Intermittent error on FDC and CCP?

BONNIESPEEDY1200

MEMBER
1992 CADILLAC FLEETWOOD
4.9L
V8
2WD
AUTOMATIC
81,000 MILES

I have the car listed above FWD that has intermittent faults (codes F30 and F31) The error appears on the FDC (Fuel data center) and CCP (Climate control panel) panel is blank and doesn´t work.
But the blower works and heats/cools depending on the weather, but it is not possible to switch from defroster mode and other temperatures, panels are blank.
Every morning those panels don't work, but after 10-30 minutes the FDC display starts flash “On” and “Off”. It can do this for anything from a few minutes to 20 minutes. Then it can start working as it should. After a few minutes later CCP can start but sometimes it won't start at all.
When they both start up during the day, they work if I stop the car for a few hours. So, they work as they should. But the next day the error is repeated again.
I have changed the BCM (Body computer Module) to another one with the same result. Tried disconnecting FDC but still error on CCP, Disconnected CCP the same error on FDC. I have connected extra ground cables to FDC, CCP, BCM without any impact.
Measured with Fluke multimeter:

FDC/CCP not works: FDC/CCP works:
+ 12 V = +11, 54-13, 35 V 12 V = + 11, 56-12, 48 V
+ 16 V = +16, 4 V +16 V = + 16, 4 V
+ 5 V = +5, 05 V + 5 V = + 5, 01 V
Clock = +2, 56 V Clock = + 2, 56 V
Data = 0,246 V Data = + 0, 7-1, 0 V pulses

Have checked data cable and contacts into BCM, CCP, FDC are okay.

3 Replies

KEN L

MASTER CERTIFIED MECHANIC
42,959 POSTS

It sounds like the HVAC programmer is bad, I would try to find a used one on Ebay.

The fact that you've already replaced the BCM (Body Control Module), checked the power supply, and verified the connections is a good start. Intermittent electrical issues can be quite challenging to diagnose, but here are a few additional suggestions and insights that might help you narrow down the problem:

Grounding: You mentioned that you've added extra ground cables, which is a good step. Ensure that the grounding points are clean, free of corrosion, and securely attached. Poor grounding can cause erratic behavior in electrical systems.

Wiring and Connectors: Even though you've checked the connections, it's worth inspecting the wiring and connectors for any signs of damage, wear, or corrosion. Focus on the wiring that connects the FDC, CCP, and BCM, as well as any associated connectors.

Voltage Fluctuations: While your measured voltages seem relatively stable, it's still a good idea to monitor them while the issue is occurring. Look for any significant drops or fluctuations in voltage during the periods when the panels are not working correctly.

Circuit Board Issues: The symptoms you're describing could also be related to internal circuit board issues within the FDC and CCP. Cold solder joints, cracked traces, or other soldering issues can lead to intermittent behavior. If you're comfortable with electronics, you might consider inspecting the circuit boards for any visible issues.

Environmental Factors: Since you mentioned that the issue seems to improve once the car has been running for a while, it's possible that temperature or humidity changes are affecting the behavior. Keep an eye on whether the issue is more likely to occur during cold starts, rainy days, or other specific conditions.

Diagnostic Tools: Consider using a diagnostic tool (if available) that can communicate with the car's onboard computer systems. This could provide more detailed information about potential fault codes and real-time data from various sensors.

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Saturday, August 19th, 2023 AT 9:37 AM

BONNIESPEEDY1200

MEMBER
2 POSTS

Thanks for your time!

Is HVAC the same as ECC Programmer? If it is not, what is it?

From what I can understand and gather from the Cadillac service manual, it directs the vacuum to the dampers and the motor that controls how much hot water it should send into the heating element in the car.

Why do you think there is a fault with it, have you been involved where it has caused such a fault?
Have you replaced ECC programmer before?

I've pulled out the extra earth cable to the negative pole of the battery.

FDC and CCP circuit boards I have already examined and soldered about cold soldering and unsafe soldering.

I can't see any pattern of failure that is heat or weather related at this point.

The difference that I can see is that the data cable that goes between the FDC, CCP, and BCM shows 0.246 volts when they are not working and 0.7-1.0 volt pulses when they are working.

(My car is a Fleetwood FWD 1992, the picture you sent was of a Brougham -92)

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Sunday, August 20th, 2023 AT 6:39 AM

KEN L

MASTER CERTIFIED MECHANIC
42,959 POSTS

Here is the HVAC and programmer wiring diagrams so you can see how the system works and a guide to help you check the connections.

https://www.2carpros.com/articles/how-to-check-wiring

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