Multiple System Failure: 19+ Electrical-Related Codes in the ECM, BCM, UEM, REM, and CCM

[bryanjt]

Good morning - I'm not a mechanic by trade but I've been working on vehicles for friends and family for years now but this is the first time I've come across something like this. My sister has a 2005 Volvo S80 2.5T (Auto) that I gave her about a year ago. It previously had no check engine lights on and the last repair I did was replacing the thermostat, upper radiator hose, and thermostat housing.

In the last few days, the vehicle would act funny. She reported that it had trouble starting once (turning over but wouldn't catch), that the brakes felt weak when she first started it and tried to move (likely due to the vacuum pump), and the coolant temp sensor needle not moving from the low position.

I pulled codes, and here is what I got:

CEM (Central Electronic Module) Codes: 9C03 (Antenna signal missing), 8B01 (packing lamp signal too high), 3F02 (shift lock signal too high), 8F21 (windshield wipers signal too low), 4A37 (fuel lever sensor open or short to voltage supply), 4A33 (fuel level sensor open or short to voltage supply), 6C49 (transponder communication faulty signal), 3F90 (fuel pump relay open/short to ground)

ECM (Engine Control Module) Codes: 434C (fuel tank system leakage minor), 273D (coolant temp sensor signal low)

UEM (Upper Electrical Module): I didn't take a picture of the codes but they related to signal to the sunroof.

REM (Rear Electronic Module): 8D12 (brake lamps signal too low), 6A01 (central lock motor switch signal too high), 6A03 (central lock motor switch signal too low)

CCM (Climate Control Module): 0063 (damper motor temp right internal fault), 0060 (damper motor defroster internal fault), 00A1 (blower fan motor signal too high/signal missing), 0064 (damper motor distribution internal fault), DD30 (seat heater right no communication), DD12 (seat heater left no communication)

Most of the codes are marked "intermittent fault" in the computer.

I checked the freeze frame on some of them, but some of the data was worthless. Freeze frame on the coolant temp sensor code showed it was reading -40c for temperature. What is confusing to me is that some of the freeze frame data shows both a low voltage (0v) and a high voltage (17.5v) but I'm forgetting which codes that the freeze frame data was related to.

Since these issues are all electrical in nature, I'm thinking it's a voltage problem. I'm not thinking a ground problem because many of these problems don't share a common ground. Grounds to the body in the engine bay look good, but I haven't checked battery ground in the trunk yet. I have not replaced the alternator in the 5+ years we've owned it. We did replace the battery last year.

Besides maybe the main battery ground, I'm wondering if this could be a sign that the alternator voltage control module is failing? But from what I understand, those usually fail high (meaning it over-volts) and sometimes the vehicle and freeze frame data acts like it's getting no voltage to certain parts of the vehicle. Is it possible ECM failure?

I'm at a loss. I've never seen this many failures in the system at once. Any advice or pointers would be helpful. My sister is about to go off to college so I want to make sure the vehicle is in good shape for that. Thank you!

[Cees Klumper]

I would definitely start by checking all the battery cables and main ground connections. Sometimes a battery cable can look ok from the outside but inside it is not / corroded etc. I would also check the positive cable connection to the starter motor. Best of luck diagnosing this.