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Home / DTC / P0840 — Transmission Pressure Switch A

P0840 — Transmission Pressure Switch A

Detailed page for trouble code P0840.

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Code

P0840

LAND ROVER P — Powertrain

Transmission Pressure Switch A

Brand: LAND ROVER
Type: P — Powertrain
AI status
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ready
Completed 100%
Page language: EN

Causes

  • Faulty transmission pressure switch A
  • Open, shorted or high-resistance wiring between switch and PCM/TCM
  • Poor connector connection or corrosion at the switch or wiring harness
  • Low or contaminated transmission fluid causing abnormal pressure
  • Stuck valve or internal hydraulic problem in valve body or pump
  • Faulty PCM/TCM or incorrect module grounding/power supply

Symptoms

  • Check Engine / Transmission warning lamp illuminated
  • Erratic, harsh, delayed or slipping shifts
  • Transmission may enter limp/home mode with limited gear selection
  • Transmission temperature increase or failure to hold pressure
  • Stored or pending transmission-related DTCs and reduced drivability

What to check

  • Read and record freeze frame and all transmission-related codes with a scan tool
  • Inspect transmission fluid level and condition (color, smell, contamination)
  • Visually inspect switch connector and wiring for damage, corrosion, pin push-out or water intrusion
  • Wiggle-test harness while observing live data to see if signal drops out
  • Check for related codes (e.g., pressure switch B, TCM communication, range sensor)

Signal parameters

  • Consult OEM service data for exact values for your Land Rover model — values vary by model/year
  • Typical switch operation: two-state (open/closed) or voltage signal referenced to PCM (common: 0–5 V range)
  • Example generic behavior: switch closed = low/near 0 V or ground signal; switch open = near reference voltage (~5 V) — confirm with factory chart
  • Resistance across switch terminals may be near open/infinite in one state and low ohms in the other if switch is mechanical — check OEM spec

Diagnostic algorithm

  1. Connect a professional scan tool and record live transmission pressure switch A status and related parameters; clear codes and attempt to reproduce
  2. Perform a visual inspection of the switch, connector, and wiring harness for damage, corrosion, chafing, or oil contamination
  3. Check transmission fluid level and condition; correct level and fluid type if necessary
  4. Backprobe the switch connector with the ignition on (engine off) and measure reference voltage, signal voltage, and ground continuity—compare with OEM spec
  5. Wiggle wiring harness while watching live data to identify intermittent opens/shorts
  6. If wiring and connector tests are good, disconnect the switch and measure resistance or continuity of the switch itself; bench-test or substitute known good switch if available
  7. If the switch appears to operate but fault remains, perform a hydraulic pressure test with a calibrated gauge to confirm actual line pressure and correlate with switch behavior
  8. Inspect valve body and pump if pressure gauge shows incorrect pressure (may require transmission removal or specialist service)
  9. Repair or replace wiring, connector, or pressure switch as indicated; clear codes and road-test to verify repair; if repairs do not clear fault, consider module diagnostics or replacement as last resort

Likely causes

  • Damaged or corroded connector to the pressure switch
  • Broken or shorted signal/reference wire to PCM/TCM
  • Faulty pressure switch
  • Low fluid level or degraded fluid causing incorrect line pressure
  • Internal valve body or pump fault (less common than electrical causes)

Fault status

⚠️ Status
Transmission Pressure Switch A Circuit Malfunction — abnormal/open/shorted signal or incorrect pressure indication.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-4.0 hours

Similar codes

P0841 P0705 P0715 P0740 P0741 P0700
413

Browse 413 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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