission slipping. Over time, these issues can cause increased wear and tear on transmission components, potentially leading to premature transmission failure.
Reduced Fuel Efficiency: Issues with the TRS or its circuitry can affect the efficiency of the transmission and overall drivetrain. This can lead to reduced fuel efficiency over time as the engine may operate less efficiently due to improper gear selection or transmission control.
Difficulty Starting Vehicle: If the TRS fails completely or provides inaccurate readings, it can prevent the vehicle from starting, especially if it is unable to detect when the transmission is in "Park" or "Neutral." Continuing to operate with a faulty TRS can result in increased difficulty starting the vehicle and potentially leave you stranded.
Transmission Overheating: A faulty TRS can cause the transmission to not function properly, causing increased friction and heat generation. Over time, this can cause the transmission to overheat, which can further damage transmission components and lead to transmission failure.
Safety Concerns: Faulty transmission components, such as the TRS, can compromise a vehicle’s drivability and safety. Erratic shifting, delayed engagement, or other transmission-related issues can affect a vehicle’s handling and response, potentially leading to unsafe driving conditions.
In general, it is very important to address a P0708 trouble code immediately to prevent any potential long-term effects on the vehicle's transmission, driveability, fuel efficiency, and safety. Ignoring the problem or delaying repairs could lead to more significant problems and higher repair costs in the future.
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