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1992 DeVille Intermittent Service Engine/Service Vehicle Check Engine Light

17482 Views 15 Replies 4 Participants Last post by  dennis93coupe
I have an intermittent 'Service Engine/Service Vehicle' light problem with my 1992 DeVille 4.9. About every 100 miles, the 'Service Engine Soon' light comes on, and then the 'Service Vehicle Soon' light also comes on. These lights will stay on for a few moments, then one or the other will go off, and they take turns coming on and off - sometimes both are on and sometimes only one is on. After a few miles, they both go out and everything is fine for another 100 miles or so and the phenomena repeats itself. We've used the OBD to check the the vehicle, but it shows no recorded codes. The vehicle has no obvious performance issues when the lights do this -- everything seems to be running just fine. The only other clue I have is that when this occurs, the 'Fuel Data Center' goes to 'zero' - i.e, the instant fuel economy reading reads zero, the gallons used works but doesn't accumulate more fuel used, etc. The fuel in tank seems to keep working fine.

Anyone have and ideas as to what this might be?
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Check the codes... even when the light goes back out it stored what code(s) made it come on in the first place.

with the key on press and hold the OFF and WARMER buttons and the same time and it will start to show the codes in the fuel data center. write them down and post back.

directions here:
Thanks. Did know know the system could report out with out a meter. Codes read were 'E47' and 'F32'.
I think ranger is onto something, especially since it seems to be intermittent.

info on E47: "This diagnostic test monitors the BCM to PCM/ECM serial data for a problem. Code E47 indicates that the PCM/ECM has lost BCM data. PCM/ECM diagnostics cannot be accessed when code E47 is set because the UART serial data communications between PCM/ECM and BCM are not working. To diagnose code E47 use BCM code chart F32.

NOTE: A faulty ignition switch can cause a false code E47 to be set. This will be caused by the switch powering the PCM/ECM before it powers the BCM. Code E47 and F32 can be stored together."

infor on F32:

"Code F32 is set by the BCM if a problem is detected transferring data back and forth to the PCM/ECM. If a hard code F32 is displayed upon entering diagnostics, one of the following conditions exist:

1. PCM/ECM to BCM data malfunction (CKT 526). If the BCM fails to receive data from the PCM/ECM, pin C9, over CKT 526, code F32 will be set immediately and the BCM will stop sending data to the PCM/ECM over CKT 491. When the PCM/ECM stops receiving data over CKT 491 it will set a code E47 in its memory, however, this code cannot be displayed since it would have to be sent over CKT 526 to the BCM. The loss of data to the BCM will result in a faulty instantaneous fuel economy reading of 0 mpg at all times.
2. BCM to PCM/ECM data malfunction (CKT 491). If the PCM/ECM, pin C11, fails to receive data from the BCM over CKT 491, code E47 will be set immediately by the PCM/ECM, however, data will continue to be sent to the BCM over CKT 526. Since the BCM continues to receive data, code F32 is not set immediately and instantaneous fuel economy reading will remain accurate. Upon entering diagnostics, the BCM will attempt to request diagnostic data from the PCM/ECM but cannot due to the malfunction in CKT 491. If diagnostic data is not received shortly after diagnostics is entered, the BCM will set F32 and will be unable to display the E47 stored in PCM/ECM memory.
3. PCM/ECM CALPAK malfunction. If the PCM/ECM fails to receive data from the PCM/ECM CALPAK, the PCM/ECM will stop sending data over CKT 526 and code F32 will be set immediately. If the hard code F32 is displayed, first check to see if the PCM/ECM can illuminate its service telltales during crank. If not, the PCM/ECM is not operating properly and should be diagnosed using the Self-Diagnostic System check. If the telltales work properly, observe the instantaneous fuel economy while the vehicle is moving. A malfunction in CKT 526 will result in constant reading of 0 mpg. If the reading varies normally, the cause of the code F32 is a malfunction in CKT 491. If no circuit problem can be found, one of the two modules is unable to process the data and should be replaced."


The following conditions will result in Intermittent BCM-ECM data codes F32 and/or E47.

1. Momentary open or short in CKT 526 restilts in both F32 and E47.
2. Momentary open or short in CKT 491 results in E47 only.
3. Momentary loss of ignition (CKT 50), battery (CKT 840) or ground (CKT 751-A) to BCM results in E47 and intermittent display panel operation.
4. Momentary loss of ignition (CKT 439) to PCM/ECM in F32, and intermittent engine.
5. Momentary loss of battery (CKT 480) or ground (CKT 450) to PCM/ECM results in F32, E52 and intermittent engine operation.
6. Momentary BCM PROM problem results in E47, F51, and intermittent display of "151" on CCP."
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I will be interested to hear what you find the problem is. I am having the same problems, short of pulling the dash apart I think I am looking to find another BCM. I need to wait awhile for the bank account to grow and recover from last month spending on repairs to get it running after being parked for 6 years.
I haven't had a change to check out the connections. This is stupid, but can anyone tell me where the ECM, PCM and BCM are physically located on the car? My first approach is to make sure all of the connections and grounds are good. dennis93coupe - I'll keep you posted.

All of those modules are behind the dash. Get yourself a copy of a genuine Cadillac Service manual for your model and year. Lots of them on ebay. It will save you a lot of money in the long run if you keep that car.
dennis if you have the FSM you can look up the location of the circuit (CKT) numbers and can check them... Also double check your FSM description of the codes. I pulled this info from alldata about my 1990 deville which i believe is the same or similar.
under "notes on intermittents" I would focus on #1 and #3 as those best describe your problem.

I'm searching through wiring diagrams trying to find the related circuits.
Ok here we go. again this is for a 90 deville I ASSUME its the same. And experts please speak up if im wrong, I dont want to send anyone on a wild goose chase. just trying to help out.

and before digging around under the dash always disconnect the negative cable on the battery.

Ok, we are going to find the CKT 526. It is on the lower left where it says "serial data (in)" and then has a C10 in a box and then the 526 brown wire. C10 is the connector number.

The BCM has 2 connectors on it. Im not sure how to tell them apart except im pretty sure they have the same letters and numbers as the pic below. On the second connector (c/d) your looking for c10 which is on the C column in the 10th row. it is called "PCM-BCM data" which is a brn (brown) wire.:

here is the location of the body control module (BCM) its on the passenger side under the dash and can be accessed when you remove the bottom cover of the dash:

The wire is possibly having an intermittent problem either grounding out or simply not making a connection at times.

grounding out could possibly be a nick in the wire and then having the bare spot touch something metal. Or, which is more likely imo, there is corrosion of some kinds on the connector pin. Not to sure. never has this problem b4. Maybe someone else can chime in about about to fix the prob.......

Just saw one of the CKT was a ground (751-A)... I will get a pic for the later and would probably be the first thing i would check
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No there are a few things different in the diagram. They don't show the EEC on the same page as BCM. OP has a 92, the manual for his is covered in the 92-93 DEVILLE/FLEETWOOD/SIXTY SPECIAL. After having the harness moved out of the way on mine when I resealed the valve covers, I need to go back and look at that as the main connectors are on that side of the body. So much to inspect looking for one of those problems. If the BCM failed, I suppose you also need to find out why as there might be a short or poor ground.
thanks dennis, my diagrams are probably of not much use then.
thanks dennis, my diagrams are probably of not much use then.
I wouldm't say that, they have left out or changed few things in the diagrams from what I can see. On page 8A-201-5 Figure E shows the PCM. I appears there are 3 connectors under the PCM that plug in. There are identifying numbers pointing to the harness S218, S246, and S285. It is located behind the RH side of the instrument Panel.I can't ell by looking at the diagram where it is in relation to other components. I would say for sure it is near the top of the dash with the connectors on the bottom side. I will say this from what I have read, they heavily emphasize on disconnecting the air bag to prevent it from deploy. You have a diagnostic energy reserve module that keeps power going to the air bag system. The wrong move and KABOOM!! If you are sitting in the passenger seat, the BCM is on top of heater A/C in the body under the dash. If you take the glovebox out, screws and there are the switches for the trunk release fuel door and connections fro the glove box light. You can see the relay center to the RH side, the BCM is to the left. If you have never been in the dash of these cars, I couldn't see doing it without the book.
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I couldn't see doing it without the book.
+1 alldata is ok, just hard to navigate. one of these days im gonna break down and buy the FSM.

and I had to go under the dash to replace the brake peddle switch and to get to some bolts to replace the evaporator. Trick is to get used to standing on top of you head (literally) and then diving into the sea of wiring, ducting, and modules.
+1 alldata is ok, just hard to navigate. one of these days im gonna break down and buy the FSM.

and I had to go under the dash to replace the brake peddle switch and to get to some bolts to replace the evaporator. Trick is to get used to standing on top of you head (literally) and then diving into the sea of wiring, ducting, and modules.
The FSM does help, probably more than Alldata? Anyway, I went back to the manual with a cleared mind. Sometimes it gets a bit boggling when you have all the pages to thumb through trying to find where this and that go. Just to get a better idea of where the components are, I thought I'd try to remove some connections and do some cleaning without pulling off the dash. I should take some pics and put them up on my hosting site. I am going to start from the beginning by what you are going to need to do just to see what you are looking for. Start by removing the cover under the dash all across from left to right, that way if you drop something, it will go to the floor and lett a little more light in. Next remove the glovebox, screws are all inside, be careful with the wires. Mark the wires or make a note how they connect to light and switches. They all have different connections so that should be easy. The drawings don't show all of the components together on the same page just the highlighed component with a herness and arrow to identify. When you are sitting in the passenger seat, you can see the RH fuse , relay center. I would say the PCM is just left of it closer to the firewall? The PCM has 3 connectors at the bottom of it, location page 8A-201-5. It is more of a vertical position. The BCM is behind the glove box, (above the heater A/C box, look for the levers on the the top of the box), look for 2 connectors, FSM page 8A-201-14A. Some of the drawings are pretty decent, some are real crappy. A full page drawing would have been nice. I don't know how hard it is to get the connectors off to clean, but it is worth looking at. Now that I think about having been in there, I think my PCM is loose whatever secures it to the body. I wasn't sure what module it was and had to button things up that night.
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