GMC Terrain P0841: Meaning, Causes, + Diagnosis

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P0841 GMC Terrain

P0841 is a relatively common trouble code.  While your GMC Terrain’s check engine light will come on, this particular code indicates that there’s something wrong with the transmission, specifically the transmission fluid pressure sensor circuit.

It’s a generic code, so P0841 has the same definition for any vehicle made for the 1996 model year and up.  Before doing anything, check your Terrain’s transmission fluid.

Abbreviations used in this article:

  • PCM– Powertrain Control Module, this is the main computer module with the engine and transmission control in one unit. 
  • TCM– Transmission Control Module, the TCM controls the shifting of the transmission and is separate from the engine control module. Your GMC Terrain will either have a PCM or a TCM.  And, for the purposes of this article, they are interchangeable.
  • TFPS– Transmission Fluid Pressure Sensor

P0841 Definition:  Transmission Fluid Pressure Sensor/Switch “A” Range/Performance

P0841 Definition: GMC Terrain

Here’s the definition of P0841 for the GMC Terrain broken down by its individual parts. 

Transmission Fluid Pressure Sensor/Switch

The TFPS has two primary jobs:

  1. Convert the transmission fluid pressure into a signal that the PCM (or TCM) can use to control shifts.
  2. Verifies that the PCM/TCM’s request for a transmission shift has occurred.

Circuit “A” Range/Performance

The TFPS converts the hydraulic pressure data into a voltage signal that your Terrain’s TCM/PCM can use to control the transmission.  P0841 occurs when this signal is out of the normal operating range for this signal.

P0841 Symptoms:  GMC Terrain

Here are the most common symptoms associated with P0841:

  • Limp Mode– Your Terrain will shift differently and won’t have access to all of its gears.
  • Check Engine Light– There will often be other codes that occur with P0841.  They will usually be related to voltage and power.
  • Erratic Shifting– Shifts may feel soft (RPM slowly drops during the shift), or they may feel too harsh (abrupt drop in RPM).

GMC Terrain P0841 Causes + Diagnosis

P0841 Diagnosis Terrain

Diagnosing P0841 in the GMC Terrain can be challenging, due to the location of the TFPS sensor and the wiring associated with it.

1. Check for Other Codes and TSB’s

The first thing you want to do is check for other diagnostic codes.  They can provide valuable clues to what’s going on inside your transmission.

TSB’s are technical service bulletins.  GMC uses them out to deal with common and well-known vehicular issues.  Check to see if there are any related to your problem.  You can get them from the NHTSA website.

2. Inspect the TFPS Wiring

The next thing you’re going to want to do is inspect the wiring going to your Terrain’s TFPS.  If it’s burnt or damaged, you’ll need to replace/repair it.

After that, clear your Terrain’s trouble codes and see if P0841comes back.9

Whether or not you’re going to be able to access the TFPS is going to determine whether most people can continue diagnosing P0841.  Sometimes the TFPS can be accessed from the outside of the transmission.  You may need to open the transmission.

Wiring issues are the most common cause of P0841.  Take your time and make sure that the harness is in good shape.

3. Other Causes

While a bad TFPS sensor is highly likely, make sure that the voltage going to it is correct and doesn’t change when wiggling the harness before replacing it.

Conclusion

Diagnosing P0841 is pretty straightforward.  The real issue is getting to the wiring and TFPS.  Good luck fixing your Terrain!