Code P0846: Transmission Fluid Pressure Sensor Troubleshooting

Your automatic transmission is one of the most complex—and delicately balanced—systems in your vehicle.  When that balance is disrupted because your fluid pressure’s not right, you’re in for a rough ride at the least, and big trouble at the worst. 

It’s the job of your transmission fluid sensor to keep an eye on that pressure.  An OBD-II Code of P0846 is telling you that your sensor isn’t working right.

What is the transmission fluid sensor and what does it do?

Also referred to as Transmission Fluid Pressure Sensor/Switch B Circuit, the transmission fluid sensor is essentially a communication device.  It not only monitors the pressure of your fluid, but it sends important messages to the Transmission Control Module (TCM) about that pressure.

Since hydraulic pressure is the lynchpin that lets your automatic transmission change gears, it needs to be just right; the sensor’s job is to tell your TCM that something’s wrong.

Trouble on the Horizon, how to detect a problem with this sensor?

If you have a sensor issue, it won’t stay a secret for very long.  You’ll pick up on one or more of the following clues:

• Jerky shifting between gears
• Slow acceleration
• Engine revving (increased RPMs) for no apparent reason
• Sticking in neutral
• Overheating
• Decreased fuel efficiency
• “Check Engine” light will come on

Additionally, for some cars, “Limp Mode” may be activated, which is a safety feature designed to limit the vehicle’s operation to avoid accidents.

Any of these signs could be a sign of sensor trouble.  If you experience any of them, you should get off the road as soon as possible and see what the problem is.

What causes a P0846 fault code?

Well, maybe.  Or, more precisely, something you didn’t do.  The most common culprit in transmission malfunction is lack of regular maintenance.  

Low or dirty fluid can cause just about any kind of problem, including throwing your sensor off.  Keeping your system clean can prevent a lot of difficulties.

However, if the fluid isn’t the problem, the next probable cause is electrical. Worn-out wiring can cause incorrect signals to pass from the sensor to the TCM, which in turn can “confuse” your transmission into changing gears irregularly.   

Then there’s also the matter of the pressure switch, which regulates  communication to the working parts of the transmission; if it’s not working properly, your TCM will react to a false message that fluid pressure is wrong, which will throw your gears into erratic behavior.

A third, and less likely possibility, is that one or more actual parts are no longer working.  The key suspects would include the solenoid—a magnetic coil through which electric signals pass—or the sensor itself.

Such mechanical failures would result in loss of control in the amount of fluid that flows, a problem more serious than a simple misread from the sensor.  In such a case, replacing the broken part should solve the problem, although it’s probably going to be the priciest scenario.

Driving with a P0846 Code

Is it possible to drive with a sensor problem?  Technically, yes, at least for a little while—but you shouldn’t, for a couple of reasons.

First, the lack of control over the gear changes and the jerkiness of the ride are a recipe for an accident. Even the best of drivers can’t compensate for unexpected jolts or lack of control over speed.  Driving’s not a good idea, by a long shot.

Second, prolonged driving with any kind of damage in your transmission, whether it be a simple electrical short or the breakdown of a major component, can cause irreparable damage, even to the point of completely burning your transmission out, a totally preventable outcome.  

Trouble shooting at the first sign of problem can save you a lot of time, money, and inconvenience.

How expensive is it to fix a P0846 code?

 If you think transmission problems automatically mean big bucks, you’d be right only some of the time.  It depends on the make and model of your vehicle, of course, but generally speaking, electrical problems aren’t too costly to fix; most of the expense is labor, and should run in the neighborhood of $150 to fix. 

A solenoid can run you in excess of $200, and a sensor replacement can be upwards of $300.  None of that’s too bad, considering how much a transmission rebuild or replacement would drain your wallet—but we won’t go down that road.

Make Prevention Easy

Your best bet is to take good care of your auto by following a regular maintenance routine and by using only the best replacement parts and accessories.  Sun Transmission carries the highest quality components for your transmission, including overhaul and rebuild kits, coolers, pans, gaskets—you name it. 

We also carry a full line of products for your power steering system.  Just let us know what you need and we’ll get it on its way to you!