Transmission Fluid Pressure Sensor/Switch B Circuit Intermittent
The P0849 code means the vehicle's onboard diagnostic system has detected: Transmission Fluid Pressure Sensor/Switch B Circuit Intermittent. This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- hard
- Estimated cost
- $150 - $800 (parts and labor)
Read and clear transmission codes. Many trans codes are caused by low or burnt fluid -- check level and color before assuming the worst.
Basic scanners only read engine codes. This reads transmission, ABS, and airbag too.
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Common Symptoms
- Check Engine Light on
- Intermittent harsh shifting
- Transmission pressure reading drops out
- Occasional shift quality issues
Probable Causes (Ranked by Likelihood)
- Loose connector at transmission fluid pressure sensor B Very High
- Intermittent wiring break in pressure sensor B circuit High
- Pressure sensor B with marginal internal connection Moderate
- Transmission fluid contamination affecting sensor Moderate
Frequently Asked Questions
What causes intermittent transmission pressure sensor issues?
The most common cause is a loose or corroded connector. Transmission sensors operate in a high-vibration, high-temperature environment that degrades connections over time.
Can contaminated fluid cause intermittent sensor readings?
Yes. Metallic debris in old transmission fluid can create intermittent electrical paths or block pressure passages, causing erratic sensor readings.
Should I change the fluid when replacing a pressure sensor?
Yes. If the fluid is contaminated, the debris can damage the new sensor. A fluid change also removes contaminants that may have contributed to the original sensor failure.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
-
Wiggle the pressure sensor B connector while monitoring signal with scan tool
-
Inspect sensor wiring for intermittent breaks, especially at connectors
-
Monitor pressure sensor B data over extended driving to capture dropouts
-
Check transmission fluid condition; debris can affect sensor readings
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
Commonly Affected Vehicles
- 2010-2020 Ford F-150
- 2012-2019 Chevrolet Silverado
- 2011-2020 Toyota Camry
- 2009-2019 Honda Accord
Related Codes
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