Allison Fault Code

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SPN 191 FMI 9

Trans Warning.

Variant 1

System

Not specified

Symptom

Trans Warning.

Diagnosis & fix steps

LOGIC: Transmission Output Speed: Abnormal Update Rate. ACTION: Check the speed sensor on the output shaft; inspect wiring harness for frame rubs.

Red Seal field insights

Red Seal Fix: On vocational trucks, the output speed sensor gets hit by road debris or "wrapped" with wire/trash, breaking the connector.

Variant 2

System

Transmission

Symptom

Trans is in "Limp" (3rd Gear).

Diagnosis & fix steps

LOGIC: Transmission Output Shaft Speed - Missing Data. ACTION: Check the output speed sensor wiring at the tail-shaft of the trans.

Red Seal field insights

Specs: CAN-bus update rate error. RED SEAL FIX: On vocational trucks, this is usually a "pinched" harness from the body-builder installation.

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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