Skip the auto shop - Our mechanics make house calls

P0849 OBD-II Trouble Code: Transmission Fluid Pressure Sensor/Switch B Circuit Intermittent

diagnostic check engine light

P0849 code definition

The P0849 code identifies a problem with fluid levels within the transmission. The powertrain control module controls a number of internal components within an automatic transmission, and the same control module is capable of detecting this fault. If the pressure at the pump within the transmission is not at the level required by factory specifications, then it will store a code via the powertrain control module.

What the P0849 code means

P0849 is the OBD-II generic code for a fault involving the pressure of fluid within an automatic transmission. The fluid inside of the transmission is responsible for tasks such as shifting into and out of gear, along with controlling the lockup of the torque converter. Pressure is maintained by a pump that regulates the fluid pressure. All of these components are controlled by the powertrain control module. Throttle position, engine speed, vehicle speed, and engine load are used to calculate the proper gear for the transmission to operate in. Without proper fluid pressure, the transmission may not be able to do that job effectively.

What causes the P0849 code?

The P0849 code has a number of common causes:

  • Blockage within hydraulic lines inside of transmission
  • Faulty solenoid within transmission
  • Faulty sensors within the transmission
  • Fault or electrical short in the powertrain control module
  • Low transmission fluid
  • Dirty or contaminated transmission fluid
  • Mechanical failure of transmission internal parts

What are the symptoms of the P0849 code?

Since the P0849 code deals with a problem with fluid levels in the transmission, there are a number of symptoms that accompany its appearance that are noticeable to the driver. If the vehicle has a warning light on the dashboard that is specifically intended to warn the driver of transmission issues, then this light should illuminate as soon as the required pump pressure within the transmission is not detected. After a few more instances of this fault, the Check Engine light should illuminate.

Physical symptoms such as rough shifting and slipping within the transmission will also accompany this fault. In severe cases, the transmission temperature may increase dangerously and fuel economy may suffer.

How does a mechanic diagnose the P0849 code?

The P0849 code will be diagnosed by a certified technician using an OBD-II scanner that is capable of retrieving the factory readings from the vehicle. The mechanic will view the fault code and see when it originally occurred. Then, the code will be reset and the vehicle will be taken for a test drive. If the code appears once again during this test drive, then the technician can confirm that the problem is not intermittent.

To test the electrical components around the circuits controlling the automatic transmission, the technician will then use a voltmeter to test various points around the circuit to confirm that proper amounts of power are flowing through the circuits. After all of that has been completed, the technician will check the transmission fluid itself. Low, contaminated, or old transmission fluid can cause the P0849 code to appear.

Common mistakes when diagnosing the P0849 code

Often the P0849 code is interpreted as a serious problem within the automatic transmission. While this may be true, it is just as likely that the problem is either electrical or due entirely to old, low, or dirty fluid in the transmission.

How serious is the P0849 code?

The P0849 code can range from moderately serious to very serious, depending on the root of the problem. If this code appears, it should certainly be diagnosed by a qualified technician promptly. In serious cases, there are parts within the transmission that need to be replaced before the vehicle can run properly once again. In moderate cases, the technician will simply have to add more fluid to the transmission. Having this problem addressed as soon as it appears it the best way to avoid costly major repairs down the road.

What repairs can fix the P0849 code?

The most common repairs to address the P0849 code are as follows:

  • Repair or replace wiring harness around transmission
  • Repair or replace powertrain control module
  • Repair or replace connections among wiring surrounding transmission or powertrain control module
  • Replace transmission fluid
  • Rebuild or replace automatic transmission

Additional comments for consideration regarding the P0849 code

The P0849 code can appear for a number of reasons relating to electrical issues or issues with the transmission fluid itself. Have the problem thoroughly diagnosed by a qualified technician prior to replacing any components in or around the transmission.

Need help with a P0849 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.


Post a question and get free advice from our certified mechanics.


More related articles

P0121 OBD-II Trouble Code: TPS "A" Circuit Range Performance Problem
P0121 code definition Throttle Pedal Position Sensor/Switch (TPS) A Circuit Range Performance Problem What the P0121 code means P0121 is a generic OBD-II code which indicates that the Engine Control...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the P0052 code means This code is seen when the Engine Control Module (ECM) tries to control the...
How to Get a Louisiana Driver's Permit
s licensing program. The first step in this program is to obtain...

Related questions

Q: engine codes related

Hey there. If the codes are cleared with a scanner, check to see if they return. Maybe the system was serviced or the battery ground is loose and causing the circuit to break which could cause a lack of communication...

Q: AT light and Check engine light on stuck in third gear.

A logical place to start is with a Check Engine Light inspection to see what codes might be set. Usually with something of this nature, codes will be present, and there will be a flow chart that should be used...

Q: P0016 (crankshaft and camshaft correlation bank 1 sensor A)

Hello. Trouble code P0016 is set when the computer detects that there is an issue with the timing between the engine's camshaft and crankshaft signals. The camshaft and crankshafts are connected by a belt or chain, and are precisely timed...