CAT Engine 5448 Fault Code: Engine Cooling Fan Speed signal abnormal
Also called Engine Cooling Fan Speed Sensor - Abnormal Frequency, Pulse Width, or Period, Engine Cooling Fan Speed Sensor : Abnormal Frequency, Pulse Width, or Period, Engine Cooling Fan Speed Sensor:Abnormal Frequency, Pulse Width, or Period, Engine Cooling Fan Speed Signal Abnormal
Engine Cooling Fan Speed signal abnormal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 5448 means the ECM sees the engine cooling fan speed signal outside its normal operating range, either too slow or too fast, while engine speed conditions say it should be reading normally. The ECM flags the fan speed data as invalid and falls back to running the fan control solenoid off the temperature strategy alone. Applies to C13, C15, C18, C27, and C32 engines.
Medium severity. This is not an immediate shutdown code, but losing valid fan speed feedback means the ECM can no longer confirm the cooling fan is actually responding to commands. Left unaddressed, this can lead to undetected overheating or a fan that runs continuously and wastes power, so it should be diagnosed within the shift, sooner if coolant temperatures start climbing.
What does CAT Engine error code 5448 mean?
CAT code 5448 fires when the ECM detects that the signal from the engine cooling fan speed sensor is out of its expected range: the fan speed reads below 38 rpm or above 2000 rpm for a sustained period while the engine itself is running in a speed range where the fan should be behaving normally. The ECM cannot tell if the fan is actually spinning correctly, so it marks the fan speed data as invalid.
The engine cooling fan speed sensor sends a pulse signal to the ECM once per fan revolution. It runs on an 8.0 ± 0.5 VDC supply from the ECM, and its output frequency scales with fan speed, ranging from 5 Hz to 180 Hz across a fan speed range of 50 rpm to 1800 rpm. The ECM uses this signal to confirm the fan is turning at the speed it commanded through the fan control solenoid.
When this code is active, the ECM stops trusting the fan speed signal and switches to running the fan control solenoid purely off the engine temperature strategy, without speed feedback. On some machines without the fan speed hardware installed, this code can also appear if the 'Engine Fan Control' parameter was mistakenly enabled.
What triggers a CAT Engine 5448 code?
The ECM sets this code when all of the following are true: fan speed is less than 38 rpm, or greater than 2000 rpm, for 1.9 seconds (one version of the logic lists 2 seconds); engine speed is between low idle and 2400 rpm for one minute; diagnostic codes for digital sensor supply short to battery (263-03) and short to ground (263-04) are not active; and the ECM has been powered for at least three seconds.
Common causes of 5448
- Damaged connectors or wiring at the fan speed sensor or ECM harness
- A general problem within the wiring harness itself, such as chafing or a loose connection
- A faulty fan speed sensor
- A faulty fan drive assembly
- A faulty fan control solenoid
- An intermittent electrical problem that comes and goes
- A faulty ECM, though this is the least common cause and should be the last thing checked
How to troubleshoot CAT Engine 5448: first checks
- Inspect the fan speed sensor connector and the ECM harness connectors for corrosion, moisture, bent pins, or loose terminals
- Check the wiring between the sensor and the ECM for chafing, pinches, or damage, especially anywhere it runs near the fan shroud or hot exhaust components
- Confirm the sensor supply voltage matches the expected 8.0 ± 0.5 VDC using a multimeter with the key on
- With the engine safely running and the fan accessible, verify the sensor output frequency changes appropriately with fan speed, checking it falls within the 5 Hz to 180 Hz range across the 50 rpm to 1800 rpm range
- Inspect the fan drive assembly for wear, damage, or anything that could cause erratic or out-of-range fan speed
- Check for related digital sensor supply codes (263-03 or 263-04) since these must be inactive for 5448 to set, and their presence points to a supply circuit issue instead
- Use Caterpillar Electronic Technician (ET) to view live fan speed data and confirm whether the signal is genuinely erratic or simply out of range
How the code clears
No separate clearing procedure is listed for this code. Once the underlying wiring, connector, sensor, fan drive, or solenoid issue is repaired and the ECM sees a valid fan speed signal within the normal range, the code should stop being active on its own. Confirm the fix using a display module or Caterpillar Electronic Technician (ET) to verify the fault no longer sets during operation.
Affected models and serial ranges
5448 appears in our records across 5 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 |
| C27 | Serial range not listed in source records |
| C32 | Serial range not listed in source records |
Frequently asked questions
What does CAT fault code 5448 mean?
It means the ECM is seeing an abnormal fan speed signal, either far too low or far too high, from the engine cooling fan speed sensor while other engine conditions say the reading should be normal. The ECM then treats the fan speed data as invalid.
Is it safe to keep running the engine with code 5448 active?
You can typically keep operating short term since the ECM falls back to running the fan solely off the temperature strategy, but you lose fan speed feedback. Watch your coolant temperature gauge closely and get the fault diagnosed within the shift since an undetected fan problem can lead to overheating.
What is the fan speed sensor supply voltage supposed to be?
The ECM supplies the sensor with 8.0 ± 0.5 VDC. If this voltage is out of range, check for related codes 263-03 (short to battery) or 263-04 (short to ground), since either of these being active will prevent 5448 from setting in the first place.
What fan speed range should the sensor read?
The sensor output frequency should vary between 5 Hz and 180 Hz as fan speed varies from 50 rpm to 1800 rpm. Code 5448 sets when the reading falls below 38 rpm or climbs above 2000 rpm for a sustained period.
What are the most common causes of this fault?
Damaged connectors or wiring, a general harness problem, a faulty fan speed sensor, a worn or damaged fan drive assembly, a faulty fan control solenoid, and intermittent electrical faults are all listed causes. A faulty ECM is possible but far less common.
Can this code appear on a machine that isn't equipped with a fan speed sensor?
Yes. If the machine lacks the hardware for this feature but the 'Engine Fan Control' parameter was changed to 'Enabled', the ECM can generate this code even though no sensor is physically present.
Do I need a scan tool to diagnose code 5448?
A scan tool such as Caterpillar Electronic Technician (ET) makes this much easier since it lets you view live fan speed data and confirm whether related digital sensor supply codes are active, but a multimeter check of sensor voltage and wiring can also narrow down the cause.