P0840
PowertrainTransmission Pressuremoderate severityTransmission Fluid Pressure Sensor/Switch A Circuit
What P0840 Means
The PCM detected a problem in the transmission fluid pressure sensor or switch circuit A. This can cause incorrect line pressure readings and affect shift quality.
Symptoms
- Harsh or erratic shifting
- Transmission warning light on
- Possible limp mode
Common Causes
- Faulty transmission fluid pressure sensor
- Damaged wiring or connector
- Low or dirty transmission fluid
- Internal transmission pressure fault
Diagnostic Steps
- Scan for codes and check freeze frame data
- Check transmission fluid level and condition
- Inspect sensor wiring and connector
- Test sensor resistance and compare to spec
🔌 Don't have a code reader?
Any of these will read and clear this code — pick by how deep you want to go.
Budget handheld~$40
ANCEL AD410 →
No-phone-needed handheld — reads, clears, live data, freeze frame.
✓ ANCEL official store
Serious DIY~$100
BlueDriver Pro →
Enhanced codes (ABS, airbag, TPMS) plus repair reports.
SHOP FAVORITEShop-grade tablet~$300
Autel MaxiCOM MK808S →
Bidirectional tests, service resets, all systems.
✓ Autel official store
Pro diagnostics$1,500+
Autel MaxiSys MS906 Pro →
Full-system pro platform — topology mapping, ECU coding, the works.
✓ Autel official store
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Community Confirmed Fixes
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