Engine ECM Power Supply Fault
The PACCAR-P1003 (PACCAR MX) diesel fault code means: Engine ECM Power Supply Fault. This is a serious severity code.
- Keep driving?
- No — stop driving
- DIY difficulty
- advanced
- Estimated cost
- $1,800-$4,500
Down with a PACCAR fault on the road?
Get connected with a verified mobile diesel mechanic near you. Verified diesel & reefer techs, launching on the freight corridor.
Find a mobile mechanic →A $30 car code reader can't do diesel. The HD7000 reads full-system codes and does parked DPF regen, idle/speed-limit, and service resets from the cab — on everything from a 6.7 Cummins/Power Stroke/Duramax pickup to Class-8 trucks (Detroit, Paccar, CAT, Volvo, Mack, International).
Full-system 6/9/16-pin diesel scan tool for Cummins, Paccar, CAT, Detroit and more — plug-and-play, no subscription. A cheaper way to read heavy-duty codes a basic OBD2 scanner skips entirely.
Affiliate links — we earn a commission at no extra cost to you.
Common Symptoms
- Check Engine Light illuminated
- Possible no-start or stalling
- Scan tool communication loss
- Engine derate or limp mode
Probable Causes (Ranked by Likelihood)
- ECM internal hardware fault Likely
- Software corruption requiring reflash Likely
- Power or ground circuit issue Possible
- Low battery voltage during key-on Possible
Frequently Asked Questions
What does PACCAR MX code P1003 mean?
PACCAR MX code P1003 (Engine ECM Power Supply Fault) 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 engine control system that should be diagnosed with DAVIE4 or PACCAR ESA.
Can I drive a Kenworth or Peterbilt with PACCAR P1003?
No — this fault typically triggers engine derate or forced shutdown countdown. Continuing to operate risks further damage or a stranded truck.
How much does it cost to fix PACCAR MX P1003?
Typical repair runs $1,800-$4,500. 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.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
Connect DAVIE4 or PACCAR ESA and confirm P1003 is active with freeze frame data.
Measure ECM supply voltage at pin — must be battery voltage key-on and stable during cranking.
Inspect ECM grounds at frame rail for clean, corrosion-free connections.
Check for PACCAR calibration updates and reflash if available.
If fault persists after reflash and wiring checks, ECM replacement with DAVIE4 programming is required.
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
- SAE J1939-73Application Layer: Diagnostics (defines the SPN/FMI fault-identifier framework)
P1003 on Other Platforms
The same code ID appears across other engines, vehicles, and equipment. Diagnostic flow varies by platform — see the matching breakdown:
Commonly Affected Vehicles
- Kenworth T680 with PACCAR MX-13
- Kenworth T880 with PACCAR MX-13
- Kenworth W990 with PACCAR MX-13
- Peterbilt 579 with PACCAR MX-13
- Peterbilt 389 with PACCAR MX-13
- Peterbilt 567 with PACCAR MX-13
- Kenworth T440 with PACCAR MX-11
- Kenworth T470 with PACCAR MX-11
- Peterbilt 520 with PACCAR MX-11
Explore More
Was this helpful?
Send this to whoever is fixing the truck — your tech, or the person asking what the fault means.