What it means
The transmission fluid pressure sensor A circuit reports voltage below threshold, indicating short to ground or sensor failure.
At a glance
- Usually lights the check-engine light
How it works
Transmission pressure sensor or switch A sends a signal voltage that the control module uses to assess hydraulic pressure. P0842 sets when the A circuit voltage falls below its calibrated threshold, pointing toward a low signal such as a short to ground, a failed sensor, or a poor connector connection.
Common causes
Most likely first.
- Signal shorted to ground
- Sensor failed
- Connector pins corroded - high contact resistance
Symptoms
- Transmission warning light may be on
- Shifting may be abnormal
How to diagnose it
- Record freeze-frame data and check sensor A live voltage or pressure data for a low or implausible reading when the code is present.
- Inspect sensor A’s connector and harness for corrosion, fluid intrusion, damaged insulation, or a signal wire contacting ground.
- With the wiring diagram, check the sensor A reference supply and ground before testing the signal wire for a short to ground.
- Test the sensor A signal and connector terminals against the manufacturer’s specification, including whether the reading changes as expected under the specified conditions.
- If the harness checks out, test or substitute sensor A only as allowed by the vehicle’s service procedure to confirm an internal sensor fault.
Common fixes
- Clean and secure corroded or loose sensor A connector terminals where repair is permitted.
- Repair a signal wire shorted to ground or other damaged wiring in the A circuit.
- Replace sensor A if its output remains below specification with a sound supply, ground, and harness.
- Repair any fluid intrusion source that is damaging the connector.
Can I keep driving?
A low A-circuit signal can lead to abnormal shifting or a transmission warning, so avoid towing, hard acceleration, and long trips until it is checked. Stop driving if the transmission slips, loses drive, or shifts severely harshly, because continued operation may cause damage.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.