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Home / DTC / P1734 — Line pressure system fail(A)

P1734 — Line pressure system fail(A)

Detailed page for trouble code P1734.

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Code

P1734

MITSUBISHI P — Powertrain

Line pressure system fail(A)

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

Causes

  • Low or degraded transmission fluid level or quality
  • Faulty line pressure sensor (pressure transducer) or incorrect sensor signal
  • Faulty line pressure control solenoid / regulator valve
  • Wiring harness damage, poor connector contacts or short to battery/ground
  • Faulty transmission control module (TCM) or incorrect software/calibration
  • Mechanical problems: failing oil pump, worn clutch packs, blocked passages in valve body

Symptoms

  • Check Engine / Transmission warning light set
  • Harsh, delayed, or erratic upshifts or downshifts
  • Transmission slipping, inability to hold gear under load
  • Reduced power or limp-home mode engaged
  • Unusual transmission noise (whine or groan)
  • Transmission overheating or high fluid temperature

What to check

  • Read freeze frame data and live PIDs with a capable scan tool (line pressure, solenoid status, gear, engine load, temperature)
  • Verify transmission fluid level and condition (color, smell, contamination) when warm on level ground
  • Inspect wiring and connectors at the pressure sensor, solenoids and TCM for damage, corrosion or loose pins
  • Check for other transmission codes and related engine codes
  • Perform basic electrical checks: battery voltage and ground integrity (low voltage can affect solenoids)
  • If available, perform a pressure gauge test at the manufacturer pressure tap to compare commanded vs actual pressure

Signal parameters

  • Line pressure sensor typical electrical range ~0.5–4.5 V (manufacturer-specific)
  • Commanded line pressure should change with throttle/load and with solenoid activation
  • Solenoid control: PWM frequency and duty cycle vary by manufacturer — duty should change when TCM commands pressure variation
  • When idle and park, commanded base pressure is lower; under wide open throttle commanded pressure increases to maintain clutches

Diagnostic algorithm

  1. Retrieve codes, freeze frame and live data; note operating conditions when fault set. Clear code and perform road test while monitoring line pressure-related PIDs. 2) Check transmission fluid level/condition and correct if required. Replace fluid/filter if contaminated and retest. 3) Visually inspect wiring harnesses and connectors at the pressure sensor, solenoids and TCM. Repair any damaged wiring or poor connections. 4) Using a scan tool, command line pressure solenoid(s) (or solenoid A/B) and observe PIDs for response. Check solenoid resistance against spec and check for short to power/ground. 5) If electrical operation appears correct, install a mechanical hydraulic pressure gauge at the service port to compare actual pressure to commanded values at idle, partial throttle and full throttle. Document discrepancies. 6) If mechanical pressure is low while electrical commands are correct, inspect/repair valve body (clean or replace regulator valve/solenoid) and check pump output; replace worn pump or valve body as needed. 7) If electrical/sensor faults persist and wiring and solenoids test good, consider replacement or reflashing of the TCM following manufacturer procedures. 8) After repairs, clear codes and verify proper operation through road testing and rechecking live data.

Likely causes

  • Low fluid level or contaminated fluid causing weak pressure
  • Open/short/poor connection at pressure sensor or solenoid connector
  • Pressure sensor out of range (internal failure)
  • Stuck/contaminated pressure control valve or failed solenoid coil
  • Internal transmission wear (pump/valve body) reducing achievable pressure
  • TCM fault or corrupted adaptive values

Fault status

⚠️ Status
Line pressure control system malfunction detected. Actual hydraulic pressure does not meet commanded values or control circuit fault present.
🔴 Repair difficulty: Hard
⏱️ Diagnostic time: 2-6 hours

Similar codes

P0740 P0750 P0760 P0730 P1762
406

Browse 406 MITSUBISHI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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