CAT Engine 7744 Fault Code: Secondary Throttle Position Sensor: Voltage Below Normal
Also called Accelerator Pedal Position #2 : Voltage Below Normal, Accelerator Pedsal Position #2 : Voltage Below Normal, Secondary Throttle Position Sensor - Voltage Below Normal, Secondary Throttle Position Sensor : Voltage Below Normal, Secondary Throttle Position Sensor voltage below normal, Secondary Throttle Position Sensor:Voltage Below Normal
Secondary Throttle Position Sensor: Voltage Below Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 7744 (SPN 29 / FMI 4) means the ECM has seen the secondary accelerator/throttle position sensor signal drop below its lower diagnostic limit for 1 second (some sensor variants use one second), after the ECM has been powered for 3 seconds. The engine switches to the primary throttle or drops to a limp home speed if no good throttle input is available. It affects C13, C15, and C18 engines.
Medium severity. The engine keeps running using the primary throttle or a limp home speed, so this is not an immediate shutdown event. But losing full throttle control can affect drivability and productivity, so it should be diagnosed the same shift it appears, especially if the primary throttle is also acting up.
What does CAT Engine error code 7744 mean?
Code 7744 points to the secondary throttle (accelerator pedal position #2, also called the secondary throttle position sensor) sending a voltage or duty cycle signal to the ECM that is below the expected normal range. This sensor is mounted on or attached to the throttle pedal assembly and reports pedal position back to the ECM so it knows how much engine speed the operator is requesting.
On engines with an analog sensor, the ECM sends it +5 V power and reads a raw voltage that should move between low idle and high idle, which the ECM then converts into a throttle position between 0% and 100%. On PWM-type sensor variants, the signal is a duty cycle instead of a straight voltage, with minimum duty cycle at pedal released and maximum duty cycle at pedal fully depressed.
Because this is the secondary throttle input, the engine has a built-in backup: if the primary throttle is healthy, the ECM just uses the primary and ignores the faulty secondary sensor. The problem becomes serious only if the primary throttle is also unavailable, since then the engine has no valid throttle signal at all and drops to limp home speed.
What triggers a CAT Engine 7744 code?
The ECM sets this code when the ECM has been powered for 3 seconds, diagnostic code 168-4 is not active, no 3510 (2131) codes are active, and the secondary throttle signal has been below the lower diagnostic limit for 1 second (stated elsewhere as one second). On PWM sensor variants, the same low-signal condition is detected through duty cycle dropping outside the expected range rather than a voltage reading.
Common causes of 7744
- Damaged, corroded, or abraded connectors or wiring at the sensor or ECM connector
- General problems with the wiring harness, including pinch points along the routing
- A faulty secondary throttle position sensor itself
- An intermittent connection or wiring fault that comes and goes with vibration or movement
- A faulty selector switch input feeding the secondary throttle circuit
- On some engine/ECM combinations, a faulty ECM or a faulty throttle assembly rather than just the sensor
How to troubleshoot CAT Engine 7744: first checks
- Connect an electronic service tool and check the input status of the secondary throttle position sensor live, since CAT specifically recommends this as the first diagnostic step
- Inspect the sensor connector and harness connectors for corrosion, abrasion, pinched wiring, or loose pins, being aware that terminal identification letters can vary by pedal manufacturer
- Trace the harness from the throttle pedal assembly back to the ECM looking for chafe points, pinches, or damage, especially near moving parts of the pedal assembly
- Check for other active codes tied to this fault, specifically 168-4/0168-01 (system voltage) and 3510 (2131)/0262 codes, since these must be inactive for 7744 to log and can point to a bigger power supply problem
- Confirm which throttle input (primary or secondary) is actually in control right now, since the engine may already be compensating and running normally on the other sensor
- Verify the sensor is receiving its expected power supply from the ECM and that the signal changes smoothly as the pedal is moved through its full travel
How the code clears
No separate clearing step is listed beyond repairing the wiring, connector, or sensor fault. Once the underlying problem is fixed, the ECM will keep ignoring inputs from the repaired throttle sensor until the keyswitch is cycled off and back on, so a keyswitch cycle after the repair is required before normal secondary throttle operation resumes.
Affected models and serial ranges
7744 appears in our records across 3 CAT Engine models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| 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 code 7744 mean?
It means the ECM detected that the secondary throttle position sensor's voltage (or duty cycle signal on PWM-style sensors) dropped below the normal expected range for at least 1 second, after the ECM had already been powered for 3 seconds. It is logged under SPN 29 / FMI 4.
Will my machine shut down if I get code 7744?
No. The engine is designed to keep running. If the primary throttle is working, the ECM simply uses the primary and ignores the faulty secondary sensor. Only if no functional throttle is available does the engine default to a limp home speed.
Can I still drive or operate with this code active?
Usually yes, since the primary throttle takes over. But if the primary throttle also has a fault, the engine will decelerate to (or hold at) the limp home speed and stay there until the code is cleared, so operation could be noticeably limited.
What usually causes code 7744?
Most cases trace back to wiring or connector problems: corrosion, abrasion, pinch points, or a bad harness. A faulty sensor, faulty selector switch input, faulty throttle assembly, or an intermittent connection are the other listed causes, and in some cases a faulty ECM.
Why does the fault come back after I fix the wiring?
Because the ECM continues to ignore inputs from the repaired throttle sensor until the keyswitch is turned off and back on again. If you don't cycle the key after the repair, the system may still act like the fault is active.
Is the secondary throttle sensor adjustable?
No. On the PWM-style sensor design, the throttle position sensor cannot be adjusted; its output range is fixed by the geometry of the pedal assembly itself.
Do I need a scan tool to diagnose this code?
CAT specifically recommends using an electronic service tool to check the input status of the throttle sensor live, since terminal identification and voltage/duty cycle behavior can be hard to judge without one.