Code
P0746
MERCEDES-BENZ
P — Powertrain
Pressure Control Solenoid Performance or Stuck Off
Views:
UK: 17
EN: 31
RU: 31
AI status
Completed
Completed
100%
Causes
- Faulty transmission pressure control solenoid (electrical or mechanical failure)
- Open, shorted or intermittent wiring/connectors to the solenoid (corrosion, broken wire, poor pin seating)
- Low, contaminated, or degraded transmission fluid (debris/clutch material blocking valve)
- Stuck valve or contamination in the valve body
- Faulty transmission control module (TCM) or PCM driver circuit (less common)
- Poor ground or battery/charging system issues affecting solenoid drive voltage
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine light on
- Harsh, delayed or erratic shifting
- Transmission slipping or inability to achieve/maintain proper gears
- Limp-home mode or reduced transmission functionality
- Unusual transmission noise or inability to lock torque converter
- Shift flare, flare on upshift or downshift
What to check
- Read freeze frame and all stored transmission codes; note conditions (temp, throttle, RPM)
- Check transmission fluid level and condition (color, smell, metal particles)
- Inspect wiring and connectors at the transmission for corrosion, broken wires or poor pin fit
- Back-probe solenoid connector while commanding solenoid on/off with a scan tool and observe voltage/duty
- Measure solenoid coil resistance and continuity to ground per service manual
- Check grounds and battery voltage under load
Signal parameters
- Solenoid coil resistance: typically varies by model — commonly in the range of ~10–40 Ω (consult factory spec)
- Drive voltage: 0–12 V (solenoid is often PWM-driven; raw battery voltage present when commanded)
- Duty cycle: 0–100% (active control will vary PWM duty; expected changes when ECU commands pressure adjustments)
- PWM frequency: varies by manufacturer — often tens to a few hundred Hz (check factory spec)
- Line pressure response: line pressure should increase/decrease as commanded duty changes; lack of change indicates hydraulic or solenoid failure
Diagnostic algorithm
- Read and record all codes and freeze frame data. Check for related transmission codes and stored history.
- Verify fluid level and condition. If fluid is low or heavily contaminated, top up and consider fluid/filter service before further testing.
- Visually inspect wiring harness and connector at the transmission solenoid for damage, corrosion, pushed-out pins, or poor seals. Repair any issues.
- With ignition on (engine off), disconnect connector and measure solenoid coil resistance; compare to spec. Check for short to ground or open circuit.
- Back-probe connector with a lab scope or scan tool while commanding solenoid ON/OFF. Confirm presence of proper voltage and expected PWM/duty changes from the PCM/TCM.
- While commanding the solenoid, monitor line pressure (if vehicle supports PID) or road-test and monitor shift quality for change. No pressure response suggests hydraulic/valve-body issue.
- Wiggle-test wiring while monitoring live data to check for intermittent faults. Test battery/charging voltage and transmission grounds.
- If electrical tests pass but solenoid does not actuate or valve is suspected stuck, drop pan and inspect for metal debris, magnet, clogged screens, or valve body contamination. Clean or replace valve body/solenoid as required.
- If valve body/solenoid replacement is performed, use correct OEM parts and follow torque/assembly/bleeding procedures. Reprogram or update TCM software if required by service bulletin.
- Clear codes and perform road test under conditions that initially set the code. Re-scan to confirm issue resolved.
Likely causes
- Damaged/contaminated pressure control solenoid
- Wiring harness connector fault at transmission (pin corrosion, loose connector)
- Debris or varnish in valve body preventing valve movement
- Low or dirty transmission fluid reducing hydraulic response
- Intermittent PCM/TCM driver output or internal ECU fault (rare)
Fault status
Status
P0746 — Transmission Pressure Control Solenoid Performance/Stuck Off: The transmission control module detected the pressure control solenoid is not responding as commanded (electrical fault, stuck valve, or hydraulic contamination), which can cause incorrect line pressure and shifting problems.
Repair difficulty: Medium
Diagnostic time: 1.5-4.0 hours
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