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1987 Cadillac Sedan Deville Temp Light comes on when AC on


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Goldcaddy87
Novice

Oct 23, 2017, 10:03 AM

Post #1 of 14 (423 views)
1987 Cadillac Sedan Deville Temp Light comes on when AC on Sign In

1988 Cadillac Sedan Deville Temp Light comes on when AC on. When I switch off it turns off the Tem Light. No delay immediately. Any thoughts?




(This post was edited by Goldcaddy87 on Oct 25, 2017, 4:16 PM)


Hammer Time
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Oct 23, 2017, 10:51 AM

Post #2 of 14 (404 views)
Re: 1988 Cadillac Sedan Deville Temp Light comes on when AC on Sign In

It appears this car has 2 different temp lights. One of them is "Coolant temp/Fan indicator" and the other one is "Stop engine Temp Indicator". I don't know how it works for sure but it appears one light is supposed to come on when the cooling fans are operated which would be any time the AC is on.



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Goldcaddy87
Novice

Oct 23, 2017, 11:07 AM

Post #3 of 14 (396 views)
Re: 1988 Cadillac Sedan Deville Temp Light comes on when AC on Sign In

Did'nt think these had an Electric Cooling Fan. Time to look under the shroudSmile


Discretesignals
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Oct 23, 2017, 11:13 AM

Post #4 of 14 (388 views)
Re: 1988 Cadillac Sedan Deville Temp Light comes on when AC on Sign In

On the climate control panel hold the off and warmer button at the same time with the ignition on. It will display current or history trouble codes stored in the ECM and the BCM.

Trouble codes starting with "E" are ECM code and "F" is BCM codes.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Oct 23, 2017, 11:14 AM)


Hammer Time
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Oct 23, 2017, 11:16 AM

Post #5 of 14 (382 views)
Re: 1988 Cadillac Sedan Deville Temp Light comes on when AC on Sign In


Quote
Did'nt think these had an Electric Cooling Fan. Time to look under the shroud


It's a FWD car with a transverse engine. It has to be electric.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Goldcaddy87
Novice

Oct 23, 2017, 11:59 AM

Post #6 of 14 (378 views)
Re: 1988 Cadillac Sedan Deville Temp Light comes on when AC on Sign In

Pressed "Off and Warmer" and got E38 E52, E55 F41 F55 nothing I could relate back to the AC.


Discretesignals
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Oct 23, 2017, 2:17 PM

Post #7 of 14 (357 views)
Re: 1988 Cadillac Sedan Deville Temp Light comes on when AC on Sign In

E38 is open in the MAT(manifold air temperature) sensor circuit
E52 is Long term memory has been reset. That happens if the battery is disconnected.
E55 is TPS misadjusted

F41 is a TSB

Quote
88cadillac11

Bulletin No. T-89-18
File in Group 8
Number 86
Corp. Ref. No. 818112
Date Sept. 1988
SUBJECT: COOLANT TEMP/FAN TELLTALE ON INTERMITTENTLY AND CODE F41 SET

MODELS AFFECTED: 1988 DE VILLES AND FLEETWOODS


Some 1988 DeVilles and Fleetwoods may turn the Coolant Temp/Fan telltale on intermittently and set BCM code F41. Code F41 was eliminated on 1988 DeVilles and Fleetwoods with the elimination of the cooling fan module. However, if the incorrect BCM PROM is installed in these vehicles, code F41 may set as a result.

To check for an incorrect BCM PROM, check BCM parameter P.3.1 BCM PROM I.D. The correct BCM PROM I.D. for 1988 DeVilles and Fleetwoods is 22 or 23. If the BCM PROM I.D. is less than 22 (i.e., 20 or 21), replace the BCM PROM with the proper one as listed in the parts catalog, Section 3.670.

For warranty purposes use Labor Operation N4801 at .4 hour for BCM PROM replacement.






Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


Goldcaddy87
Novice

Oct 23, 2017, 9:06 PM

Post #8 of 14 (323 views)
Re: 1988 Cadillac Sedan Deville Temp Light comes on when AC on Sign In

Wondering if the BCM is actually at fault or the low pressure switch on the ac acting out (sending bad reading)? This only flips the Tem Light on almost as fast as I turn the AC on or turn it off. Happens really quick both ways.


Discretesignals
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Oct 24, 2017, 9:29 AM

Post #9 of 14 (276 views)
Re: 1988 Cadillac Sedan Deville Temp Light comes on when AC on Sign In

According to the TSB that code shouldn't exist in the BCM. Maybe at one time the BCM was replaced with an older version? Has it always done this? Do the cooling fans operate when you have the ac turned on? Does the ac blow cold?





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Oct 24, 2017, 9:45 AM)


Goldcaddy87
Novice

Oct 25, 2017, 4:16 PM

Post #10 of 14 (193 views)
Re: 1988 Cadillac Sedan Deville Temp Light comes on when AC on Sign In

My mistake. Its a 1987 by the VIN. Today when I started her up the AC powered on and cycled cold. A minute later the Temp light upper right hand on the Dash came on. The radiator is not running hot at all after 30 minutes and again if I flip-off the AC the Temp light turns out. The AC however did stop blowing cold. That being said I thought Id replace the ac pressure sender on the low side. Both the electric radiator fans operate. They are original equipment. I thought about maybe replacing them after all they are 30 years old. This Caddy has 49,000 miles on it. Unsure


Hammer Time
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Oct 25, 2017, 5:00 PM

Post #11 of 14 (184 views)
Re: 1988 Cadillac Sedan Deville Temp Light comes on when AC on Sign In

The 87 still has 2 different red temp lights and I still think one of them comes on to indicate the external fan has come on.





~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Goldcaddy87
Novice

Oct 25, 2017, 5:49 PM

Post #12 of 14 (177 views)
Re: 1988 Cadillac Sedan Deville Temp Light comes on when AC on Sign In

The light that comes on is on the right side and is the "Coolant Temp/Fan Indicator". Im just perplexed that I saw the Temp Fan red light come on and it blew cool for about 3 minutes then shut down. Howver if I turn the Ac off the Temp Light immediately turns off (2 seconds). That tells me the AC operation or the Fan is driving this light.


Hammer Time
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Hammer Time profile image

Oct 25, 2017, 5:53 PM

Post #13 of 14 (173 views)
Re: 1988 Cadillac Sedan Deville Temp Light comes on when AC on Sign In


Quote
That tells me the AC operation or the Fan is driving this light.


Isn't that what I just tried to tell you?



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Discretesignals
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Oct 26, 2017, 6:06 AM

Post #14 of 14 (141 views)
Re: 1988 Cadillac Sedan Deville Temp Light comes on when AC on Sign In

If this is an 1987 Deville, then F41 code means there is a problem with the cooling fan circuit.



Quote
Code F41 is set by the BCM if it receives the improper cooling fans feedback voltage. The cooling fans control module is designed to change the feedback voltage on circuit 791 as follows:

- 6-10V if the fans have been turned off.
- 0V if the fans have been turned on.
- 6-10V if the fans have been turned on and an excessive current draw exists (stalled or shorted fan motors)
- 0V if both fan connectors are open.

The BCM will set Code F41 if either of the following conditions exist:

A. The BCM has commanded the fans off but the feedback voltage remains low. The BCM will keep Code F41 hard for the rest of the ignition cycle and continue providing a normal control signal to the cooling fans control module. The BCM will again test this condition if the malfunction has become intermittent.
B. The BCM has commanded the fans on but the feedback voltage remains high. The BCM will command the fans off to protect the system from a possible stalled or shorted motor condition. If the control temperatures (coolant and A/C high side) should drop below the turn off points and later require the fans on, the BCM will repeat the test to determine if the malfunction has become intermittent.

Both of the above will reslut in the "Coolant Temp/Fan" telltale being illuminated whenever the control temperatures require cooling fans operation.

1. The cooling fans override feature (F.8.5) can be used to evaluate the system operation. If either fan is off when "high fans" are commanded or if either fan is on when "fans off" is commanded, the appropriate diagnostic path can be followed to isolate the malfunction.
2. The cooling fans status indicator can be used to evaluate the feedback signal being received by the BCM. If the "auto fan" indicator does not agree with the actual fans operation, circuit 791 must be investigated for a possible malfunction. If the status indicator does agree with the command fans operation within the appropriate time period, then the cause of Code F41 is not currently present.

Notes on Intermittents: If an intermittent Code F41 is being set, manipulate the related wiring while observing the cooling fans status indicator (auto fan) and commanding "High Fans" or "Fans Off" in the F.8.5 diagnostic mode. If the failure is induced, the fans status will not agree with the command operation. This will help in isolating the location of the malfunction.








Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Oct 26, 2017, 6:32 AM)






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