P0849: Transmission Fluid Pressure Sensor/Switch B Circuit Intermittent

Transmission fluid pressure sensor/switch A and B are inputs inside the automatic gearbox. A switch only reports pressure present or absent, a sensor reports a value. The letter is the maker's choice: Allison 1000 uses A and B for the switches on shift valves S1 and S2, GM's CVT for the primary and secondary pulley sensors, GM's 2025 8-speed A for the lube pressure sensor; Ford reports pressure faults under its solenoid codes instead. P0849 reports short dropouts of the B signal. GM bulletin 21-NA-033 for the Corvette C8 dual clutch lists it with P0841, P0844 and P0846: first the valves are cleaned and the clutches relearned, and only if the code comes back on its own is the circuit traced. Like the A counterpart P0844 it has no published thresholds.

Symptoms

• Warning lamp coming and going
• Occasional shift shocks
• Brief limp mode

Most likely causes

• Loose contact or corrosion at the gearbox connector or control unit
• Dirt in valve or sensor causing signal jumps
• Sensor faulty internally
• Chafed spot in the harness

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the fluid level and condition
2. Gently move the wiring with the engine running and watch whether the reading changes.
3. Read the input and output speed in live data
4. Check the connector and wiring
5. Check for other related engine codes
6. Consult the manufacturer's procedure for the transmission

Good to know

• Repair difficulty: medium
• It can trigger limp mode.
• It affects emissions.

What each character of P0849 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 8: Transmission
• 49: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0849?

Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.

What causes code P0849?

The most common causes are: loose contact or corrosion at the gearbox connector or control unit; dirt in valve or sensor causing signal jumps; sensor faulty internally.

Related codes

• P0845Transmission Fluid Pressure Sensor/Switch B Circuit
• P0846Transmission Fluid Pressure Sensor/Switch B Circuit Range/Performance
• P0847Transmission Fluid Pressure Sensor/Switch B Circuit Low
• P0848Transmission Fluid Pressure Sensor/Switch B Circuit High
• P0844Transmission Fluid Pressure Sensor/Switch A Circuit Intermittent

Sources

• static.nhtsa.gov: MC 10217091 0001
• static.nhtsa.gov: MC 10212566 9999
• law.cornell.edu: 13 CCR 1968.2

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.