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Blower Control Module BCM Rebuild with New Heat Sink
This post documents the rebuilding of the climate control Blower Control Module (BCM) on our ’04 XJR, including new power transistor, thermal cutoff and heat sink with longer fins. Total cost was about USD $20.00, compared to the best price I could find of $200.00 for the revised Jaguar BCM, part number C2C39577. Some of this information has been previously reported by other members in several threads, and I am indebted and grateful to all who have contributed helpful information and tips. I hope this post will consolidate and supplement our collective knowledge.
The X350 BCM contains a small electronic circuit that controls the speed of the blower fan motor. Both the fan and BCM are located in the black plastic ductwork in the passenger side footwell behind the glovebox.
There has been some speculation that the BCM functions by Pulse Width Modulation (PWM), but that seems unlikely given the small parts count and absence of an integrated circuit (IC). The principal component is an N-channel MOSFET, or Metal-Oxide-Semiconductor Field-Effect Transistor, designed to handle high power (60V drain-to-source; 84A continuous drain current at 25ᴼC).
According to the 2004 Electrical Guide, battery power is supplied directly to the blower motor via a White wire from the Blower Relay (Relay 1) and Fuse 7 (40A) in the Rear Power Distribution Fuse Box; a Blue wire connects the other terminal of the blower motor to the BCM. The wire colors may vary by Model Year so check the appropriate schematic for your car. My assumption is that the MOSFET in the BCM is connected in series with the blower motor and the conductivity of the transistor is varied by a control signal from the Climate Control Module, allowing continuously-variable blower motor speed. I would welcome correction or further explanation from the electronics experts among us.
In operation, the MOSFET generates a lot of heat, so it is physically attached to an extruded aluminum heat sink to prevent component failure due to overheating. The circuit is protected by a Thermal Cutoff or Thermal Cutout (TCO), which is a type of fuse that reacts to heat rather than current. The TCO is rated to open at 114ᴼC.
Unfortunately, the original aluminum heat sink in the BCM was under-engineered, lacking the thermal dissipation to adequately cool the MOSFET under all conditions. Failure of the TCO, MOSFET, or both, is a common problem in the X350, causing immediate loss of blower fan operation. In response, Jaguar issued a revised BCM design with heat sink fins that are much longer than the originals, part number C2C39577, shown on the left in the photo below originally posted by DanJensen in the https://www.jaguarforums.com/forum/x...er-quit-62390/ thread, and used here with Dan's kind permission:
On May 27, 2009, Robert 123 (Bob) reported at jaguarforum.co.uk that he had successfully replaced the MOSFET and TCO in the BCM of his (Australia spec) 2003 X350 XJ8:
Many Jaguar Forums members, myself included, have successfully followed Bob’s procedure to rebuild their BCMs. When our BCM failed while idling in a line/queue of stopped traffic in 90+ᴼF temps, I replaced the MOSFET and TCO and all was well. That is, until a few weeks later when the TCO opened again in similar heat and traffic conditions. At that point I decided to attempt a more permanent repair, and that meant a new heat sink. Here’s how I did it:
First of all, the dimensions of the original heat sink are:
Width: 41 mm / 1.614 in.
Length: 54.15 mm / 2.138 in.
Height from base to tips of fins: 30.15 mm / 1.187 in.
Height of fins alone: 25.2 mm / 0.992 in.
After much shopping and research, I settled on an overstock heat sink from eBay, which was 57 mm high from the base to the tips of the fins, and was 64 mm wide and 102 mm long. Despite the beveled ends, it was plenty large enough to yield the final dimensions I needed.
To begin the project, follow the instructions in JTIS or the Workshop Manual to remove the glovebox. The electrical harnesses connected to the glovebox do not normally have to be disconnected; just lay the glovebox on the floor while you remove and reinstall the BCM, which is mounted atop the ductwork (green arrow).
The BCM is fastened to the ductwork with two Phillips crosshead screws. Access for a tool is limited, so to remove the screws I used a Phillips bit in a knurled thumbwheel hex bit holder.
The blower fan and motor is mounted directly below the BCM and is secured with three combination hex-head / Phillips crosshead screws that can be removed with either a socket or screwdriver. It is not necessary to remove the blower fan in order to service the BCM, but I wanted to ensure that my new, longer heat sink would not come into contact with the fan. As it turns out, there is plenty of clearance.
With the two BCM screws removed, carefully lift it out of the duct, then use a small flat-bladed screwdriver to gently pry out the tabs on the electrical connector to release the harness connector. Here’s the BCM with its original short-finned heat sink:
The tools I used for this job included, from top, a 25W soldering iron with wet sponge, thin rosin-core solder, sal ammoniac block for re-tinning and cleaning the soldering iron tip; blue plastic desoldering pump or “solder sucker”; pick for cleaning rosin and solder between joints; medium needle-nose pliers and small wire cutters; small flat-bladed screwdrivers and #2 Phillips screwdriver; small brush and tube of white thermal compound. Not shown are a wrist grounding/earthing strap, thin putty knife or palette knife, Q-tips/cotton buds, drill, tap handle and M3 0.5 tap, and disc sander or hand file.
Use your small flat-bladed screwdrivers to gently pry out the tabs that secure the top of the black plastic case. Loosen one end, then work on the other end and lift off the top to reveal the circuit board. At one end you will see a row of three solder joints that connect the MOSFET(red arrows). At the other end you will find solder joints at each corner of the circuit board that connect the TCO (green arrows). Use a desoldering pump or desoldering braid to carefully remove the solder from these five joints until the component leads are free within the circuit board holes as shown.
The circuit board can now be carefully unclipped from one of the black plastic tabs and lifted off, revealing the MOSFET (orange arrow) and TCO (green arrow). Both components are secured to the heat sink by a small metal bracket and one Phillips crosshead screw (yellow arrow). Note that the MOSFET shown is a newer replacement, which is smaller than the original. Also note that the metal bracket has been slightly modified to fold over the smaller MOSFET so that it will not come into contact with the circuit board.
Carefully remove the Phillips crosshead screw, which may be tighter than you expect, then lift out the MOSFET and TCO. The white paste is thermal compound, which improves the heat transfer between the MOSFET, heatsink and TCO. I used Q-tips/cotton buds to clean away the excess compound. The black plastic base must now be separated from the heat sink, which is firmly attached with adhesive (the white residue visible in the photo). The heat sink sits in a slight recess in the plastic base, so I had to carefully but firmly pry one corner of the base away from the heat sink before I could insert a thin flexible putty knife into the gap, then gently work it around while carefully prying the base away. Take your time and don't force things; if you break the plastic base you’ll either have to repair it or order the expensive new module, which is what we’re trying to avoid.
I shopped online for a suitable extruded heat sink with longer fins, but I couldn’t find anything with the right combination of fin height and fin density or "fin-per-inch" ratio. So I turned to eBay, and after much searching I purchased an overstock heat sink that seemed promising at USD $5.00 plus $5.00 shipping. The fin density was a little greater, but the fins were thinner so I didn't think airflow would be overly-restricted; and rather than being a solid extrusion, the fins were attached with thermal adhesive, which might slighly reduce its thermal efficiency. But otherwise it looked like it could work, and despite the beveled ends it was large enough that I would be able to cut it down to the correct footprint.
I squared up a piece of scrap plywood to use as a sacrificial holding fixture, then used existing screw holes in the heat sink to mount it to the board with countersunk screws from underneath (I had to measure carefully to position the holes so the heat sink would mount flush to the leading edge of the board and square to the blade). To cut the aluminum heat sink down to size, I used my table saw with a special blade designed for cutting non-ferrous metals. Most fine-tooth carbide-tipped woodworking blades can cut aluminum, but test carefully.
Setup was easy using the original heat sink as a sizing gauge. In addition to using the blade safety guard, which was removed for photography, I also wore safety goggles and a dust mask to protect myself from the metal chips and dust. Other tools that could be used to cut the heat sink include a band saw, sabre saw or reciprocating saw with a metal-cutting blade, an angle grinder/die grinder/Dremel with a cutoff disc, or a hack saw. The cuts don't have to be perfect or pretty, but the final size of the heat sink must fit into the opening in the top of the air duct. Also bear in mind that the smaller you make the heat sink the less cooling capacity it will have, so try to achieve a final footprint as close as possible to that of the original heat sink. I used a bench-mounted disc sander to polish the cuts on the new heat sink, then used a flat screwdriver to debur the edges.
I laid the black plastic base, MOSFET and TCO onto the new heat sink and carefully marked the position for the screw with a fine-tip permanent marker followed by a center punch. I used a drill press to bore a vertical hole through the heat sink base, then carefully threaded the hole with an M3 0.5 tap to mate with the original screw.
The total height of the new heat sink is 57 mm, compared to 29.5 mm for the original. Because of the arrangement of the fins on the new heat sink and the fact that they are glued-in rather than integrally-extruded, I had to leave a "ledge" of aluminum base on the outside edges of the outer fins so they wouldn't fall off. The resulting new heat sink was just a little too wide to fit into the recess on the black plastic base, so I used a disc sander to form chamfers on the edges so it would fit. A hand file would have worked just as well.
As far as I could tell, there was no reason for the adhesive to be thermally-conductive, and while it might be helpful for it to be heat-resistant, the MOSFET and TCO are screwed to the heat sink and soldered to the circuit board, so I wasn’t too worried about things falling apart if the adhesive were to fail. I had some plastic emblem adhesive handy, and since it is known to work with both plastic and metal, I used it to attach the black plastic base to the new heat sink.
From DigiKey I purchased the MOSFET (P/N IRF1010EPBF at USD $2.47) and TCO (P/N P10920-ND at $0.74). The MOSFET is vulnerable to damage from electrostatic discharge, so use care when handling it. I use a copper braid wrist strap that plugs into the ground/earth circuit of the household power/mains supply to drain any static charge that may accumulate on my body or tools. I test fitted the MOSFET and TCO to the heat sink and used needle-nose pliers to carefully shape the leads to conform with the holes in the circuit board. I applied a thin coat of white thermal compound paste to the back of the MOSFET and onto the body of the TCO, then mounted them with the bracket and screw, ensuring that the bracket held both components directly against the surface of the heat sink, and taking care to get the screw tight without stripping the threads. I installed the circuit board, feeding the MOSFET and TCO leads through the corresponding holes, then soldered the joints, taking care to not overheat the components or circuit board. To avoid causing cold joints, I allowed the solder to cool completely before clipping the excess length from the leads.
The black plastic cover just slips over the electrical connector terminals and snaps in place. I was concerned that the thin fins of the new heat sink (right) might ring or resonate when the blower fan was running, but I can’t detect any unusual sounds. The real test will be sitting at idle on our next 90+ᴼF day, but so far I’m calling this mod a success.
In the words of the unknown Service Manual writer, "Reassembly is the reverse of removal."
I welcome comments, corrections and questions. And please, if you choose to perform this mod on your BCM, strictly follow all proper safety procedures. Sawing, drilling, soldering and performing many automotive repairs are all potentially harmful to your body, and I have the scars to prove it!
Way to go Don!!! Thanks for the comprehensive how to on this which puts this repair all in one spot. And as we have seen this is a "just a matter of time" repair. Luckly I have the long fin version and have not heard of one of those failing yet. Not sure what year of XJ8 where the long fins were then used.
I'll be doing this repair/upgrade this weekend or next. Do you have the exact dimensions of the heat sink. I have yet to remove my module.
Hi Steve,
Welcome to the Jaguar Forums!
You've asked a great question! I had intended to include the dimensions of the OE heat sink, so I've added them to my original post, along with a link to the new heat sink I purchased on eBay and cut down to the correct size.
Fantastic post thank you. However it does not appear the eBay heatsink is still available. Does anyone have a source for a suitable heatsink? Great work thank you
Fantastic post thank you. However it does not appear the eBay heatsink is still available. Does anyone have a source for a suitable heatsink? Great work thank you
Thanks for your kind words 49Markvman.
You'll just have to search eBay for a heat sink with sufficiently long fins and a large enough base to be cut down to the correct dimensions while leaving you with at least eight (8) fins. You want a heat sink with a total height from base to the tips of the fins in the range of 45 mm (minimum) to 65 mm (maybe 70 mm maximum).
For each prospective heat sink I found, I divided the number of fins by the width of the sink, and that gave me the fins-per-inch count. I then multiplied the fins-per-inch by 41 mm / 1.614 in., which is the finished width of the original heat sink. That gave me the approximate number of fins that would remain after I cut the heat sink down to final width. If that number was 8 or greater, the heat sink was a possible candidate.
I hope this helps you find something suitable. Since I rebuilt our BCM nearly a year-and-a-half ago we have had no more problems.
No longer we need the luck of finding a heat sink on Ebay. Arctic now sells the Alpine M1-Passive. A heatsink designed to replace an active (i.d. fan driven) heat sink on the processor in your computer. I enclosed some pics.
It’s spot on! You have to do the sawing stuff Don B described and have to check the length of the fins. The Arctic fins are70mm long and might touch the fan, so maybe a bit more cutting.
The Arctic Apline M1-Passive heat sink is widely available around € 10,- at many shops on the internet
The original Jaguar BCM next to the Arctic Alpine M1-Passive
Another problem I tackled is the TCO. The one I ordered had a metal case (instead of the glass housing of the original TCO) resulting in a short from the TCO to the heatsink. As one of the three pins of the MOSFET is also connected to the heatsink (through the metal back plate), the TCO shorts the MOSFET resulting in a blower that rev’s max. The work around is to simply leave out the TCO and short the two contacts of the TCO with a piece of copper wire.
I found it a bit strange anyway to add an 80 cents TCO to the circuit to protect a $2,50 MOSFET. In my opinion you’ll need the TCO for an overheating situation and that’s probably due to the aging of the MOSFET. This problem occurs after several years of owning your Jag.
A last tip for people how have problem finding the IRF1010EPBF MOSFET in their favourite store; I used an almost similar MOSFET called; HUF75339P3. It has with 55V and 75Amp a slightly lower spec, but it is running for a couple of weeks in my 2004 XJR X350 so it might be your alternative too.
Wow. As usual, just about nothing is easy to repair on these Jags. Well, I went about rebuilding a spare blower module for my 2005 Jaguar XJ8L in which I ordered a NTE 2920 N-Channel 70A Power MOSFET, and a package of 5 Panasonic EYP-2BN109 114C 2A 250V axial leaded thermal fuses through Amazon.com. The installation of the MOSFET went straightforward enough, but when it came down to installing the thermal fuse, it took me several hours before I finally managed to secure the thermal fuse in place against the MOSFET body. This probably would have been a no-brainer had the original MOSFET been available, but since it wasn't, the thermal fuse would always fit loose in the holder. I tried adding and removing all sorts of shims, but I ended up gluing 3 small pieces of a wooden flat toothpick inside the cup of the fuse holder. Finally, that task was done, but what an absolute hassle! This was obviously a Mickey Mouse solution to a Mickey Mouse situation.
Wow. As usual, just about nothing is easy to repair on these Jags. [snip] Finally, that task was done, but what an absolute hassle! This was obviously a Mickey Mouse solution to a Mickey Mouse situation.
Hi Rickkk,
Congratulations on your successful repair. Just to put this into perspective, the blower motor resistors/control modules fail on virtually every make and model of car that use them, not just Jaguars. In the past month or so I've replaced the modules on four other makes (Audi, Hyundai, Chrysler & Isuzu). They're rarely easy to get to on any model, but the fact that you can rebuild the one on your Jag for a fraction of the price of a new one is the kind of thing many of us celebrate.
Thanks for the reply Don. What actually precipitated the problem was that the original MOSFET incorporated a heat sink that slightly projected out from the substrate of the device, but the NTE 2920 has no such projection from the body. What happens then is that the NTE 2920 creates a void that has to be filled in order to properly secure the thermal fuse. You see, when the electronic engineers designed this module, the fuse holder was fabricated to the specifications of the original MOSFET only. Filling that part of the fuse holder (with those 3 small pieces of flat wooden tooth picks) which grasps the thermal fuse seemed to be the only viable solution (although Mickey Mouse to be sure).
Hi Don & others, hopefully my symptoms sound familiar & resolvable to you all!
The past week, I noticed the fan would pulse on-off-on-off when activated full strength. Today, I noticed there was no heat / fan at all! When I push the Passenger's heated seat button, the blower again pulses instead of staying steady.
Does this sound like a BCM failure / MOSFET to you?
Hi Vanden Nate,Yes, this sounds very much like a broken BCM.
The fix is straight forward, so have a try.
Keep us updated!
Cheers, Tom
I certainly hope to try! Have to sort some cooling problems & perhaps air ride first.
Jaguar ownership has been a windy road for me, personally. I bought a pretty run-down VDP last May, and will now be on my 3rd multi-week stretch without being able to run the car. Last weekend, I noticed coolant was a bit low, so topped up the reservoir with a quart of distilled water. Did not burp or bleed the system after topping up. I have been planning to replace the thermostat and do a coolant flush, so what harm could a bit of fluid do?
Turns out, I probably put a big air bubble in the system! Overheated Thursday on my way to work, after 4 days of driving with the presumed air bubble. Towed home. Thermostat housing should be coming Thursday, so hopefully running in time for Valentine's Day
Thanks for a great write up Don, this saved me a pile of time going straight to the fix. I just repaired mine today. Here are a few notes from me "an electronics guy."
Yes, I think the mosfet is running in linear mode so it does have a pile of heat to remove. I put my meter on in frequency measure mode and got nothing which indicates no PWM. I was too lazy to drag my oscilloscope out to be sure.
I do not think the transistor is underrated. When I removed my 16 year old module the mosfet was still good, just the thermal fuse had blown. I tested the mosfet on the bench and it worked great.
Here is what I did to fix mine which is a bit bodgy but its my wife's car haha. I have a much nicer car hehe. I re-did the thermal grease on the mosfet and simply jumpered the thermal fuse. Now you may say that is risky but lets look at the failure scenarios.
1) The mosfet overheats and fails. Well they will mostly fail with a short circuit leaving the fan on high, that's okay I can demist and not be blind! The off switch still works too a I tested that.
2) The motor fails causing the overheating of the mosfet. Well if it fails properly the fuse in the trunk blows and my mosfet short circuits, still no big deal.
I will call it job done unless I get more to post about. One note is the recommended replacement mosfet was "physically smaller (TO-220AB vs TO-3P)" I don't agree with that. I chose an IXFQ94N30P3 for my first choice replacement but I didn't end up needing to buy it. The primary issue with a mosfet is not getting the heat out, so the bigger the package is the more heat it can transfer to the "air cooled" heatsink
Thank you for your post! I just realized that Photobucket has failed us once again on the photos for my original post. I'll try to upload them directly to the forum one of these days.
Since the revised BCM has significantly longer fins on the heat sink, I think it's safe to assume that the OEM engineers concluded the heat sink was insufficient, which led to my thought process on how to rebuild the unit with a new heat sink to constitute a hopefully permanent repair. We will be curious to know how long your method of jumpering the thermal fuse lasts. That could save us all even more time, effort and expense if it turns out to be a durable modification.
Robonz wrote: "Thanks for a great write up Don, this saved me a pile of time going straight to the fix. I just repaired mine today. Here are a few notes from me "an electronics guy."
Yes, I think the mosfet is running in linear mode so it does have a pile of heat to remove. I put my meter on in frequency measure mode and got nothing which indicates no PWM. I was too lazy to drag my oscilloscope out to be sure.
I do not think the transistor is underrated. When I removed my 16 year old module the mosfet was still good, just the thermal fuse had blown. I tested the mosfet on the bench and it worked great.
Here is what I did to fix mine which is a bit bodgy but its my wife's car haha. I have a much nicer car hehe. I re-did the thermal grease on the mosfet and simply jumpered the thermal fuse. Now you may say that is risky but lets look at the failure scenarios.
1) The mosfet overheats and fails. Well they will mostly fail with a short circuit leaving the fan on high, that's okay I can demist and not be blind! The off switch still works too a I tested that.
2) The motor fails causing the overheating of the mosfet. Well if it fails properly the fuse in the trunk blows and my mosfet short circuits, still no big deal.
I will call it job done unless I get more to post about. One note is the recommended replacement mosfet was "physically smaller (TO-220AB vs TO-3P)" I don't agree with that. I chose an IXFQ94N30P3 for my first choice replacement but I didn't end up needing to buy it. The primary issue with a mosfet is not getting the heat out, so the bigger the package is the more heat it can transfer to the "air cooled" heatsink"
1. Answer: The original design of the blower module was clearly deficient.
2. Answer: The reason why the thermal fuse had blown was because the MOSFET had failed. Regardless of the bench test, pick up a new MOSFET.
3. Answer: Please, don't jumper the thermal fuse as it's in there for a reason.
4. Answer: Yes, the correct replacement MOSFET (NTE 2920) is not an exact duplicate of the original , and hence the improvisation that was previously mentioned.
1. Answer: The original design of the blower module was clearly deficient.
2. Answer: The reason why the thermal fuse had blown was because the MOSFET had failed. Regardless of the bench test, pick up a new MOSFET.
The OE engineers obviously determined that the reason the MOSFET fails is due to insufficient cooling, thus the revised design with longer heat sink fins. A module rebuilt with the original shorter heat sink is not likely to last any longer than the original one did, though it may last for the remaining life of the car. I just didn't want our module to fail again on a 95-degree day while sitting in a traffic queue.
The blower module that is currently in the 2005 Jaguar XJ8L was purchased on eBay in January 2018 for around $200, and I don't recall that the fins on that particular module were any larger than the original design. However, I was in a spot as it was an especially cold winter in Michigan, and I didn't have the time, opportunity nor the luxury of hunting down a larger heat sink for the unit. Anyways, regarding the original blower module that was used in the car, I repaired that one in September of 2018 (as seen in the previous photo), and it's currently serving as a spare.
09-15-2014, 11:04 PM
Blower Control Module BCM Rebuild with New Heat Sink
