Low rail pressure is one of the most common cause of a limp mode in the 2001 – 2010 6.6 Duramax. DTC codes P0087, P0093 or P1093 may set due to low rail pressure.
Low rail pressure could be caused by a restricted fuel filter, air in the fuel, a bad pressure relief valve, excessive return fuel from the injectors or a worn CP3 pump. The least likely cause would be a fuel rail pressure sensor.
Fuel Supply and Fuel Filter
Check the fuel supply side first. Connect a gauge to the test port and check for excessive restriction. The “Filter Life Indicator” may falsely set if the rail pressure is too low. We often see this set within 500 to 2000 miles of installing a new filter. Vigorously shake the fuel filter into a clean container and look for contamination. If the filter is not restricted, or severely contaminated, then you likely have low rail pressure, but it may not be low enough to set a DTC. Or the filter life indicator may set with a low rail pressure code, leading you to incorrectly assume the filter is the cause.
For more information on checking the fuel supply and fuel filter, see our diagnostics information. 2001 – 2007 or 2007.5 – 2010
Rail Pressure Relief Valve
The pressure relief valve, or limit valve, if bad, will usually leak at higher rail pressures. The relief valve is in the system to prevent excessive rail pressure. Excess rail pressure could cause an injector to fail and dump the rail pressure into one cylinder, which could cause a hydro lock and engine damage.
Connect a clear line to the relief valve return, ramp up rail pressure and watch for a leak. If there is any fuel leaking from the relief valve, then it will need to be replaced.
Even if you replaced it with a block off plug, you should still check for a leak. We have seen several block off plugs leaking into the return, because they did not seat correctly into the rail.
Buy Duramax Rail Pressure Relief Valve
High Pressure CP3 Injection Pump
On vehicles with more than 200,000 miles on the high-pressure pump, we commonly see the CP3 pump cause low rail pressure. It fails to maintain enough rail pressure when the vehicle is pulling a load up a hill, and your Duramax may go into a limp mode. If the actual rail pressure is between 2176 psi or 2900 psi (depending on model year) below desired pressure, this would cause a P0087 or P0093 or P1093 code to set.
Depending on year of vehicle: P0087 will also set if the rail pressure drops below 3263 psi. P1093 will set if the difference between commanded rail pressure and actual rail pressure is more than 2900 psi.
Worn CP3 pumps that are not producing enough rail pressure under load usually do not cause hard starting. Buy Duramax CP3 Pump
Injectors
Excessive return fuel from the injectors can cause low rail pressure. If the injectors are worn enough to cause excessive return and low rail pressure, they will often cause a hard start. Perform the “Enhanced Injector Return Flow Test” to verify excessive return. Buy LB7 Injectors – Buy LLY Injectors – Buy LBZ Injectors – Buy LMM Injectors
Information is great. Very detailed with clear guidance to thoroughly help explore possibilities of issues
I hope you now know how to solve this issue with your Duramax.
Thanks
Would a turbo boost pressure low cause a 6.6 duramax diesel on a 08 chevy silverado 2500 to reduce power.
Hello Michael,
Most turbo low boost codes, such as P0299, will result in reduced power mode. Air intake, intake piping, boost leaks, MAF out of range, EGR issues or the turbo can cause this code. You would need to follow the diagnostics for the specific code that is setting.
Mark
My 06” duramax has less than 60,000 miles on it, issue started with excessive cranking, but after I learned about priming the pump it’s not had a hard start. I’ve replaced fuel filters & done periodic maintenance, now about 1-2 times a week it’ll go into a limp mode, the problem happens sometimes b-4 I go somewhere & also after she’s run fine! This problem will correct itself if I pull over & shut it down & fast turn my key?? So I thought it was mapping or electronic! As I said no issues starting it, & these events come & go within minutes after pumping the key, it’s not a consistent problem but a very aggravating problem, I’ve read the article above but if anyone has a more direct diagnosis after reading my post please let me know if there’s a direct link to a direct issue I’ve stated! Thanks
Hello Christopher,
The first thing to check is what codes are setting. When you cycle the key, it will reset some codes until it happens again. Once you know what code(s) set, then you can perform the diagnostics related to that code.
Thanks, Mark
Hi Mark. I appreciate your informative article. I have a ’04 2500HD with about 126K on it. I’m the third owner and I’ve had it about two years. It’s run great until now. I came a stop at an intersection the yesterday morning, and when I pulled out into traffic I suddenly had no power. It seemed the power dropped more as I pressed the accelerator further, then the power slowly returned as I let off the pedal. It happened again twice on that same drive, though less severely, and both times while ascending hills. It hasn’t been driven since. I picked up a code reader this morning and checked the OBD2. It threw codes of P1093, U0106, & P0198. I’m 100 miles away from home (in McMinnville) and must drive back home (Florence) tomorrow for work. Any suggestions would help relieve my state of panic. I think…
Hello Tim,
It does sound like the pressure relief valve is loosing rail pressure. Another possibility would be the cascade overflow valve however, I would check for return off the relief valve, or replace it. I assume you can not increase rail with your scan tool to verify leakage at higher pressures.
Give us a call when we open at 7:30, if you need to.
Mark
Hey Mark, I have a 2004 GMC 2500 HD Duramax. It has about 260k miles on it. I am having some trouble with my truck. When I first get in my truck and drive it, it drives fine until it gets warmed up. When it gets warmed up, as I am going down the road, all of a sudden it will start acting crazy. My engine will start making a bad noise and my truck will start jerking from it accelerating on its own. My RPMs will jump up without me even pressing the peddle. My fuel pressure will also fluctuate from 0 psi to 10,000 when it does act up. I have tried switching out my injector clips and it hasn’t helped. Please help. Thank you!
Hello Dakota,
Do you have any codes, not just a check engine light, but codes stored in the ECM? Cam or Crank sensors can cause the rpm to fluctuate erratically. We have also seen instances of the tone wheel coming loose. If you have a crank sensor code, you may need to look through the crank sensor hole and verify the tone ring is not wobbling. You may need to monitor, with a scan tool, the actual versus desired rail pressure while driving.
Give us a call after you have checked these possible issues
Mark
hey I have a 2006 LBZ with 295K on it and i just changed the fuel filter about a month ago (800-2000 miles is per month) i was pulling my landscape trailer up hill no problems and as soon as i crest over the hill CEL comes on, limp mode comes on and i pulled over plugged in my code reader and got a p0087 code. same code for the fuel filter that i replaced. i called a buddy who was a gm tech said to clear the code to get me home. got home and the CEL is back on. I have some thought to think it’s the relief valve, but its not leaking, other is the pressure sensor by the filter, I’m kinda lost could use some advice thanks!! also don’t have a lift pump don’t know if that helps or not.
Eli,
If the pressure relief valve is not leaking, and the high pressure pump is original, it is most likely the pump causing the issue. Excessive injector return can also cause low rail pressure, and you can check that here https://oregonfuelinjection.com/services-repair/diesel-diagnostics-repair/chevy-gmc-diesel-diagnostics/#01-injectors However, we see a lot of pump issues over 250k miles – see notes here https://oregonfuelinjection.com/services-repair/diesel-diagnostics-repair/chevy-gmc-diesel-diagnostics/#01-high-pressure-cp3-pump
Pump and install kit are here https://oregonfuelinjection.com/shop/chevy-gmc-duramax/2006-2007-6-6-l-lbz-duramax/cp3-fuel-injection-pump-6-6-lbz-lmm-06-10-duramax/ They do last longer with a FASS pump feeding them.
I have a 06lbz with 230k just went on a 50 minute drive, 50 minutes there and back and it went in fuel limp thought it wasn’t anything to worry about but it kept happening I just replaced my filters with cat filters one week ago
Hi Kaden,
What codes do you have setting? https://oregonfuelinjection.com/services-repair/diesel-diagnostics-repair/chevy-gmc-diesel-diagnostics/#01-dtc-codes
Did you check the pressure relief valve for leakage?
Do you have a way to monitor rail pressure? https://oregonfuelinjection.com/diy-repairs-and-obd2-diagnostic-phone-apps/
The most likely cause would be the pressure relief valve, then the CP3, then injectors. Follow the troubleshooting information above to try to pinpoint the cause.
Mark
2011 silverado 3500hd duramax dully kinda shuts off and on and it happens more the faster I go and it start after 5 to 10 mins of driving it the gauges shut off and go back on and the truck looses power took it to a service electrician checked everything but can’t find the problem just tells me it’s one of the 7 computers but his computer scanner doesn’t know what computer it is if anyone had has this problem and fix it plz help the truck has over 300000
Hello Ernesto,
The gauge cluster dropping out should not cause a loss of power or dying, unless one of the modules is knocking out the 5 volt reference of the CAN Bus. If it was the ECM, or related engine sensors, that should not cause the gauge cluster to drop out. If there are no codes, and it is random, it may be hard to pin down. If it acts up just idling, then you may be able to disconnect some of the modules or sensors, or do wiggle tests. We have not run across this particular problem before. Good luck.
Mark
2011 Duramax deleted goes into “Reduced Engine Power” mostly when I let off. The turbo has been changed and dos not feel strong at all, neither did the previous one. It is kind of gutless even without the LIMP mode kicking in. The turbo was someone else’s idea of the problem fix. It has had the vane sensor replaced as well. What is best diagnostic path with no codes?
Hello Daniel,
Sounds like a rail pressure issue. A lot of delete tuning throws a “blanket” over a lot of codes, not allowing them to set. The only way to find the problem is to actively monitor the PIDS or parameters and make certain they are in the proper range. You could start by checking rail pressure actual versus desired to see if it is low.
Mark
2008 Chev Silverado 2500HD 6.6L duramax turbo diesel LBZ
Which when stopped at a light with foot on brake and in drive, it wants to power up and go and you need to push brake with both feet to hold it back….what causes this?
It does not do this when putting in neutral. It is in Limp Mode. What would be the root cause of this problem? Transmission Control Module? Brake pedal position sensor?
Gas pedal position for throttle control?
You would need to start your diagnostics with…what are the codes? Then look through the diagnostic trouble tree to determine if any of the codes could be causing the issue. It could be the torque convertor trying to lockup however, that is not a common issue with the Duramax. It could be the speed sensor registering a false rpm and trying to keep from stalling.
Mark
My 05 LLy will goin into limp mode when I start it I can’t move but sometimes I will start it and it will be good and will work absolutely perfect until I shut it off and go out to start it again and it will be in limp mode any ideas on what that might be ?
Hello Elijah,
You will need to scan for codes. A typical limp mode is reduced power, which would occur on a hard pull or hard acceleration. If the truck is not moving after start up, I would think it is something transmission related, scanning for codes will tell you would is going on.
I appreciate your discussion, but my issue is a little different. 09 Duramax pulling a 12000 lb 5th wheel. No issues at all starting or driving without the RV. Truck will go into limp mode while pulling a load and the Change Filter warning and P0087 show. I change the fuel filter often with OEM parts, but a clean filter doesn’t seem to fix the issue. Usually happens with the fuel under half full, warm weather, pulling the RV usually on uphill grade. Never happens any other time. I have had the truck in dozens of times, no one can help. I can never repeat the problem for a mechanic to see. It happens at random times as mentioned above. Truck is well maintained with 130,000 miles. I have been using BG DFC+ fuel additive and that seems to help a little, but the problem exists. At my wits end, would appreciate your thoughts.
Hello Greg, your issue is a little different, but the same diagnostic approach applies. In some cases the “Filter Life Indicator” will be triggered prematurely, sometimes within 1000–5000 miles after changing the fuel filter. If this problem occurs even though the fuel filter is not restricted, it can be caused by excessive leakage on the high pressure side of the fuel system or other supply side issues. Verify there is no air in the supply system and restriction is not excessive under all load conditions. If these things check ok, diagnose the high pressure side as if there is low rail pressure codes. It seems that fuel flow is calculated in the ECM and is used to calculate fuel filter life. Or if rail pressure is below desired, even if the fuel pressure regulator actuation is high, the ECM assumes it can’t get enough fuel and the filter must be restricted. If the high pressure limit valve is bad as in the discussion, the fuel leaking by is calculated as return fuel. When there is too much fuel being returned from the injectors, it is calculated as return fuel. Here is a link to our Duramax diagnostics on our website: https://oregonfuelinjection.com/services-repair/diesel-diagnostics-repair/chevy-gmc-diesel-diagnostics/#07.5 Hope this helps, Scott