Low Pressure Fuel System Pressure Too High
What does DURAMAX-P008B mean?
The DURAMAX-P008B (Duramax) diesel fault code means: Low Pressure Fuel System Pressure Too High. This is a serious severity code.
Common Symptoms
- Extended cranking or no start
- Loss of power / 'Reduced Engine Power' message
- Limp mode
- Metal shavings in fuel filter (if CP4 failed)
- Strong fuel smell
Probable Causes (Ranked by Likelihood)
- Lift pump regulator stuck Very Likely
- Failed fuel pressure regulator / FCA valve Likely
- Plugged fuel filter (service interval every 15K) Possible
- Air in fuel system Less Likely
- Cracked high-pressure fuel line Less Likely
Step-by-Step Diagnostic Procedure
Pull the fuel filter and inspect for metal debris. Metal = entire fuel system contaminated, requires full replacement.
Check fuel rail pressure with scan tool at key-on and during crank. Should see ~5,000+ psi at crank on LML/L5P
Test the fuel pressure regulator before condemning the pump — cheaper to replace first
Inspect fuel tank pickup and lift pump output
If CP4 pump has failed, recommend a CP3 conversion kit to prevent repeat failure
Frequently Asked Questions
What is P008B on a Duramax?
Duramax code P008B (Low Pressure Fuel System Pressure Too High) is a serious-severity diagnostic trouble code triggered by the engine control module when it detects a problem in the associated system. The Bosch CP4.2 pump in LML and L5P Duramax engines is known for catastrophic self-destruction, contaminating the entire fuel system.
Is a Duramax P008B safe to drive?
NO. If the CP4 pump has failed, continuing to drive spreads metal through injectors, lines, and tank. Tow to the shop.
How much does it cost to fix P008B on a Duramax?
FPR $400-$800. Plugged filter $40-$100. Full CP4 failure $7,000-$12,000. CP3 conversion $4,500-$6,000.
P008B on Other Platforms
The same code ID appears across other engines, vehicles, and equipment. Diagnostic flow varies by platform — see the matching breakdown: