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I took the rear bumper off last year looking for a cut in the RDC wires. I didn’t find anything.
Ha! I need to look at my notes and see if I had those K-Can line faults back then.
Peter
Good luck with the fix, Peter.
Keep in mind that if unplugging the RDC module eliminates D904 but no damaged RDC K-CAN wires are found, the RDC module may have an internal wire or circuit fault that is responsible for the fault code. Also inspect the RDC module for water damage, which is quite common.
Ha ha! I was so focused on the A/C work that I forgot that I had the two K-Can line faults last October when I replaced the battery. I paid a Mini technician on Just Answers.com who told me that it doesn't cause any problems ands to stop worrying about it.
I'm not too stressed then; however, I think I will unplug the RDC and see what codes show up.
I think I will unplug the RDC and see what codes show up.
Unplugging the RDC module will result in fault code A3C3 (Instrument cluster: Tyre pressure control, communication fault). But if D904 disappears, you're on the right track.
Wait. I forgot an important detail that makes testing the potential role of the RDC module in causing D904 much easier. Simply remove fuse F19 (source of power for the RDC module) and then check whether D904 disappears.
Last edited by Maybe, maybe not; Aug 24, 2025 at 04:50 PM.
I pulled fuse 19 and got no D904 code. I did get C913 (JBE no message), A3C3 (Tyler pressure communication fault, E735 (No message, wiper IHKS etc.), A0B1 (CAS input implausible). What does this indicate to you?
With high certainty, the RDC module is faulty or the RDC module K-CAN wires are damaged. Inspect both. If you don't find damaged RDC K-CAN wires, a faulty RDC module should be considered first. I have a working RDC module (shown in previous post) that I can send to you.
The new codes are almost surely due to removal of F19 because this fuse also supplies voltage to other systems.
I went to LKQ (local salvage yard) and pulled another RDC aerial and the harness from the back of the car. Replacing the RDC unit didn’t change the fault code. It is still D904. I’m going to look at replacing the harness on the rear bumper now.
D904 fault is cured. No more faults. I found a tiny hole in a green K-Can bus wire that bled green corrosion. I picked up two rear bumper harnesses and one matched so I spliced it in (solder wires, heat shrink, over wrapped by electrical tape).
I’ve made a mess several times while working with freon so ended up writing out how to avoid the mess and excessive loss of freon. I tried to get the correct freon by watching the pressures but added way too much.
I have additional A/C-related questions.
What were the signs that made you realize that the A/C system had been way overcharged with refrigerant?
Was the engine struggling?
Was the compressor struggling?
Was the drive belt slipping?
Did the compressor clutch fail to engage?
Were the manifold gauge low and high pressure readings both unusually high?
Or was it something else?
The Mini under hood badge said 1.02lb of R134a but I charged looking for ideal pressures. After I put too much in, the low pressure was still too low. I decided to drain it out and put the correct amount in instead of looking for standard pressures. It didn’t have problems, I just wanted it right after all of the work I did.
When charged with the correct amount of freon, my low pressure was a low 31psi where I would expect 35 to 55 psi. The high was okay at 215psi where I would expect 150 - 250 psi high (@75F).
Peter
The Mini under hood badge said 1.02lb of R134a but I charged looking for ideal pressures. After I put too much in, the low pressure was still too low. I decided to drain it out and put the correct amount in instead of looking for standard pressures. It didn’t have problems, I just wanted it right after all of the work I did.
When charged with the correct amount of freon, my low pressure was a low 31psi where I would expect 35 to 55 psi. The high was okay at 215psi where I would expect 150 - 250 psi high (@75F).
Peter
Aside from the 85F ambient temperature, what are the specific conditions when you measured 31 psi low and 215 psi high?
For example, when I check MINI A/C pressures, the A/C has been running for at least 10 minutes in a shaded garage (ambient temp 90-95F) with recirculation off, doors and windows open, engine idling normally, and a large fan blowing air over the condenser and engine bay. I do this so that I am reading the pressures under harsh conditions where the A/C compressor must run constantly.
The Mini under hood badge said 1.02lb of R134a but I charged looking for ideal pressures. After I put too much in, the low pressure was still too low. I decided to drain it out and put the correct amount in instead of looking for standard pressures. It didn’t have problems, I just wanted it right after all of the work I did.
When charged with the correct amount of freon, my low pressure was a low 31psi where I would expect 35 to 55 psi. The high was okay at 215psi where I would expect 150 - 250 psi high (@75F).
Peter
When charged with the correct amount of freon, my low pressure was a low 31psi where I would expect 35 to 55 psi. The high was okay at 215psi where I would expect 150 - 250 psi high (@75F).
Below are the standard R134a low- & high-side chart that I have used for my cars with fixed displacement compressors.
At 75F, this chart shows 35-45 PSI on low side and 150-170 PSI on high side. Maybe your gauge test was done @85F rather than @75F?
I think there is still some research to be done on the variable displacement compressor influence.
I don't think there's any debate about the differences between old fixed displacement compressors and newer variable displacement compressors, which do not fulfill our outdated expectations found in automotive low- and high-side R134a pressure charts.
But you can decide for yourself. Watch some Tom Lech videos on variable displacement compressors. He an automotive A/C expert and 3rd generation in an A/C family business.
Did you happen to use the Walmart 12-oz R134a can below for your Mini A/C work? If so, did you happen to compare the full versus empty weight of the cans?
The weight I measure for the full cans is 438 grams. If the cans contain exactly 12 oz of refrigerant, then the weight of R134a in the can would be 340 g, which would mean that the empty can weighs ~98 g.
In post #16, you mentioned that "There will probably be 326g freon in a can". Is this the actual weight of R134a in the can or was there some refrigerant left in your cans?
