CAT Engine 17973 Fault Code: Fuel Rail Pressure Sensor : Voltage Above Normal
Also called Engine Injector Metering Rail #1 Pressure : Voltage Above Normal, Fuel Rail Pressure Sensor - Voltage Above Normal, Fuel Rail Pressure Sensor Voltage Above Normal, Fuel Rail Pressure Sensor voltage above normal
Fuel Rail Pressure Sensor : Voltage Above Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 17973 (SPN 157 / FMI 3) means the ECM sees fuel rail pressure sensor signal voltage above 4.7 VDC or 4.8 VDC for 0.6 seconds. The engine will derate and the electronic service tool will show "70000 kPa" for both desired and actual fuel rail pressure. Applies to C13, C15, C175, and C18 engines.
High severity. The engine will derate as soon as this code goes active, which limits power and can affect job productivity and safe operation under load. It is not an immediate shutdown risk but should be diagnosed promptly to restore full power and confirm actual rail pressure is being read correctly.
What does CAT Engine error code 17973 mean?
Code 17973 is a Caterpillar diagnostic trouble code, SPN 157 / FMI 3, that flags a fuel rail pressure sensor signal voltage reading that is too high to be valid. The ECM expects a certain voltage range from the sensor to calculate actual fuel rail pressure. When the signal climbs above 4.7 VDC or 4.8 VDC (depending on the specific software version) for 0.6 seconds, the ECM decides the reading is not trustworthy.
Because the ECM can no longer trust the rail pressure reading, it stops using the sensor value for fuel control and instead displays a fixed placeholder value of "70000 kPa" for both Desired Fuel Rail Pressure and Actual Fuel Rail Pressure on the electronic service tool. To protect the engine and injection system from running on bad pressure data, the ECM derates the engine, cutting available power until the fault is corrected.
This code will only go active if there are no active 5-volt supply codes (0262) and no active 0168 code (battery or system voltage issue). Those codes point to broader electrical supply problems that must be resolved first, since they can cause a fuel rail pressure sensor to read incorrectly without the sensor or its wiring actually being at fault.
What triggers a CAT Engine 17973 code?
The ECM sets this code when the fuel rail pressure sensor signal voltage exceeds 4.7 VDC to 4.8 VDC for 0.6 seconds, and only when no active 0262 (5-volt supply) codes and no active 0168 code are present.
Common causes of 17973
- Damaged connectors or wiring at the fuel rail pressure sensor, engine harness, or ECM connector
- Problem with the wiring harness, including an open circuit in the sensor signal wire between the ECM and sensor
- Open circuit in the common wire for the sensor
- Short circuit between the sensor harness connector and the ECM, or a short to a voltage source
- Loss of reference ground at the sensor circuit
- Sensor supply voltage out of normal range
- Faulty fuel rail pressure sensor
- Faulty ECM
- Intermittent fault in the wiring harness or connectors
How to troubleshoot CAT Engine 17973: first checks
- Inspect the fuel rail pressure sensor connector and the engine harness connector for corrosion, moisture, bent pins, or loose terminals
- Check the wiring harness between the ECM and the sensor for chafing, pinches, or damage, especially near the sensor supply and common wires
- Verify there are no active 0262 (5-volt supply) or 0168 codes first, since those must be cleared before 17973 will set and may point to the real root cause
- Check the 5 VDC sensor supply and reference ground circuits for proper voltage and continuity, since the sensor supply feeds all 5-volt sensors and a wiring problem there affects more than one circuit
- Test the sensor signal wire for an open circuit or a short to a voltage source between the ECM and the sensor
- If wiring and connectors check out, test or replace the fuel rail pressure sensor before suspecting the ECM
How the code clears
No separate clearing step is listed beyond correcting the wiring, connector, sensor, or ECM fault. Once the underlying issue is repaired and the signal voltage returns to a normal range, the code should stop being active and the derate should lift. Confirm with the electronic service tool that Desired and Actual Fuel Rail Pressure are reading normal values instead of "70000 kPa."
Affected models and serial ranges
17973 appears in our records across 4 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 |
| C175 | Serial range not listed in source records |
| C18 | Serial range not listed in source records |
Frequently asked questions
What does CAT code 17973 mean?
It means the ECM detected the fuel rail pressure sensor signal voltage above 4.7 VDC to 4.8 VDC for 0.6 seconds, which is higher than a valid reading should be. The ECM logs the code, derates the engine, and shows "70000 kPa" for both desired and actual fuel rail pressure on the service tool.
Why does the display show 70000 kPa for fuel rail pressure?
That is a fixed placeholder value the ECM displays once it decides the sensor signal is invalid. It does not reflect actual rail pressure, it simply tells you the ECM is no longer using the sensor's real reading.
Will this code cause a loss of power?
Yes. The engine will be derated as part of the ECM's response to this code, which limits available power until the issue is fixed.
Can this code set on its own or does it depend on other codes?
It depends on other codes not being active. Specifically, no 0262 codes for the 5-volt supply and no 0168 code can be active, since those point to broader supply voltage issues that need to be resolved first.
Is this likely a wiring problem or a bad sensor?
Both are possible causes. Damaged connectors, harness problems, open or shorted wiring, and loss of reference ground are all listed causes, along with a faulty sensor or, less commonly, a faulty ECM. Wiring and connectors should be checked first since they are the more common culprits.
Which engines does fault code 17973 affect?
This code applies to CAT C13, C15, C175, and C18 engines equipped with a fuel rail pressure sensor monitored by the ECM.
Is it safe to keep running the engine with this code active?
The engine will run in a derated state, so it is not an immediate emergency, but full power will not be available and the underlying fault should be diagnosed and repaired as soon as practical to restore normal performance.