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CID 0091 FMI 08

Engine stuck at idle; No throttle response; "Limp Home" mode.

System

Caterpillar (ECM)

Symptom

Engine stuck at idle; No throttle response; "Limp Home" mode.

Diagnosis & fix steps

Throttle Position Sensor - Abnormal Signal. LOGIC: The ECM is receiving a PWM (Pulse Width Modulated) signal that is "noisy" or has an incorrect frequency. ACTION: 1. Check the harness at the base of the accelerator pedal. 2. Verify 5V/8V supply to the sensor. FIX: Replace the Throttle Position Sensor or repair the "rub" in the cab-to-engine harness.

Red Seal field insights

The 8V Secret: Most CAT throttle sensors run on 8 Volts, not 5V. If you measure 5V, you have a short in the harness. Also, check for floor mat interference; if the pedal can't return to the absolute "0" position, the ECM will throw this code for safety.

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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