How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29534
Experience:  GM Grand Master Technician 2007. 14 years experience.
Type Your Chevy Question Here...
GM Tech (Cam) is online now
A new question is answered every 9 seconds

gmc: 2500 HD..that keeps coming on and the vehicle goes into Limp Mode

Customer Question

I have an 01 GMC Duramax (2500 HD) with the P0093 that keeps coming on and the vehicle goes into Limp Mode. I replaced the Fuel Pressure Regulator Sensor and that did not help. I am considering the Fuel Pressure Regulator and the CP3, but am having trouble finding out "book tome" for these repairs. Trying to find out if it would suit me best to do both, or would it be best to do the regulator first, and gamble that this is it. What is your experience with the regulator vice the CP3 for this problem. It has 169K and has had the injectors replaced.
Submitted: 6 years ago.
Category: Chevy
Expert:  Jettadan1 replied 6 years ago.

My Answer is based on clues, symptoms and info in your question. Please include everything. Thanks


Hello I am pulling up testing on your code now. I can find you some procedures.

Expert:  Jettadan1 replied 6 years ago.
Click here. Here is testing more to come.
Customer: replied 6 years ago.

Vehicle drives just fine when not under load. When I try to jump on it, or am pulling a load, the P0093 code comes up when the truck tries to down shift, then goes into limp mode. As long as I can keep it under 2000RPM, the truck will keep going. I was on flat road pulling a hay trailer at 65 MPH just fine. When I hit a hill, I had to slow down to keep it under 2000 RPM. When the trailer was empty, I continued to get the same thing.

Performed the diagnostics based on fuel pressure in and out using the troubleshooting guidance online and it came up with the fuel pressure regulator sensor. I replaced that and wound up pulling a loaded car trailer at 70 mph on a flat road, but had the same problems empty and full as I did prior to the replacement.

Everything I see online points to the CP3 or the Regulator. The injectors were replaced at about 130K and I now have 169K on it. Trying to fix without replacing everything in a costly shotgun approach. If it looks like it will get into the thousands, then I may as well sell this one and get a newer one. Trying to figure out what to try, how to try it and what book time would be if I had someone do it. I have heared that the regulator can be replaced without removing the CP3 but do not know how extensive the work is. If it isn't the regulator, how much rework is involved if I replace the CP3.

Expert:  GM Tech (Cam) replied 6 years ago.

Hi, I'm Cam. May I ask your first name? I see Dan is offline.
I am working to get you a fast accurate answer. About your vehicle, there is a simple test to do to determine if the injectors are bad again or not.

Find the 2 fuel lines on the rear drivers side valve cover. Take the smaller one off and attach your hose to the metal pipe coming from the engine. Put the other end into the container and run the engine to fill that line. Then shut it off and remove the IGN 1 relay from beside the starter relay. empty out the container and keep the line full. Crank the engine for 15 seconds fully and measure the amount of fuel that comes out of that line. More than 40cc means the injectors have failed.


The pump and regulator often don't cause this so lets do this test first.