Fault code P0708 – transmission range sensor “A” circuit high input

Fault code P0708 is called “Transmission Range (TR) Sensor “A” Circuit High Input” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P0708

Diagnostic Trouble Code P0708 (DTC) refers to the transmission switch. Its function is to tell the transmission control module (PCM) the gear shift position.

Fault code P0708 – transmission range sensor

The code reports that the computer has detected a TR sensor malfunction. The sensor sends a high level signal to the computer determining the gear position. The control module receives signals from the vehicle speed sensor as well as the TR.

When the vehicle is moving and the computer receives conflicting signals due to the high signal level, for example, the TR signal indicates that the vehicle is parked. However, the speed sensor indicates that it is moving, code P0708 is set.

TR sensor failure is common with age and high mileage. It is susceptible to weathering. Like any printed circuit board, it is subject to corrosion over time. On the plus side, they don’t require expensive repairs and are easy to replace with a little automotive repair experience.

Modern models with a transmission range sensor located in the valve body are a different design. The range sensor is separate from the neutral safety switch and reverse shifter.

The function remains the same, but the replacement has become a more serious matter, both in complexity and cost. The easiest way to determine what type is used in your car is to find the part on your local auto parts website.

Symptoms of vehicle malfunctions

The main signal that an error P0708 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. The “Check engine” control lamp on the control panel will light up (the code will be stored as a fault).
  2. The reverse lights may not work.
  3. In some cases, the engine will only start in neutral.
  4. There may be problems with gear engagement and disengagement.
  5. Floating revolutions when shifting gears.
  6. Transmission may display delayed engagement.
  7. Increased fuel consumption.

The severity of error P0708 varies from medium to severe. The engine may stop starting. It is also possible for the transmission to enter the emergency operation mode.

Factors that can cause this error code

The error code P0708 can mean that one or more of the following problems have occurred:

  • Transmission range sensor is defective.
  • TR sensor is loose or incorrectly adjusted.
  • Short circuit, open circuit, or damaged ACC selector position sensor connector.
  • ATF transmission fluid is contaminated or low.
  • Clogged or clogged transmission fluid passages.
  • Damage to the transmission valve body.
  • Sometimes the cause is a faulty PCM module.

How to fix or reset OBD-2 code P0708

Some suggested steps for troubleshooting and fix the error code P0708:

  1. Change ATF fluid and filter.
  2. Fill transmission fluid to required level.
  3. Flushing to clean inside channels of transmission.
  4. Testing, if necessary replacing faulty transmission range sensor.
  5. Troubleshooting mechanical problems inside the transmission.
  6. Checking connectors as well as wiring.
  7. Flashing or replacing the PCM.

Diagnose and repair of problems

Always check the maintenance bulletins (TSB) for your particular vehicle to get started. The P0708 problem may already be a known problem with a known fix issued by the manufacturer. This can save you time and money during diagnosis.

The next step is to locate the transmission range sensor (TRS). Once found, visually inspect the connector and wiring. Look for scratches, scuffs, exposed wires, burn spots or melted plastic.

Disconnect the connector and carefully inspect the terminals inside the connector. Look to see if they look burnt or have a green tint indicating corrosion. If you need to clean the terminals, use an electrical contact cleaner and a plastic-bristle brush. Allow to dry and apply electrical grease to the contact areas of the terminals.

Using a diagnostic tool, clear the trouble codes from the memory and see if error P0708 returns. If the code returns, we will need to test the TR sensor and associated circuits.

Wiring test

With the ignition key off, disconnect the electrical connector on the TR sensor. Connect a digital voltmeter. The black wire to ground and the red wire to the signal terminal on the transmission range sensor wiring harness connector.

Turn on the ignition key. Depending on the manufacturer’s specifications, the voltmeter should show either 12 volts or 5 volts. Jerk the connection and see if the reading changes. If the voltage is incorrect, replace the faulty wires or connector.

Check sensor

Connect one ohmmeter lead to the signal terminal on the transmission range sensor and the other to ground. Check the resistance against the manufacturer’s specifications. Jiggle the connector on the TRS sensor, checking the resistance. If the ohmmeter reading differs from the manufacturer’s recommendation, replace the sensor.

If the wiring and sensor tests are done, but you keep getting code P0708. You need to look at the PCM / TCM module as well as internal transmission failures. But you need to do this after replacing the TRS sensor. More often than not, it is the one that is the problem.

If you are unsure, ask a qualified automotive diagnostician for help.

On which vehicles does this problem occur most frequently

Fault code P0708 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Chevrolet (Silverado)
  • Dodge
  • Ford (Explorer, F-150, Mondeo, Ranger, Windstar)
  • Honda
  • Hyundai (Accent, Elantra, Santa Fe, Solaris, Sonata, Tucson)
  • Kia (Rio)
  • Mazda (626, Tribute)
  • Mitsubishi
  • Saturn (SL2)
  • Ssangyong (Kyron)
  • Subaru

Fault code P0708 can sometimes be found with other errors. The most common are the following: P0113, P0118, P0123, P0453, P0700, P0705, P0706, P0709, P0717, P0722, P0743, P0795.

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