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Edward, Service Technician
Category: Cadillac
Satisfied Customers: 2745
Experience:  20 + years experience on various makes and models.
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Yesterday I took my 08 Cadillac CTS in to have the plugs &

Customer Question

Yesterday I took my 08 Cadillac CTS in to have the plugs & air filter changed. However when I picked it up today, I began having a reduced engine power light on the dash. Subsequently I can't go over 20 mph. The fuel pump was replaced less than a year ago due to a crack in the pump housing...Is your best guess the fuel filter?
JA: Have you checked the fuses? The dashboard bulbs?
Customer: Don't think fuses or bulbs would cause this problem.....Which fuse would you have me check?
JA: What year is your CTS?
Customer: 2008
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: Had it down to a local mechanic but he's going to be out of town for the weekend so was hoping there was something I could do myself.....I'm pretty adept at fixing things if I know where to look.
JA: Anything else you think the mechanic should know?
Customer: Only that it was working fine prior to changing the plugs, oil and air filter.....I left the shop and drove about 5 miles and it sputtered, and the engine basically went to an idle.
Submitted: 2 months ago.
Category: Cadillac
Expert:  Edward replied 2 months ago.

Hello, Eddie here and I will do my best to help. Do you have a scanner by chance? that we can check codes to see why the "reduced power" message came up?

Customer: replied 2 months ago.
Before he left for a LONG weekend, my mechanic indicated that the code was calling out the fuel rail pressure.
Expert:  Edward replied 2 months ago.

Alright, did he recommend replacing the plugs and air filter due to regular maintenance? or did he say perhaps that replacing these components would take care of this fuel rail pressure sensor code?

Customer: replied 2 months ago.
Well a couple of weeks ago...I had a check engine light. At that point he recommended based upon the code that the #1 cylinder either needed a new plug or new coil. So we decided to replace the plugs which he indicated today they looked to be reaching their life expectancy. I drove it about 5 miles, accelerated to the highway on ramp and had the check engine light come on and then the engine reduced power light (which I never had before). I took it back and he worked on it the rest of the day but ran out of time. The last thing he told me is that he felt it was something in the fuel supply based upon the code he was getting. (fuel filter/fuel pump/fuel pressure sensor.) Thought maybe you could help confirm and tell me where the fuel filter and/or pressure sensor were located on the CTS.
Expert:  Edward replied 2 months ago.

Alright, I follow you, There are actually two pressure sensors as far as your 08 CTS goes, one is in the carbon canister and is called the fuel tank pressure sensor, and it throws a code if you had a leak in the fuel tank, (like leaving the gas cap off for example) The other pressure sensor is called the fuel pressure sensor, it actually screws into the fuel rail itself at the intake manifold, this sensors gives the ECM information on how much fuel pressure is in the fuel rail available to the injectors. And it could set off the reduced performance light and give you that limp mode the vehicle is currently in. I would need you to scan for codes with a scan tool to be sure however, The sensor itself sells for around 100$ online, here is the PDF for fuel pressure sensor replacement.

Expert:  Edward replied 2 months ago.

The fuel tank pressure sensor would not give that limp mode symptom, It would set a check engine light, but I am confident you would still have full power with that code, however the fuel pressure sensor in the fuel rail at the engine, if it goes bad, it would put it in limp mode.

Customer: replied 2 months ago.
Okay.....well I'll see if I can pick one up locally and give it a try. At least I can eliminate 'something'.......Never a good time for these things to happen, but this weekend is especially bad. Thanks for your response and I'll get back to you after I replace the one in the fuel rail. long as I have the rail sensor out, would it be a good idea to replace the fuel filter. If so.....can you tell me the part # and location?
Expert:  Edward replied 2 months ago.

Whats the approximate mileage on it?

Customer: replied 2 months ago.
Approximately 80K
Expert:  Edward replied 2 months ago.

I'm not showing an operation for a standard inline fuel filter on this 08. That is odd, I'm still researching it here. I will respond asap. thanks.

Expert:  Edward replied 2 months ago.

OK, Cadillac moved the fuel filter to the fuel tank itself as part of the fuel pump assembly on your 08 model. There is no standard inline fuel filter on this model, But if it is an 8/07 build date or higher, then I'm 95% sure you will not see one there.

Expert:  Edward replied 2 months ago.

I should say it used to be just in front of the rear passenger side tire on the frame rail, but if it's an 8/07 build date or higher, I'm 95% sure you will not see one there.

Expert:  Edward replied 2 months ago.

So I would not worry about the fuel filter at this time. And check the codes again with a code reader, and if you do see that pressure sensor code, then I would go ahead with that replacement.

Customer: replied 2 months ago.
Okay.....well thanks for looking. I'll start with the fuel pressure sensor. Think they have them locally......and HOPEFULLY it won't take me all day to replace it and try it out.
Expert:  Edward replied 2 months ago.

Absolutely, I would see if you could borrow your friends scanner, or see if a local auto parts store would let you borrow one, sometimes they will with their tool loan program. That way you could double check the codes, and clear them out, then run it and see what it set FIRST, as you want to go after the first code it sets first. Let me know if you have any further questions. Thank you.

Customer: replied 2 months ago.
Will do....think the local Oreilly's will run a scan for me and they also have the sensor in stock.
Expert:  Edward replied 2 months ago.

Yes, they should do that free of charge. Write the codes down, all of them in the order they appear, then erase them, and start the vehicle again and let it run until you see that message again, then scan for codes again, whatever it set first after clearing them out will be the primary code and most likely setting any other codes that may be stored in memory.