P0842
Transmission Fluid Pressure Sensor/Switch A Circuit Low
Transmission / hydraulic control
Generic OBD-II
Medium
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.
Medium
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.
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?+
Only briefly and gently. Erratic line pressure and limp mode can accelerate transmission wear, so get it diagnosed promptly.
Can I just clear P0842?+
It clears, but returns quickly unless the sensor, wiring, or fluid problem is corrected.
Related codes
Often seen with P0842
Read & clear P0842 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX