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Cat Man
Cat Man, Caterpillar Engine Expert
Category: Heavy Equipment
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Experience:  23 Years Caterpillar Engine experience.
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Hi, have 2003 cat 3126 hep19701 in RV...crank..Was flashing code 55.

Resolved Question:

Hi, have 2003 cat 3126 HEP19701 in RV. Will crank but not start / fire. Was flashing code 55. Went to cat dealer, explained and he had me change regulator AS (fuel) at head (294-8620). Cat said this is first thing they would change if I brought in. Trying to avoid having towed at $600.00. Installed new fuel /water filter and air prior to installing regulator. Still will not start. Now showing code 49 since changing regulator today. Had fuel at hose to regulator prior to changing. Will fire with a little shot of stating fluid. Pressureized fuel tank also today. I probably cranked 12/15 times today and no luck with starting. Was running fine, always started easy. Moved in morning, ( 1 week ago) was sluggish starting that afternoon and has never started since then.
Thanks Tim
Submitted: 5 years ago.
Category: Heavy Equipment
Expert:  Cat Man replied 5 years ago.
Hi. Thanks for using JA! I will try and help you out.

I would like to measure the fuel pressure while cranking the engine if possible. Your engine needs at least 25 psi to crank. Even though you replaced the regulator, you could possibly have a bad transfer pump.

Please let me know if you have any more questions.
Customer: replied 5 years ago.
Thanks, XXXXX XXXXX check prussure right before regulator? Can I change the fuel pump if no pressure? is there any other in line screen filters. I have only one fuel filter, that is fuel / water seperator? I also forgot to tell you after changing regulator engine code went from 55 to 49. That code makes no sense.
Expert:  Cat Man replied 5 years ago.

You are welcome.


There should be a plug located on the secondary fuel filter housing that you can install a psi gauge into. The engine does not have any inline filter screens.


If the fuel pump is the problem on yur engine, you will need to remove the HEUI pump/fuel pump assembly together. On HEP engines, you cannot just remove the trnafer pump from the HEUI pump. It iwll cause damage to the HEUI pump. THe entire assmebly must be removed and then there is a special bolt that is needed to replace the transfer pump.


Code 49 is a fault with the intake air heater. Not sure why that would come on after replacing the regulator. However, code 49 cannot keep your engine from starting.

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