Allison Fault Code

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P0752 / DTC 52-21

Stuck in 2nd or 3rd / Range Inhibit

System

Shift Solenoid

Symptom

Stuck in 2nd or 3rd / Range Inhibit

Diagnosis & fix steps

LOGIC: Shift Solenoid 1 (SS1) Valve Performance - Stuck On. ACTION: Drop the main valve body oil pan. Remove the SS1 solenoid; inspect the internal valve bore for sticky varnish or aluminum machining debris. Test coil resistance (spec: ~20–30Ω) and verify spool strokes freely.

Red Seal field insights

Mechanical Sticking: High-temperature oxidation bakes fine clutch silt onto the solenoid sliding spool, mechanically holding it open even when the TCM drops electrical current.

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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