Transmission Fluid Pressure Sensor/Switch A Circuit Low
What it means
P0842 means the transmission fluid pressure (TFP) sensor/switch 'A' circuit is reading an abnormally low voltage. That sensor tells the transmission controller the hydraulic pressure inside the gearbox; when its signal is out of range the transmission can shift harshly, slip, or default to a protective limp mode.
Can I keep driving? Engine starts, but expect harsh or delayed shifts and possibly limp mode — drive gently and repair soon to avoid transmission wear.
Real-world scan data
Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.
Common symptoms
What you'll notice
- Harsh or delayed shifting
- Transmission slipping or not engaging properly
- Reduced acceleration or a 'limp mode' feel
- Check-engine light on
Common causes
Most likely first
- Short to ground or open in the TFP sensor 'A' wiring/connectorLikely
- Faulty transmission fluid pressure sensor/switch ACommon
- Low or contaminated transmission fluid affecting pressureCommon
- Poor connection at the sensor, or (less often) the transmission control moduleLess often
How to diagnose & fix
Work through it in order
- Check transmission fluid level and condition first — low or degraded fluid is cheap to rule out.
- Read freeze-frame data and inspect the sensor connector and wiring for a short to ground or open.
- Back-probe the sensor and compare its reading against known pressure specs with the engine running.
- Replace the TFP sensor/switch A if it fails testing; repair wiring as needed, then clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0842?+
Can I just clear P0842?+
Related codes
Read & clear P0842 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.