Cadillac Owners Forum banner

1 - 20 of 82 Posts

·
Registered
1997 Polo Green Cadillac Seville STS
Joined
·
685 Posts
Discussion Starter #1
97 STS, As I'm driving , I get the SERVICE FUEL SYSTEM message on the DIC. With PCM 0124 code. Fuel pump relay. This happened once before and I replaced the Fuel Pump Relay with a NEW OEM unit from GM... Tonight, it did it again. Burned up the new relay.:eek: So I swap the AC relay to the Fuel Relay. Works ok for about 20 mins. Then the SERVICE FUEL SYSTEM message starts to come back, then goes away. Does this 3 times on the way home. :rant2::rant2:

What the heck is causing the Fuel Pump Relays to fail so quickly??
 

·
Registered
2001 ETC Sequoia
Joined
·
878 Posts
Are you sure the relays are "burned up?" That sounds very unlikely.

A bad relay will cause long cranking times. Does yours crank/start/run normally? You didn't mention.

The reason for the long crank time is that there is a secondary power path to the fuel pump. It is provided by the oil pressure switch after the engine has developed sufficient oil pressure. Your engine should start and run even if the fuel pump relay is in your pocket. A code would be set, of course.

I think the odds favor a loose wire connection somewhere unless the relays are actually "burned."

Regards,
Warren
 

·
Registered
1997 Polo Green Cadillac Seville STS
Joined
·
685 Posts
Discussion Starter #4 (Edited)
No, it's never been hard to start. But once the SERVICE FUEL SYSTEM MESSAGE displays, it quits and will not start unless I change the relay. .. Upon taking the old relay out, it is VERY HOT. it'll almost burn my fingers. Not sure if this heat is present on the relay because of it's location in the engine compartment, or it's heated to the degree it would fail?...

I have the 97 FSM so if I needto pull the electrical diagrams I can, I just wanted to check here first to see if anyone else here is having similar problems and already knows a fix.


Warren,

Looking at the diagram you provided for the '98 Seville, it appears to be quite different compared to 97, 98 indicates the relay's location is at the "Rear Junction Block", while the '96-'97's relay location is in the forward (engine) compartment drivers side junction block.
 

·
Registered
1997 Polo Green Cadillac Seville STS
Joined
·
685 Posts
Discussion Starter #5
UPDATE:

On a hunch I reinstalled the Fuel Pump Relay that quit working last night. Car starts up fine with no codes and no messages on the DIC!!!!!...

Engine was cold from sitting overnight. Within 5 min the FP relay was HOT to the touch. I pulled it with engine running. engine runs for 5 seconds then stops.

FP Relay contact 30 & 85 on one side of the relay were very hot to the touch. Relay case was also hot , but the other 2 contacts on the other side of the relay were cool. I don't think this is normal.
 

·
Registered
1997 Polo Green Cadillac Seville STS
Joined
·
685 Posts
Discussion Starter #6

·
Registered
2001 ETC Sequoia
Joined
·
878 Posts
UPDATE:
Engine was cold from sitting overnight. Within 5 min the FP relay was HOT to the touch. I pulled it with engine running. engine runs for 5 seconds then stops.
The engine should continue running with the relay removed as the fuel pump should be energized by the oil pressure switch contacts. It should also start (after extended cranking) with the relay removed.

Perhaps the relay is getting hot because the relay is carrying the full current load of the pump and not sharing the current load with the oil pressure switch? I dunno, but I'd sure look into it.

Regards,
Warren

P.S. I should have posted the drawing from my old '95 manual; it would have been closer to yours. Since you have the FSM it doesn't affect you, but it might have confused other readers. Brain fart, I guess. Apologies.
 

·
Registered
1997 Polo Green Cadillac Seville STS
Joined
·
685 Posts
Discussion Starter #8
Well guys, I drove the STS to work today and ..... Nothing happened.. So whatever the problem is , it's going to be a hard one to track down...

On another note, I've heard from alot of the forum members talking about the Fuel Pump and how it can run off the oil pressure switch...

I think that applies only to the 98-up Northstars and NOT the 92-97. I've looked over the FPump relay schematics in the 96-97 FSM. There is no mention of the oil pressure switch being tied onto the Fuel Pump operation CKT.
 

·
Registered
2001 ETC Sequoia
Joined
·
878 Posts
I think that applies only to the 98-up Northstars and NOT the 92-97. I've looked over the FPump relay schematics in the 96-97 FSM. There is no mention of the oil pressure switch being tied onto the Fuel Pump operation CKT.
Look again. More closely. :)

Dunno about the '92, but if it's a Northstar the fuel pump runs off of the oil pressure switch/pump relay! Bank it!

Regards,
Warren
 

·
Registered
1997 Polo Green Cadillac Seville STS
Joined
·
685 Posts
Discussion Starter #10
Look again. More closely. :)

Dunno about the '92, but if it's a Northstar the fuel pump runs off of the oil pressure switch/pump relay! Bank it!

Regards,
Warren
Alright, I will when I get home tonight... The diagram I was using in the FSM is the one listed under DTC PCM P0231 Which deals with the one the STS is displaying when the "Service Fuel System" message gets thrown up on the DIC
 

·
Registered
1996 Eldorado Sport Coupe, 2009 Black Navigator
Joined
·
5,032 Posts
Strange but I'm also having a similar problem (96ESC) only mine starts but after a while it will stall and not start, just cranks. I also get the DTC0231. I'm praying its not the fuel pump.:rant2: BTW Gearheaad43, does your fuel pump relay look like this or does it have four prons?
 

·
Registered
1997 Polo Green Cadillac Seville STS
Joined
·
685 Posts
Discussion Starter #12 (Edited)
Strange but I'm also having a similar problem (96ESC) only mine starts but after a while it will stall and not start, just cranks. I also get the DTC0231. I'm praying its not the fuel pump.:rant2: BTW Gearheaad43, does your fuel pump relay look like this or does it have four prons?


It is light gray and has 4 prongs... labeled 30, 86, 88, 87. Mine are brand new from a local GM dealer... Even the dealer had trouble identifying the right relay cause the "General" likes to change P/N's so often!!!!:rant2::rant2:aND btw AL, My STs does the SAME dammed thing after the relay goes.. It Cranks but WILL NOT start no matter what I do.... I pop a good "cool" relay in and she fires right up!!!!

To me all that shit can olny mean 3 things.... Either the PCM is screwed, the Oil Pressure switch has kicked the bucket, OR the dammed FP has just decided to quit and piss me off. ...However I would think that if the Oil Pressure switch is bad, then the oil light on the dash or a LOW OIL PRESSURE message would display on the DIC... I guess I need to find out how the OIL PRESSURE SWITCH is wired to the FP.......
 

·
Registered
1996 Eldorado Sport Coupe, 2009 Black Navigator
Joined
·
5,032 Posts
It is light gray and has 4 prongs... labeled 30, 86, 88, 87. Mine are brand new from a local GM dealer... Even the dealer had trouble identifying the right relay cause the "General" likes to change P/N's so often!!!!:rant2::rant2:
The fuel pump relay in our cars have four prons but if you look at the pictures from gmpartsdirect.com & rockauto.com 95,96,97 they both give the picture of the five pron fuel pump relay. I brough one from a AC Delco shop and thought he sold me the wrong relay until I did some research. So if thats the fuel pump relay where does it go?
 

·
Registered
1997 Polo Green Cadillac Seville STS
Joined
·
685 Posts
Discussion Starter #14
That is because they like to use generic pics of parts that may or may not reflect the appearance of the part you need. I for one would NEVER trust a picture source from these places or any parts place.

I'm assuming the '96-'02 Eldorados are similar to the '96-97 Sevilles... If that is true, then the Fuel Pump Relay will be located near the air cleaner, there is a compartment with a square lid on it. Flip it open, and on the backside of the lid it'll have the descriptions of the fuses and relays. There should be 2 relays together near the bottom. Lower one is the Fuel Pump Relay & the upper one is the A/C Relay. In emergencies, you can actually swap the A/C relay for the Fuel Pump Relay so you don't end up stranded
 

·
Registered
2000 Eldorado ESC
Joined
·
1,362 Posts
Here's a wiring diagram from a '98 Seville. It might be similar to yours.
Warren, check your 95 FSM, you can see where the oil pressure switch and fuel pump relay feed into the same circuit, 1B13 on the PCM.
The diagram you posted only shows the oil pressure switch giving a ground signal to the PCM, not involved with the fuel pump circuit.
That may be why his engine dies when he pulls the relay.

Maybe try pulling your fuel pump relay, and verify that Caddy still uses the oil pressure switch back-up.
 

·
Registered
1996 Eldorado Sport Coupe, 2009 Black Navigator
Joined
·
5,032 Posts
My car is a 96 and it also has the new relay. Carfax shows the car was purchased in 95 so its not a end of the year built 96. Anywho thanks for the clarification.:thumbsup:
 

·
Cadillac Technician
none
Joined
·
11,051 Posts
There are a few points to make here:

1. The relays do get hot to the touch, hotter than you might think, not necessarily as hot as yours seems to be but...
2. GM quit using the oil pressure switch as a backup for fuel pump operation a long time ago, mainly for safety reasons. Most modern cars don't combine these systems anymore. I forget what year they stopped doing it, but looking at the schematics will show whether the oil pressure switch is involved or not.
3. If the fuel pump was really overcurrenting it would blow the fuse up the line.

It sounds like the PCM's monitoring circuit might have a problem or you could have a loose terminal in the relay block.
Sometimes when they overheat like that it can cause the terminals to "open up", this would make the condition even worse, and it might set codes.
Look at all the terminals in the relay block, see if one is more "open" than the others. If that is the case I'd say you found the problem... fixing it... well that is another problem.
 

·
Registered
2000 Eldorado ESC
Joined
·
1,362 Posts
2. GM quit using the oil pressure switch as a backup for fuel pump operation a long time ago, mainly for safety reasons. Most modern cars don't combine these systems anymore. I forget what year they stopped doing it, but looking at the schematics will show whether the oil pressure switch is involved or not.
.
That's what I saw with the wiring diagram WarrenJ posted, (98 model year) no connection between the oil pressure switch and fuel pump circuit, must have been either 96 or 97 they stopped that. My 95 FSM shows the oil pressure back up still there.
 
1 - 20 of 82 Posts
Top