OBD-II trouble code
P0843: Transmission Fluid Pressure Sensor/Switch "A" Circuit High
The transmission fluid pressure sensor or switch 'A' is sending a signal that's too high — a high voltage the control module reads as out of range. Usually an open circuit or wiring problem rather than an actual pressure issue.
Quick facts
- System
- Powertrain
- Category
- Transmission / Pressure Control
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $120 – $600
- DIY difficulty
- Intermediate DIY
What does P0843 mean?
P0843 sets when the transmission control module (TCM) or PCM reads the signal from transmission fluid pressure sensor/switch "A" as too high — a voltage above the expected range. This sensor reports internal hydraulic pressure so the module can verify clutch apply and time its shifts. "Circuit High" describes a high signal voltage, which usually reflects an electrical fault rather than genuinely high pressure.
The most common causes are an open circuit or a short to voltage. When the signal wire opens, loses its ground, or shorts to a power source, the reading floats or spikes high and the module flags P0843. As with the low-side code, the transmission connector's harsh environment makes corrosion, loose pins, and chafed wiring frequent culprits, and a sensor that has failed internally can latch the signal high.
It's rare for P0843 to represent truly excessive line pressure — a stuck pressure control solenoid or valve-body fault could raise pressure, but that scenario is uncommon and usually brings other codes and symptoms along with it. In most cases, a high reading means the module isn't getting a valid signal. Diagnosis focuses on the wiring, the connector, the sensor's ground and reference, and the sensor itself, with an actual line-pressure check available as a tie-breaker if the electrical side looks clean.
Common causes
- Open circuit in the pressure sensor signal or ground wire
- Short to voltage in the sensor circuit
- Corroded, loose, or damaged transmission connector
- Failed transmission fluid pressure sensor/switch A
- Lost or high-resistance sensor ground
- Rarely, genuinely high line pressure from a stuck solenoid or valve-body fault
Symptoms
- Check engine light on with P0843 stored
- Harsh or poorly timed shifts
- Transmission entering limp mode in some cases
- Erratic shift behavior
- Often no strong driveability symptoms if pressure is actually fine
Diagnostic steps
- 1.Scan for companion codes to see whether other transmission faults accompany the high reading.
- 2.Inspect the transmission connector and sensor wiring for corrosion, opens, and shorts to power.
- 3.Back-probe the sensor signal and check the voltage against specification with the key on.
- 4.Verify the sensor ground and reference voltage — a lost ground often reads as a high signal.
- 5.Substitute or bench-test the pressure sensor if the wiring checks out.
- 6.If the electrical side is clean, measure actual line pressure with a gauge to rule out a genuine hydraulic cause.
Repair cost
$120 – $600
A wiring or connector repair is often $100-$250. Replacing the transmission fluid pressure sensor runs roughly $150-$450 depending on whether it's externally mounted or inside the pan on the valve body. A genuine over-pressure cause is uncommon; if found, the cost follows the solenoid or valve-body repair required.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with transmission shift solenoid replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.