Code
P0747
MERCEDES-BENZ
P — Powertrain
Pressure Control Solenoid Stuck On
Views:
UK: 30
EN: 50
RU: 36
AI status
Completed
Completed
100%
Causes
- Solenoid coil internally shorted or welded (electrically stuck on)
- Wiring short to constant battery voltage (power feed stuck on)
- Corroded/shorted connector or damaged harness
- Stuck or contaminated valve body spool (mechanically held on)
- Faulty transmission control module (TCM) or driver circuit
- Low or dirty transmission fluid causing valve sticking
Symptoms
- Harsh or erratic shifts, delayed engagement
- Torque converter lockup problems (stuck locked or not locking)
- Transmission slips under load or reduced engine power/limp mode
- Transmission fluid overheats or abnormal fluid pressure
- MIL (Check Engine Light) illuminated with P0747 stored
What to check
- Read freeze frame and full trouble code history with a capable scan tool
- Check live data: solenoid command vs actual pressure or TCM requested duty
- Visually inspect solenoid connector and wiring for corrosion, damage or pin migration
- Measure solenoid coil resistance with multimeter (unplugged)
- Perform an active test (command solenoid ON/OFF) and observe response
- Check transmission fluid level and condition for contamination or varnish
Signal parameters
- Supply voltage: ~12 V (battery) present at harness feed
- Control signal: PWM duty cycle 0–100% (varies by vehicle/TCM strategy)
- Typical coil resistance range: roughly 10–40 ohms (model dependent — consult factory spec)
- Expected current: typically
- When commanded OFF: control line should be low / open-circuit; when commanded ON: PWM or steady voltage applied by TCM
Diagnostic algorithm
- Retrieve all transmission/engine codes and freeze-frame data. Note any related codes (TCM, pressure sensor, other solenoids).
- Inspect wiring and connector at the transmission solenoid cluster for corrosion, pin damage, exposed conductors, or melted insulation. Repair any obvious damage.
- With ignition ON (engine off), measure voltage at the solenoid harness feed to confirm battery supply. Confirm ground reference at connector.
- Unplug solenoid, measure coil resistance to ground and between terminals. Compare to factory spec; a near-zero resistance to battery suggests short-to-power, infinite resistance suggests open coil.
- Using a scan tool with active test capability, command the solenoid ON and OFF while monitoring the control signal (duty) and hydraulic response (pressure or shift behavior). Note any lack of change when commanded.
- If the solenoid is electrically correct but remains active mechanically, suspect a stuck valve or contamination in the valve body. Inspect fluid for contamination and consider valve body disassembly or replacement of solenoid/valve body components.
- If wiring and solenoid are good but the solenoid is still being driven ON by the module, test the TCM output driver circuit for shorts. Substitute or bench-test TCM only after verifying wiring and solenoid condition.
- After repairs, clear codes and perform a road test and full transmission functional test. Re-scan to confirm code does not return and that system pressures/shift quality are restored.
Likely causes
- Short to battery on the solenoid circuit (connector/pin contact)
- Failed pressure control solenoid (coil or internal valve stuck)
- Valve body contamination or varnish holding spool in ON position
- Open/short in TCM driver causing improper command
- Poor ground connection or corroded connector at transmission
Fault status
Status
Pressure control solenoid stuck ON — solenoid circuit is continuously actuated or commanded high. Possible short to power, failed solenoid, stuck valve in valve body, or TCM driver fault. Inspect wiring, connector, fluid condition, and solenoid operation before replacing control module.
Repair difficulty: Medium
Diagnostic time: 2-4 hours
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