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Home / DTC / P0735 — Gear 5 Incorrect ratio

P0735 — Gear 5 Incorrect ratio

Detailed page for trouble code P0735.

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P0735

MERCEDES-BENZ P — Powertrain

Gear 5 Incorrect ratio

Brand: MERCEDES-BENZ
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Worn or damaged fifth gear, synchromesh, or splines inside the gearbox
  • Faulty or sticking shift solenoid(s) controlling 5th gear
  • Mechatronic/valve body faults or internal hydraulic leaks
  • Low, contaminated, or incorrect transmission fluid
  • Faulty speed sensor (input/turbine or output/speed) or incorrect sensor signals
  • TCM/software adaptation or coding error

Symptoms

  • Check Engine / Transmission warning lamp illuminated
  • Harsh, delayed or missing shift into 5th gear
  • Engine RPM does not change proportionally to vehicle speed (incorrect ratio)
  • Vehicle may remain in lower gear or go into limp/safe mode
  • Unusual transmission noises when attempting 5th gear
  • Poor fuel economy at highway speeds if 5th gear is not engaged

What to check

  • Read and record all stored transmission and engine codes, including freeze frame data
  • Check live data: actual gear, requested gear, turbine/input speed and output speed (vehicle speed sensor)
  • Compare calculated gear ratio (engine RPM / output shaft RPM) against expected ratio for 5th gear
  • Inspect transmission fluid level, color, and smell; sample fluid if contamination suspected
  • Inspect wiring and connectors to mechatronic unit, solenoids and speed sensors for corrosion, damage or poor pins
  • Perform solenoid resistance and activation checks per factory procedure

Signal parameters

  • Requested/Selected gear (TCM gear request)
  • Actual/Current gear (TCM calculated gear)
  • Engine speed (RPM)
  • Input/turbine speed (transmission input sensor)
  • Output/vehicle speed sensor (transmission output speed)
  • Calculated gear ratio (engine or input speed ÷ output speed)

Diagnostic algorithm

  1. Verify the complaint and note when the fault occurs (cold/hot, load, speed). Retrieve all codes and freeze frame data.
  2. Check transmission fluid level, condition and service history. Top up or replace fluid if low/contaminated and clear codes to retest.
  3. Monitor live data during a road test: confirm requested gear vs actual gear, log engine RPM, input and output speeds, and calculate the ratio for 5th gear.
  4. If sensors show incorrect speeds, inspect and test input and output speed sensors and related wiring/connectors. Replace or repair as needed and retest.
  5. Test shift solenoids electrically (resistance, ground, supply) and command them using a diagnostic tool to verify operation. Repair wiring or solenoids as required.
  6. Check for mechatronic/valve body related faults and compare solenoid/pressure values to factory specs. If hydraulic pressures are out of range, investigate internal leaks or valve body failures.
  7. Review TCM software version, adaptations and coding. Perform adaptation/learn procedures or update software if a known issue exists.
  8. If electrical and external checks pass but ratio remains incorrect, consider internal mechanical inspection (drop pan, filter, inspect clutch packs, gearsets) or removal for rebuild/repair per Mercedes procedures.
  9. After repairs, clear codes, perform adaptation/learn and road test to confirm proper 5th gear engagement and no recurrence of P0735.

Likely causes

  • Shift solenoid for 5th gear sticking or electrical fault
  • Internal hydraulic leakage in the valve body/mechatronic unit
  • Worn clutch pack or gearset associated with 5th gear
  • Incorrect or low transmission fluid level or degraded fluid
  • Bad input or output speed sensor producing wrong ratio calculation
  • TCM software/adaptation values corrupted or incorrect transmission coding

Fault status

⚠️ Status
P0735: Transmission control module reports that the measured gear ratio for fifth gear is outside the expected limits. Possible causes include hydraulic leaks, faulty shift solenoid(s), damaged gear/clutch components, incorrect sensor signals, low/contaminated fluid, or TCM/software/adaptation issues.
🔴 Repair difficulty: Hard
⏱️ Diagnostic time: 3-8 hours
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