CAT 01 Fault Code: Idle Shutdown Override
Idle Shutdown Override · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 01, SPN 592 / FMI 31, means the ECM logged an Idle Shutdown Override event. This happens when the idle shutdown timer is close to expiring and the operator or a temperature setting overrides the shutdown, or when a related switch or sensor changes state during that window. It is mostly an informational/logging code tied to fuel-economy idle management, but it can point to a bad brake, clutch, PTO, or speed sensor if it shows up unexpectedly.
Low severity. This code is largely informational and tied to the idle shutdown timer feature rather than engine damage. Treat it as Low severity unless it keeps recurring, which suggests a real sensor or switch fault worth chasing down.
What does CAT error code 01 mean?
CAT code 01 fires when the Engine Control Module (ECM) sees an idle shutdown override condition. There are two basic triggers described by CAT: either the 'Allow Idle Shutdown Override' parameter is set to 'Yes' and the brake switch or clutch switch changes status, or that parameter is set to a temperature-based mode ('J1587 Outside Temp Based' or 'Outside Temperature Based') and the outside temperature is above the programmed maximum or below the programmed minimum.
The idle shutdown timer itself is a fuel-saving feature. It is a customer-programmable value that can be set anywhere from 3 minutes to 1440 minutes. The timer runs whenever vehicle speed is zero, the engine is not in cold mode or dedicated PTO mode, and the engine is not under load, regardless of whether the parking brake is set.
The check engine lamp begins rapid flashing in the final 90 seconds before the programmed shutdown time expires. During that 90 second window, depressing the clutch pedal or the service brake pedal can disable the timer. The timer can also be reset any time by moving the vehicle or by quickly tapping the accelerator pedal.
What triggers a CAT 01 code?
The ECM sets this code when the idle shutdown timer is within the final 90 seconds before it is set to expire, and the 'Idle Shutdown Time' parameter is programmed to at least 3 minutes, combined with either an override permission set to 'Yes' with a brake or clutch switch state change, or an override permission set to a temperature-based mode with the outside temperature above the programmed maximum or below the programmed minimum.
Common causes of 01
- ECM idle shutdown parameters not programmed properly (override permission or idle shutdown time not set as intended)
- Failed or misadjusted service brake pedal position switch, or a wiring/harness fault to that switch
- Failed or misadjusted clutch pedal position switch, or a wiring/harness fault to that switch
- Vehicle speed sensor or speedometer reading incorrectly, or a related wiring fault
- PTO switch or PTO harness failure
- An active vehicle speed signal fault code, which will prevent the idle shutdown timer from working at all
How to troubleshoot CAT 01: first checks
- Check for any active vehicle speed sensor or speedometer-related fault codes first. If one is active, the idle shutdown timer cannot function correctly and needs to be resolved before this code will clear.
- Verify the ECM programming for 'Allow Idle Shutdown Override' and 'Idle Shutdown Time' parameters match what the fleet or owner actually wants configured.
- Inspect the service brake pedal position switch and its wiring for corrosion, loose pins, or damage.
- Inspect the clutch pedal position switch and its wiring, if the vehicle is equipped with one.
- Inspect the PTO switch and associated harness for damage or poor connections.
- Confirm the vehicle speed sensor is reading accurately by comparing it against a known-good reference while road testing, if possible.
How the code clears
No separate clearing step is listed beyond correcting the underlying cause. Once the ECM parameters are set correctly and any faulty brake, clutch, PTO, or speed sensor circuits are repaired, the override condition should stop recurring and the code should not log again under normal idling.
Affected models and serial ranges
01 appears in our records across 4 CAT models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C11 | Serial range not listed in source records |
| C13 | Serial range not listed in source records |
| C15 | Serial range not listed in source records |
| C18 | Serial range not listed in source records |
Frequently asked questions
What does CAT fault code 01 mean?
It means the ECM detected an Idle Shutdown Override event. This is tied to the idle shutdown timer feature, which is meant to limit unnecessary idling for fuel economy. The override can be triggered by a brake or clutch switch change, or by an outside temperature reading outside the programmed range.
Is CAT code 01 serious?
Generally no. It is mostly an informational code related to how the idle shutdown timer feature is configured and used. It becomes worth investigating only if it recurs often or is accompanied by other codes for the vehicle speed sensor, brake switch, or clutch switch.
Why does my truck's idle shutdown timer not seem to work?
If there is an active fault code for the vehicle speed signal, the idle shutdown timer will not activate. Check for vehicle speed sensor issues first. Also confirm the idle shutdown time parameter is actually programmed, since it must be set to at least 3 minutes for the timer logic to run.
How long can the idle shutdown timer be set for?
CAT allows the Idle Shutdown Time parameter to be programmed anywhere from 3 minutes to 1440 minutes, depending on customer preference.
What happens right before the idle shutdown timer expires?
The check engine lamp starts flashing rapidly during the final 90 seconds before the programmed shutdown time is reached. During that window, pressing the clutch pedal or the service brake pedal can disable the timer, or the driver can reset it earlier by moving the vehicle or briefly tapping the accelerator.
Can a bad brake or clutch switch cause code 01?
Yes. If the 'Allow Idle Shutdown Override' parameter is set to 'Yes', any change in status of the brake switch or clutch switch during the timer window can trigger this code. A failed switch or damaged wiring to either switch is a listed possible cause.
Does outside temperature affect this code?
It can, if the override parameter is programmed to a temperature-based mode. In that case, the code sets when the outside temperature reads above the programmed maximum or below the programmed minimum threshold.