This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.
P0705 - Transmission Range Sensor Circuit Malfunction (PRNDL Input)
Transmission trouble is never good news, but it isn’t always cause to grab your wallet and hold on either. A P0705 code indicates that your vehicle Engine Control Module (ECM) or Transmission Control Module (TCM) got an input error from the Transmission Range Sensor (TRS).
The TRS goes by many names, too: the pressure switch, Park Neutral Position switch (PNP), the gear selection switch, or a PRNDL input switch. This “alphabet soup” of acronyms all boils down to a singular purpose: the TRS tells the TCM or ECM the current position of the shift lever, so the computers that control the transmission can put it into the correct gear.
Most vehicles have their TRS located on the outside of the transmission, but there are models that place it inside the transmission on the valve body. In other words, some are more vulnerable to faults than others, and some are a cast-iron pain to verify a fault compared to others.
If you hook up your scanner and pull a P0705, it means the ECM or TCM got an impossible input signal from the TRS. How is such a signal “impossible”? Let’s say you’re driving 60 MPH in commuter traffic, but the TRS sends a signal to the TCM/ECM that the shifter is currently in the Reverse position. Not a likely or realistic scenario. There are even a few recorded instances where an ECM got telemetry from the TRS that the vehicle was in two gears at the same time. At any rate, once the signal is received, the TCM/ECM saves the P0705 code.
As with most sensor related diagnostic codes, there is a very short list of what could be causing the P0705. Here’s what should be checked first.
- Damaged, worn or corroded TRS wiring or connectors.
- Damaged/faulty TRS
- Damaged/faulty TCM or ECM
- Misadjusted shift linkage
- Dirty/contaminated transmission fluid
- Damaged/faulty transmission valve body
Certain vehicles will actually lock into a non-start state following a P0705, especially if the TRS is sending out a signal other than Park or Neutral. For decades, vehicles will not start unless the shift lever is in Park or Neutral as a safety feature to prevent motorists from losing control of their vehicle on startup. Other symptoms of a P0705 include a transmission that won’t lock into each gear as you accelerate or decelerate. You may also observe the vehicle may not shift properly or smoothly between gears. Naturally, your Check Engine Light should be illuminated on the dashboard, too.
Handling this trouble code on your own is not recommended beyond basic diagnostic checks like examining the wiring or sensor for physical damage. You will need a multimeter, and advanced program-capable OBDII scan tool, and the ability to access the transmission and transmission valve body. Here’s an overview of the troubleshooting process to give you an idea of what you’re up against:
- The first step is a two person job: One technician checks for proper voltage and ground presence at the TRS another tech changes the gears. Tech one is verifying correct voltage output for each gear change while watching for specific voltages that are within the manufacturer’s specified ranges.
- Next, a similar two person test is performed using the ends of the wiring harness instead of verifying the voltage output from the sensor itself.
- Similar tests are performed on variable resistor and pressure range switch TRS systems, but the results will give you one of a few answers: the wiring is at fault, the sensor is at fault, or the vehicle has serious issues with the ECM/TCM.
- If you think you can handle the diagnostic yourself, definitely consult a site like ProDemand for TRS specs and voltage ranges for your vehicle before you start testing.
Any time you see a transmission-related trouble code, the first thing you should do is check your transmission fluid. Contaminated or dirty transmission fluid can create all kinds of phantom problems with your transmission that store any number of OBDII codes. Start with a fluid check before you end up doing any unnecessary repairs.
How serious is this?
In the short term, this code won’t do anything catastrophic, but it won’t pass inspection. About the worst you can anticipate is a potential no-start condition and a Check Engine Light. You may also experience erratic shifting until you correct the underlying problem, and some vehicles will engage “limp mode” and prevent your vehicle from exceeding 40 MPH.
What repairs can fix the code?
Here’s what an expert will typically recommend to fix a P0705 code:
- Repairing/replacing an open or short circuit in the TRS wiring (can be labor intensive, fairly inexpensive)
- Replacing a faulty TCM (not common, labor intensive, somewhat expensive)
- Replacing a faulty ECM (not common, labor intensive, moderately expensive)
- Changing the transmission fluid and filter (needs to be done at regular intervals throughout the life of your vehicle.
- Adjusting the linkage connecting the shift lever on the transmission to the gear shifter inside the car (time-consuming, labor intensive, not expensive)
If your vehicle isn’t locked in a non-start state and is drivable, take it to a service center or repair shop as soon as possible. Pull the code for yourself if you want, but a P0700 series code means you will want a professional to do the work for you on this one. It’s complex, labor intensive and better left to experts.
A PDF VERSION OF THIS ARTICLE FOR LATER