Failed transmission fluid pressure sensor/switch (both sources; OBD-Codes.com rates it the likely cause). Intermittent open, short to voltage or short to ground in the sensor signal circuit (OBD-Codes.com; RepairPal lists a wiring issue). Corroded external connector terminals (OBD-Codes.com says this is the most common area of concern). Internal mechanical transmission problem such as internal leaks, damaged check balls, low line pressure or a stuck valve (OBD-Codes.com rates it possible). Low transmission fluid level (RepairPal). Faulty PCM or TCM (both sources; OBD-Codes.com rates it unlikely and says a replacement must be programmed). The sources differ: RepairPal adds low fluid level, while OBD-Codes.com focuses on the electrical circuit plus internal mechanical faults.

Clean or repair corroded connectors and damaged or loose wiring. Top up the transmission fluid to the correct level. Replace the transmission fluid pressure sensor/switch. Repair internal transmission faults if the sensor and wiring check out. Replace and program the PCM/TCM only after other causes are ruled out.

P0849🔧 Transmission / Fluid pressure sensorsStop and fix promptly

P0849: Transmission Fluid Pressure Sensor/Switch B Circuit Intermittent (Meaning, Causes, Fixes)

Q: What does P0849 mean?

P0849 means the transmission computer is seeing an on-and-off (intermittent) problem in the signal from transmission fluid pressure sensor/switch "B". OBD-Codes.com says it is usually an electrical circuit problem, like a loose or corroded connection or a failing sensor, but that internal mechanical problems in the transmission can also set it. RepairPal also lists low transmission fluid and a failed TCM. An automatic transmission uses fluid pressure to apply its clutches and change gears. A transmission fluid pressure sensor/switch (TFPS) turns that pressure into an electrical signal so the powertrain control module (PCM), or a separate transmission control module (TCM), can tell the operating pressure or when a shift is happening. OBD-Codes.com says the TFPS is usually attached to the side of the valve body inside the transmission, though on some vehicles it screws into the side of the case. It says P0849 is set when the "B" input does not match the normal operating voltages stored in the PCM/TCM's memory, here intermittently, and that while it is typically an electrical circuit issue, mechanical problems (internal leaks, cracked or missing check balls in the valve body, low line pressure or a stuck valve) can also set it and must not be overlooked, especially with an intermittent fault. RepairPal describes it more broadly: the PCM or TCM sets P0849 when it detects an issue with the hydraulic clutch or the pressure switch. Both sources agree on the name "Circuit Intermittent". It is a generic OBD-II code; OBD-Codes.com says it shows up more often on Nissan vehicles. Which sensor is "B" depends on the vehicle, so check a repair manual for yours. Its sibling codes for the same sensor are P0845 (circuit), P0846 (circuit range/performance), P0847 (circuit low) and P0848 (circuit high).

Q: Can I keep driving with P0849?

Stop and fix promptly. Get it diagnosed soon. RepairPal rates P0849 Urgent, meaning it can cause severe damage or be unsafe. OBD-Codes.com is milder: it says the PCM/TCM can compensate to some degree, though it may change how the transmission shifts or put it in limp mode (starting off in 2nd or 3rd gear). If shifting feels wrong or the car is stuck in one gear, drive gently and avoid highway and heavy-traffic driving until it's checked.

Reviewed 2026-10-24 · Based on 2 cited source(s)

What P0849 means

An automatic transmission uses fluid pressure to apply its clutches and change gears. A transmission fluid pressure sensor/switch (TFPS) turns that pressure into an electrical signal so the powertrain control module (PCM), or a separate transmission control module (TCM), can tell the operating pressure or when a shift is happening. OBD-Codes.com says the TFPS is usually attached to the side of the valve body inside the transmission, though on some vehicles it screws into the side of the case. It says P0849 is set when the "B" input does not match the normal operating voltages stored in the PCM/TCM's memory, here intermittently, and that while it is typically an electrical circuit issue, mechanical problems (internal leaks, cracked or missing check balls in the valve body, low line pressure or a stuck valve) can also set it and must not be overlooked, especially with an intermittent fault. RepairPal describes it more broadly: the PCM or TCM sets P0849 when it detects an issue with the hydraulic clutch or the pressure switch. Both sources agree on the name "Circuit Intermittent". It is a generic OBD-II code; OBD-Codes.com says it shows up more often on Nissan vehicles. Which sensor is "B" depends on the vehicle, so check a repair manual for yours. Its sibling codes for the same sensor are P0845 (circuit), P0846 (circuit range/performance), P0847 (circuit low) and P0848 (circuit high).

Severity: can I keep driving?

Stop and fix promptly

Get it diagnosed soon. RepairPal rates P0849 Urgent, meaning it can cause severe damage or be unsafe. OBD-Codes.com is milder: it says the PCM/TCM can compensate to some degree, though it may change how the transmission shifts or put it in limp mode (starting off in 2nd or 3rd gear). If shifting feels wrong or the car is stuck in one gear, drive gently and avoid highway and heavy-traffic driving until it's checked.

Common symptoms

Check engine light on (OBD-Codes.com)
Change in shift quality, or the transmission doesn't shift properly (both sources)
Car starts off in 2nd or 3rd gear because the transmission is in limp mode (OBD-Codes.com)
Increased fuel consumption (RepairPal)

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

Failed transmission fluid pressure sensor/switch (both sources; OBD-Codes.com rates it the likely cause)
Intermittent open, short to voltage or short to ground in the sensor signal circuit (OBD-Codes.com; RepairPal lists a wiring issue)
Corroded external connector terminals (OBD-Codes.com says this is the most common area of concern)
Internal mechanical transmission problem such as internal leaks, damaged check balls, low line pressure or a stuck valve (OBD-Codes.com rates it possible)
Low transmission fluid level (RepairPal)
Faulty PCM or TCM (both sources; OBD-Codes.com rates it unlikely and says a replacement must be programmed)
The sources differ: RepairPal adds low fluid level, while OBD-Codes.com focuses on the electrical circuit plus internal mechanical faults

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

Read all stored codes. If there are power-related codes or several pressure sensor codes, OBD-Codes.com says to diagnose those first.
Check for technical service bulletins (TSBs) for your vehicle; a known issue may have a known fix.
Check the transmission fluid level and condition.
Find the pressure sensor/switch connector and inspect the wiring for scraping, rubbing, bare wires, burn spots or melted plastic. Unplug it and look for burned or green, corroded terminals; clean them with electrical contact cleaner and a plastic brush, let them dry and apply electrical grease.
Clear the code and see if it comes back. If it doesn't, OBD-Codes.com says the connections were most likely the problem.

Typical fixes

Clean or repair corroded connectors and damaged or loose wiring
Top up the transmission fluid to the correct level
Replace the transmission fluid pressure sensor/switch
Repair internal transmission faults if the sensor and wiring check out
Replace and program the PCM/TCM only after other causes are ruled out

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

The transmission shifts badly, is stuck in limp mode or the code comes back after cleaning the connections
On many vehicles the sensor is mounted on the valve body inside the transmission, so replacing it means removing the transmission pan
OBD-Codes.com's circuit tests use a digital voltmeter and ohmmeter while wiggling the connections to catch the intermittent fault, and need the manufacturer's specifications: reference voltage is 12 volts or 5 volts depending on the vehicle, and sensor resistance varies by model
Checking for internal leaks, valve body problems or low line pressure needs transmission pressure testing
A replacement PCM/TCM must be programmed or calibrated to the vehicle

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Is P0849 serious?

It can be. RepairPal rates it Urgent. OBD-Codes.com says the computer can compensate to some degree, but shifting may change or the transmission may go into limp mode. Get it checked soon.

Can I keep driving with P0849?

Only gently and for short trips until it's diagnosed. If the car is stuck in one gear or shifts badly, avoid highway driving and get it looked at.

What does "intermittent" mean in P0849?

The fault comes and goes instead of being constant, which often points to a loose, corroded or chafed connection. OBD-Codes.com suggests wiggling the connector and wiring while testing to find it, and notes internal mechanical problems can also cause it.

What is the difference between P0845, P0846, P0847, P0848 and P0849?

All are for transmission fluid pressure sensor/switch "B". OBD-Codes.com lists P0845 as circuit, P0846 as circuit range/performance, P0847 as circuit low, P0848 as circuit high and P0849 as circuit intermittent.

How much does it cost to fix P0849?

Neither source gives a repair cost. It can range from cleaning a connector or adding fluid to replacing the sensor, transmission repair or the TCM, so get a diagnosis and a written estimate first.

Sources

Last reviewed 2026-10-24. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.