GM Fault Code

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P0746

Harsh Clunk on Shift / Stuck in 3rd Limp

System

Pressure Control

Symptom

Harsh Clunk on Shift / Stuck in 3rd Limp

Diagnosis & fix steps

LOGIC: Pressure Control Solenoid 1 (PCS1) Performance / Stuck Off. ACTION: Disconnect the external round 20-way chassis harness plug at the rear of the transmission. Test PCS1 resistance across pins E and F (spec: ~3–6Ω). If resistance is correct, inspect the main pressure regulator valve bore inside the front pump housing for scoring.

Red Seal field insights

Pump Bore Scoring: The hardened steel pressure regulator valve oscillates inside the softer aluminum pump body bore. Over thousands of hours, the bore wears out-of-round, causing the valve to hang and dumping mainline hydraulic pressure.

Same code keeps coming back?

That's a program problem, not a part problem. Book a 30-minute uptime review with Grant, a Red Seal Heavy Duty Technician.

Book an uptime review

Read before you touch anything

  • This is general reference information, not a repair manual. It is for trained, qualified technicians.
  • Fault codes, meanings and procedures vary by model, serial number and software version. Confirm the code and the procedure against the manufacturer's service manual before acting.
  • Follow the OEM service manual, torque specs and your site's safety procedures: lockout/tagout, block raised equipment, relieve hydraulic, fuel and air pressure, and let hot systems cool.
  • You use this information at your own risk. Adventure Mechanical and AM Fleet Integrity accept no liability for damage, injury, downtime or loss arising from its use.
  • Not affiliated with or endorsed by any manufacturer. Brand names are used only to identify the equipment a code applies to.

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