DEF Pump Pressure Low
The PACCAR-P1507 (PACCAR MX) diesel fault code means: DEF Pump Pressure Low. This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- intermediate
- Estimated cost
- $600-$3,800
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Common Symptoms
- DEF warning lamp and derate countdown
- SCR system inducement active (speed limit, no-restart)
- Poor fuel economy
- White crystal deposits near DEF doser
- Excessive DEF consumption
Probable Causes (Ranked by Likelihood)
- Crystallized DEF at doser tip or pump head Likely
- Failed NOx sensor (common wear item) Likely
- DEF pump module motor or seals worn out Possible
- Contaminated DEF (diesel, water, or aged fluid) Possible
- Frozen DEF lines with failed heater Possible
Step-by-Step Diagnostic Procedure
Check DEF tank with refractometer — concentration should be 32.5% urea. Replace if out of spec.
Connect DAVIE4 and command DEF pump pressure build test. Should reach target pressure within seconds.
Inspect DEF doser for crystallization — remove, clean with warm distilled water, reinstall.
Scan both NOx sensors live — a stuck, drifting, or slow sensor is the most common SCR fault.
If SCR efficiency fault persists after sensors and doser are verified good, catalyst may be contaminated.
Frequently Asked Questions
What does PACCAR MX code P1507 mean?
PACCAR MX code P1507 (DEF Pump Pressure Low) is a serious-severity diagnostic trouble code set by the engine or aftertreatment control module on MX-11 and MX-13 engines in Kenworth and Peterbilt trucks. It indicates a fault in the SCR/DEF system that should be diagnosed with DAVIE4 or PACCAR ESA.
Can I drive a Kenworth or Peterbilt with PACCAR P1507?
Possibly — short distances may be OK, but ignoring the fault risks progressive damage, regen failure, or derate. Address promptly.
How much does it cost to fix PACCAR MX P1507?
Typical repair runs $600-$3,800. Sensor or wiring repairs are at the low end; injector, DEF pump, DPF, or EGR cooler jobs are at the high end. Dealer-level DAVIE4 software is often required for programming or calibration after parts replacement.
Sources
This page is built from documented references. Verify against your own service info before repair work.
P1507 on Other Platforms
The same code ID appears across other engines, vehicles, and equipment. Diagnostic flow varies by platform — see the matching breakdown: