AUXILIARY FUEL PRESSURE - SPN 1868
The auxiliary fuel pressure is outside the normal range.
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What it means (plain English)
The computer measures the fuel pressure in the auxiliary system, and if it sees too low or too high a pressure, it triggers this code.
What the computer is actually seeing
The ECM expects the auxiliary fuel pressure to be between 4 and 6 psi when the engine is running. If it reads below 4 psi or above 6 psi for more than 10 seconds, it sets a fault.
What a healthy reading looks like
Expected auxiliary fuel pressure: 4-6 psi
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Verify the fuel level in the auxiliary tank. Is it sufficient to operate? If not, fill the tank and check if the code clears.
- 22. Check the wiring and connectors leading to the fuel pressure sensor. Are there any signs of damage or corrosion? Repair as needed and retest.
- 33. Test the fuel pressure using a gauge at the auxiliary fuel pressure sensor. Is it within 4-6 psi? If not, investigate the fuel pump and filter.
- 44. If the fuel pressure is correct, replace the fuel pressure sensor and clear the codes. Retest functionality.
Common causes
- Low fuel in the auxiliary tank
- Faulty fuel pump
- Clogged fuel filter
- Wiring issue between the sensor and the ECM
- Faulty fuel pressure sensor
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's moderate, so while it may drive, it could cause fuel delivery issues over time; fix soon.
Will this code come back after clearing?
If the underlying issue isn't resolved, it likely will return.
What happens if I ignore this code?
Ignoring it could lead to fuel system problems, affecting performance and reliability.
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