Fuel Delivery Pressure - Data Valid But Above Normal
What does CUMMINS-1257 mean?
The CUMMINS-1257 (Cummins) diesel fault code means: Fuel Delivery Pressure - Data Valid But Above Normal. This is a moderate severity code.
Common Symptoms
- Hard starting or extended cranking
- Power loss under load
- Rough idle and stalling
- Black smoke or white smoke at exhaust
- Poor fuel economy
Probable Causes (Ranked by Likelihood)
- Failed high-pressure fuel pump (CP3 or CP4) Likely
- Clogged fuel filters (primary or secondary) Very Likely
- Failed or stuck fuel rail pressure regulator Likely
- Leaking or stuck injector Possible
- Weak lift pump causing low supply pressure Possible
- Wiring or harness damage at injector or rail Less Likely
Step-by-Step Diagnostic Procedure
Connect INSITE, command injector cutout test, and observe RPM drop per cylinder to localize injector faults.
Verify fuel rail pressure on INSITE matches commanded pressure (within 10%) at idle and under load.
Inspect both fuel filters (primary/water separator and secondary) for restriction -- replace if overdue.
Check lift pump supply pressure at inlet to CP3/CP4 high-pressure pump (spec varies, typically 5-10 psi).
Inspect fuel return line flow per injector using a return-line test kit to spot a leaking injector.
Check fuel for water contamination and microbial growth -- drain water separator before starting.
If high-pressure pump is suspect, perform a pump low pressure test; replace pump and contaminated fuel if failed.
Frequently Asked Questions
What is Cummins fault code 1257?
Cummins fault code 1257 indicates: Fuel Delivery Pressure - Data Valid But Above Normal. It is a moderate-severity fault in the fuel delivery system.
Can I drive with Cummins fault code 1257?
Yes, short-term driving is typically safe with fault 1257, but the fault will illuminate the Check Engine Light and must be diagnosed soon. Monitor for power loss, unusual noises, or gauge changes and pull over if conditions worsen.
How much does it cost to fix Cummins fault 1257?
Repair cost is approximately $300-$1,200 including parts, labor, and any dealer programming required. DIY repairs (sensor replacement) fall at the low end; pump, aftertreatment, or ECM work falls at the high end and usually requires INSITE diagnostic software.