CAT Engine 7743 Fault Code: Secondary Throttle Position Sensor: Voltage Above Normal
Also called Accelerator Pedal Position #2 : Voltage Above Normal, Secondary Throttle Position Sensor - Voltage Above Normal, Secondary Throttle Position Sensor : Voltage Above Normal, Secondary Throttle Position Sensor voltage above normal, Secondary Throttle Position Sensor:Voltage Above Normal
Secondary Throttle Position Sensor: Voltage Above Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT fault code 7743 (SPN 29 / FMI 3) means the ECM sees the secondary accelerator pedal position sensor signal reading above its normal range. On C13, C15, and C18 engines, the ECM will switch over to the primary throttle if one is available, and if no functional throttle exists, the engine defaults to a limp home speed until the code is repaired and the keyswitch is cycled.
Medium severity. Not an immediate stop-the-engine issue since the ECM has a fallback to the primary throttle or limp home speed, but it does limit or alter engine speed control, which matters for productivity and safety in any application relying on responsive throttle input.
What does CAT Engine error code 7743 mean?
This code points to the secondary throttle position sensor, also called Accelerator Pedal Position #2, reporting a voltage that is too high for what the ECM expects during normal operation. The sensor is an analog device mounted to the throttle pedal or lever assembly and it sends a signal to the ECM that varies with pedal position, letting the ECM know how much engine speed the operator is requesting.
The sensor runs on 5 volts supplied by the ECM. As the pedal moves from released to fully depressed, the raw signal voltage should move smoothly within its expected range, and the ECM converts that into a throttle position between 0% and 100%. When the voltage reads above the upper limit the ECM has been programmed to accept, it flags 7743.
Because many CAT engines use a two-throttle strategy (primary and secondary, with input possibly overridden by a data link or PTO control), the ECM has built-in fallback logic. If the secondary throttle sensor fails, the primary throttle takes over. If neither throttle is usable, the engine drops to a limp home speed and stays there until the fault is fixed.
What triggers a CAT Engine 7743 code?
The ECM sets this code when it has been powered for 3 seconds, diagnostic code 168-4 is not active, no 3509 (262) codes are active, and the secondary throttle signal has been above the ECM's upper diagnostic limit for 1 second.
Common causes of 7743
- Damaged connectors or chafed, corroded, or broken wiring in the throttle sensor circuit
- A problem within the wiring harness between the sensor and the ECM
- A faulty secondary throttle position sensor itself
- An intermittent connection issue that only shows up under vibration, heat, or movement
- A faulty selector switch input feeding the throttle circuit
- A faulty foot pedal or hand lever assembly
- In rare cases, a faulty ECM
How to troubleshoot CAT Engine 7743: first checks
- Connect an electronic service tool and check the current input status of the secondary throttle sensor before disturbing anything.
- Inspect the pedal or lever assembly wiring harness end to end for damaged, pinched, or corroded connectors, paying attention that pin/terminal letters can vary by pedal manufacturer.
- With the key on and engine off, wiggle-test the harness and connectors near the pedal assembly while watching the service tool for voltage spikes or dropouts, since this can catch intermittent faults.
- Verify the ECM is supplying the correct 5 volt reference to the sensor at the connector.
- Check for other active codes such as 168-4 or 3509 (262) codes, since the ECM will not log 7743 if those are active; clearing those first may be necessary before this code can be properly diagnosed.
- Inspect the throttle pedal or lever assembly itself for mechanical binding or damage that could affect the sensor's travel range, keeping in mind the sensor cannot be adjusted.
How the code clears
No separate clearing step is listed beyond repairing the fault. Once the wiring, connector, sensor, or pedal assembly issue is corrected, the keyswitch must be cycled off and back on. Until that keyswitch cycle happens, the ECM will continue to ignore inputs from the repaired throttle even though the underlying problem is fixed.
Affected models and serial ranges
7743 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 7743 mean?
It means the ECM detected the secondary accelerator pedal position sensor (also called the secondary throttle position sensor) reporting a voltage above the normal expected range, corresponding to SPN 29 / FMI 3.
Will my engine still run with fault code 7743 active?
Yes, but engine speed control will be affected. If a primary throttle is available, the ECM switches to it. If no functional throttle is available, the engine defaults to a limp home speed and stays there until the fault is repaired.
Do I need to cycle the key after fixing the sensor or wiring?
Yes. Even after the repair is made, the ECM continues to ignore inputs from the repaired throttle until the keyswitch is turned off and back on.
Can I adjust the throttle position sensor to fix this code?
No. The throttle position sensor cannot be adjusted. Its output range is set by the geometry of the pedal or lever assembly, so if the range is wrong, the pedal assembly or sensor needs replacement, not adjustment.
Why does my machine feel like it's stuck at one engine speed?
This is the limp home speed behavior. When no throttle input is trusted by the ECM, it holds engine speed at a predetermined safe level and will not increase speed until the code is resolved.
Is 7743 the same as a primary throttle fault code?
No. This code is specific to the secondary throttle position sensor circuit. A separate but related fault exists for the primary throttle, and the ECM cross-checks both, meaning an active fault on one affects how the system handles the other.
What are the most common repairs for this code?
Damaged or corroded connectors, harness wiring problems, and a faulty sensor are the most frequently cited causes, with faulty selector switch input, faulty pedal or lever assemblies, and occasionally a faulty ECM also listed as possible causes.