CAT Engine 3428 Fault Code: Secondary Engine Speed Sensor : Abnormal Frequency, Pulse Width, or Period
Also called Engine Speed Sensor #2 : Abnormal Frequency, Pulse Width or Period, Engine Speed Sensor #2 : Abnormal Frequency, Pulse Width, or Period, Secondary Engine Speed Sensor - Abnormal Frequency, Pulse Width, or Period, Secondary Engine Speed Sensor : Abnormal Frequency Pulse Width, or Period, Secondary Engine Speed Sensor Abnormal Frequency, Pulse Width, or Period, Secondary Engine Speed Sensor abnormal frequency, pulse width, or period, Secondary Engine Speed Sensor: Abnormal Frequency, Pulse Width, or Period
Secondary Engine Speed Sensor : Abnormal Frequency, Pulse Width, or Period · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 3428, SPN 723 FMI 8, means the ECM lost the signal from the secondary engine speed/timing sensor for at least 2 seconds while the primary sensor signal stayed valid, with the engine already running past 3 seconds. It will not stop a running engine by itself, but it will prevent a stopped engine from restarting until fixed.
High severity. The engine keeps running on the primary sensor alone if this fault sets while operating, so performance is largely unaffected in that moment. But once the engine is shut off with this fault present, it will not restart. If both speed/timing signals are ever lost at the same time, the ECM terminates fuel injection and shuts the engine down. Treat this as a stop-soon issue, not a stop-now emergency, unless the engine has already stalled.
What does CAT Engine error code 3428 mean?
This code applies to CAT C13, C15, and C18 engines and points to the secondary engine speed/timing sensor circuit. The engine uses two speed/timing sensors: a primary sensor near the flywheel housing that reads the crankshaft timing ring, and a secondary sensor that reads camshaft or fuel pump drive gear position depending on engine family. The ECM uses these signals together to know crankshaft position and engine rpm, and to establish correct injector firing order and timing.
Under normal running, the secondary sensor is mainly used to find the number 1 cylinder position for starting, then the primary sensor takes over for engine speed. If the secondary signal drops out while the engine is already running, there is generally no noticeable performance change because the ECM keeps using the primary sensor. But the secondary sensor is required for starting: if its signal is missing at start-up, the engine may take longer to start or run rough for a few seconds while the ECM sorts out firing order using the primary sensor alone.
If the secondary signal is lost while the engine is stopped, the engine will not restart. And if both the primary and secondary signals are lost at the same time during operation, fuel injection is terminated and the ECM shuts the engine down. This is why a 3428 code should not be ignored even though the engine may seem to run fine at first.
What triggers a CAT Engine 3428 code?
The ECM sets this code when the secondary speed/timing sensor signal is lost or intermittent for at least 2 seconds while the primary speed/timing sensor signal remains valid and the engine is running, and the engine has already been running for more than 3 seconds. On some versions this also requires that diagnostic code 0168-01 is not active and that no 0041 diagnostic codes are active.
Common causes of 3428
- Damaged connectors and/or wiring at the secondary speed/timing sensor circuit
- A general problem with the wiring harness
- A faulty secondary sensor or sensor assembly
- Damaged crankshaft or camshaft timing ring
- Incorrect timing of the fuel pump (affects engines where the secondary sensor reads fuel pump drive gear movement)
- A faulty ECM
How to troubleshoot CAT Engine 3428: first checks
- Inspect the secondary speed/timing sensor connector and wiring for corrosion, damage, or loose pins before doing anything else.
- Check the harness routing between the sensor and the ECM for chafing, pinches, or heat damage.
- On engines where the sensors are interchangeable, swap the primary and secondary sensors to see if the fault follows the sensor. On engines where the two sensors are not interchangeable, do not swap sensor positions, since they use different sensor types and this test does not apply.
- Confirm no other active codes are masking or interacting with this one, since some versions of this diagnostic require code 0168-01 and 0041 codes to be inactive before 3428 will set.
- Check fuel pump timing where applicable, since incorrect fuel pump timing is listed as a possible cause on some C13/C15/C18 configurations.
- Inspect the crankshaft or camshaft timing ring for physical damage that could disrupt the sensor's pulse pattern.
How the code clears
No separate clearing step is listed beyond correcting the underlying cause. Once the wiring, connector, sensor, timing ring, fuel pump timing, or ECM issue is repaired, the code should stop being active and the engine should restart normally. If the engine is currently stopped and won't restart because of this fault, the underlying sensor signal problem must be resolved first since loss of the secondary signal while stopped blocks starting.
Affected models and serial ranges
3428 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
Can I keep running the engine with code 3428 active?
If the engine is already running when the secondary sensor signal is lost, performance is generally not affected because the ECM keeps using the primary sensor. However, you should get it diagnosed soon, because if the primary sensor signal is also lost, the ECM will shut the engine down, and if you shut the engine off, it will not restart until the fault is fixed.
Why won't my CAT engine restart after this fault code appeared?
The secondary speed/timing sensor signal is required for starting. If that signal is lost while the engine is stopped, the ECM will not allow the engine to restart, even though performance may not have been affected while it was running.
Can I swap the primary and secondary speed sensors to test which one is bad?
It depends on the engine. On some C13, C15, and C18 configurations the two sensors are interchangeable components and can be swapped to isolate a faulty sensor. On other configurations, the sensors are not interchangeable and swapping their positions is explicitly not recommended. Confirm your specific engine's sensor design before attempting a swap.
Does replacing the speed/timing sensor require a timing calibration?
No. For the configurations where the sensors are not interchangeable, no timing calibration is required after sensor replacement.
What other codes are related to 3428?
Some versions of this diagnostic require that code 0168-01 is not active and that no 0041 diagnostic codes are active for 3428 to set. If either of those codes is active, check and resolve them as part of your diagnosis.
What happens if both engine speed sensors fail at once?
Loss of signal from both the primary and secondary speed/timing sensors during operation causes the ECM to terminate fuel injection and shut the engine down. If both signals are lost during start-up, the engine will not start at all.
Is a faulty ECM a likely cause of code 3428?
It is listed as a possible cause on some versions of this diagnostic, but it should be considered only after ruling out more common issues like damaged wiring, connectors, the sensor itself, fuel pump timing, and the crankshaft or camshaft timing ring.