P0705 is a very common transmission-related trouble code that can occur in the GMC Sierra. In layman’s terms, it means that your Sierra can’t tell what gear you’ve selected, which can have some real consequences on how it drives.
It’s most likely caused by a bad Transmission Range Sensor (TRS), but there are other causes that we’ll cover in the diagnosis section below.
P0705 Definition: TRS – Circuit Malfunction
Here’s the meaning of P0705, divided into its two main parts:
TRS
The Transmission Range Sensor (TRS) is responsible for telling your Sierra’s Powertrain Control Module (PCM) or Transmission Control Module (TCM) what gear the vehicle is in. For this article, we will use PCM as the preferred term.
Perhaps the most common fix for P0705 is a new TRS. Usually, you’ll find the TRS bolted to the transmission, which makes it easy to find and replace. Unfortunately, on some transmissions, it can be located on the inside, which makes replacing it at home nearly impossible.
Circuit Malfunction
A circuit malfunction means the TRS is not sending the proper signal to the PCM. There might be no signal at all, or the voltage value is not within the range of any gear. Either way, P0705 will be stored in the PCM’s memory, and the check engine light will come on.
GMC Sierra: P0705 Symptoms
The symptoms associated with P0705 in the GMC Sierra are going to vary depending on how the PCM reacts to not receiving a signal from the TRS (which can change depending on the model year and the equipped transmission).
Here are the most common symptoms:
- No start (the neutral safety switch doesn’t know what gear the transmission is in). See if it’ll start in neutral.
- Strange shift patterns (usually early shifts)
- Decreased MPG
- Delay between selecting a gear and transmission engagement
- No reverse lights
GMC Sierra: P0705 Causes + Diagnosis
If your Sierra has an internal TRS, there’s not much you can do to troubleshoot it at home. On the other hand, if it’s external, here are some general steps you can follow.
You’ll need to find the shift linkage on the transmission.
Inspect the TRS
Inspect the TRS to see if there are any glaring problems. First, take a look at where the wiring harness plugs into it. Make sure that it’s still plugged in tight. Make sure there are no bent or pushed-out pins in the sensor.
If it’s plugged in tight and the pins look good, it’s time to move on to the wiring harness. Make sure that it is not burnt, cracked, shorted, or damaged. This is a common issue if your GMC Sierra has P0705.
If it starts in gear but not in neutral, the TRS could be out of alignment. There should be a neutral alignment mark on it.
TRS Replacement
Outside of a wiring or alignment issue, there’s not much else that can cause P0705 other than replacing the TRS.
Assuming the TRS is on the outside of the transmission on your Sierra, replacing it is usually pretty straightforward. Some are more forgiving than others when it comes to aligning them; follow the directions and alignment marks, and you should be fine.
Conclusion
A bad TRS usually causes P0705. Where that TRS is located (in or on the transmission) is going to dictate whether or not you can do anything about it at home. Good luck fixing your Sierra!