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Error code P0705 is defined as Transmission Range Sensor Circuit (TRS) Malfunction (PRNDL Input), relating trouble to Transmission Control Module (TCM) as it receives an error input from the TRS usually caused open or short in the TRS, defective TRS, TCM, or PCM.
This error code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II system, especially those made since 1996 up to present. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.
Error code P0705 indicates the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) or the TCM has received an input error coming from the TRS. This switch is also called by other names like pressure switch, PNP or Park Neutral Position switch, gear selection switch, or PRNDL input switch. The TRS or PRNDL input switch works by sending the position of the shift lever to the PCM or the TCM. It’s commonly located just outside the transmission, while some makes and models are housed it inside the valve body.
Error code P0705 is set when the PCM doesn’t receive an input, or if it receives logically impossible input, such as when the vehicle is going 50 mph, but the TRS tells the PCM that it’s in Reverse. In some cases, faulty TRS will tell the PCM that the vehicle is in more than one gear simultaneously.
There are actually 3 types of TRS:
- Contact Type – composed of a simple set of switches that communicates to the PCM and sends the information regarding the exact shifter level position. This type of TRS uses different wire for each position of the shifter.
- Pressure Range Switch – this is bolted to the valve body of the transmission and works by opening and closing different passages for the transmission, fluid as the shift lever moves. Each time the gear position moves, transmission fluid will be activated through a different passage, which will be read by this sensor.
- Variable Resistor – this type contains a series of resistors tied to the same voltage output. The resistor works by absorbing a certain amount of voltage; each gear has its personal resistor in its circuitry and will be used depending on the PRNDL.
As with other codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. In many cases, the vehicle will also experience no start condition. For the motorists’ safety, the TRS will only allow the vehicle to start at Park or Neutral position. This is a safety feature to keep the vehicle from starting unless the owner is actually already behind the wheel and ready to get full control of the vehicle. Other common symptoms also include:
- Unable to go in or out of gear or shift properly
Multiple factors lead to this code, such as:
- Defective TRS
- Open or short in the TRS circuit
- Faulty PCM or TCM
- Misadjusted shift linkage
- Dirty and contaminated transmission fluid
- Defective transmission valve body
How to Check
Technicians start their diagnosis by making sure there is proper voltage and ground present in the TRS.
Then, they test a Contact form of TRS by back probing each wire on the sensor while another person changes the gears to verify for each correct output. There should be a change in voltage each time the gear is changed in position. The mechanic usually knows the specific voltages.
Then, they test the Variable Resistor form of a TRS using a multimeter to measure the amount of voltage the reference wire outputs. The reference wire will send different voltages to the PCM each time the gear changes. If the reference voltage doesn’t change or is nonexistent, then the sensor is bad, or the wire is at fault.
If this is the case, then the mechanic will test the TRS to verify which wires are output to ground. Most sensors of this type use a ground connector as its form of output. As the driver changes gear, the valve body will allow transmission fluid through different passages. The transmission fluid goes through the different passages, the TRS will output a different ground. To see which ground wire coincides with which gear, an accurate wiring diagram of the sensor must be located. Certified mechanics usually have a wiring diagram.
How to Fix
The easiest fix for this code is to repair open or short in the TRS circuit. Other repair methods include:
- Replacement of defective TCM
- Replacement of defective PCM
- Replacement of the transmission fluid and filter
- Adjusting the linkage connecting the shift lever on the transmission to the gear shifter inside the vehicle
When diagnosing this code, it is important to check the transmission fluid as well. Many times, dirty or contaminated transmission fluid is the cause of the problem, which can be easily fixed.