P38 Fuse Box Repair and Replacement

fbox_complete1.jpg - 12122 Bytes Introduction
Symptoms and Diagnosis
Replacing the Fusebox
Dismantling and Repair

 

 

Introduction

The engine compartment fuse box on the 4.0/4.6/P38 is positioned behind the battery, so in addition to the usual heat cycling stress in the engine compartment, it is subject to corrosion problems due to corrosive vapors from the battery making their way into the fusebox. Keeping your battery terminals clean and the battery maintained helps to avoid the corrosion problem. Another problem can be spilled coolant getting into the fusebox. Photos below show the effect of this. We recommend covering the fusebox with plastic before filling the header tank with coolant.

Although fusebox problems can lead to a variety of weird symptoms (sometimes even leading you to think there are BECM issues), the most common problem is HEVAC related due to burning out of Relay 7 and its mounting terminals. There are different theories about why this happens; I have heard from several Rover techs including Chris Schaeffer, an ex-Land Rover mechanic, that the most frequent immediate cause of burned out terminals on the fuse box is clogged pollen filters imposing additional load on the climate control system blowers. He advises changing the pollen filters much more frequently than the recommended 30,000 miles to prevent this. (See the Pollen Filter Replacement page to find out how dirty they get even in normal street use). However both Ron Beckett, who is an electronics technician, and I (an electrical engineer) have doubts about this as reduced airflow normally reduces the load on any blower or pump. Thomas Dirksen found a more logical cause -- a loose primary wire on the Left Hand blower motor which, when bouncing during offroading, would intermittently make contact, creating not only an arcing condition at the blower motor but on/off surges at the RL7 relay.

 

If your fusebox does eventually give up, instead of replacing it you can repair it using the following ingenious illustrated procedure supplied by Ron Beckett.

Symptoms and Diagnosis

Note that fusebox problems can cause a variety of symptoms. Althought the most common are in the hevac system,  ou can also get strange things happening that look like BECM failure (see below). Even experienced mechanics can be fooled by this, thinking the BeCM needs replacing -- every 4.0/4.6/P38 owner's nightmare. Instead the problem can often be cured at minimal cost.

Hevac Problems and RL7 Failure
The most common problem in the fuse box is failure of the relays that power the electric fans -- particularly RL7. You can inspect the relays at the front of the fusebox for signs of burnt or discoloured spots on the housing.  Burned out relays or circuitry will cause intermittent HEVAC operation. Ron Beckett found that not only the relay but the underlying terminals were affected due to the heat. Because the HEVAC display had illuminated the book symbol, Ron had a check done with Testbook to find out what was the cause; Testbook indicated a number of reasons, one of which was a faulty relay RL7.  So he pulled RL7 (which controls one of the heater fans) out of the engine compartment fuse box and found the fuse box itself was charred and that the output terminal was loose.  It seemed as if the circuitry was not up to the task. (Ron reports that the check book symbol on the dash comes on for a number of faults -- the faulty relay will be logged as a fault in the HEVAC and it will be specified as RL7 in the fault-finding.  Ron has played with the LR Testbook and seen that logged fault on his car.  The check book symbol will clear when you turn the car off but will reappear the next time - maybe not immediately but it will reappear).

 

Ron also found that with RL7 having failed, the air conditioning did not provide very cool air. Discussions with the airconditioning serviceman who was visiting the workshop gave an explanation. The serviceman suggested that there was insufficient airflow over the evaporator. After the fusebox was repaired, the air conditioning once again gave good performance - particularly important as the temperature at Ron's home town when this was written was 42 deg Celsius or 107 deg F. Another side affect of the repair is that the air conditioning condensor fans in front of the radiator are working once again.

The pictures below show a heat-affected relay. When Ron pulled the yellow cover off the relay, he found that the plastic base had melted sufficiently for the internal relay contact to move so that even though the relay still operated, it no longer completed the circuit. Once the relay pins have overheated, they will only get worse.  Replacing the relay is only a very short term solution -- the bad contact between the relay terminal, the socket, and the burned PC board, will cause overheating and damage the new relay.

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Fuse box heat damage at RL7 Note adjacent RL6 mount is undamaged.

Melted relay RL7 base.

Relay RL7 internal view.

Note on Causes: Clogged pollen filters are commonly blamed for this RL7 problem, but that makes little sense as it would reduce the load on the blower motors. Also Thomas Dirksen has astutely observed that if the pollen filter hypothesis was correct, both left and right blower motors would be equally affected, ie RL7 and RL6. However nearly all problems seem to be with the left one (RL7) alone. In Thomas's case the cause was a loose wire on the motor itself; this would be well worth checking on to avoid a repetition of the problem. For access to the blower motors, see the pages on HEVAC Blend Motor Replacement and Dashboard Removal and Replacement.

Random Cranking
Simon Goode reports on some other symptoms that could mean possible fuse box failure.

"The first was one very strange fault.  After putting in a new battery when I got the car, I parked it at home and then the next morning I awoke to hear the starter motor cranking over!   It went for about 5 secs, then off, then on again for a couple of seconds.  Very alarmed, I disconnected the battery.  I took the car to the mechanic that day and it was plugged up to look for any codes.  Only climate control codes came up - but that's another story!"

"The dealer had no other ideas except to replace the BeCM.  So I decided to take the car home again and to look into it myself.  I left it parked at home for 2 more days and had no cranking at strange times - maybe the computer just needed resetting?  But then the next morning at about the same time, it did it again."

"But this time it just kept on cranking until I removed the starter relay. After testing the voltage at the relay coil I found it to be about 9 volts and when I moved my hand and bumped another relay it dropped to 0 volts.  So after reading your fuse box repair page I did just that.  I removed the fusebox to find lots of corrosion and one of the blower motor relays burnt out. I cut all the links to open up the PCB and clean it and repair the burnt track.  I then desoldered the links and replaced them all with new copper wire.  I put it all back together and it's been good for 2 weeks now!"

"Gearbox Fault" and Complete Power Blackout
Some owners have reported more serious symptoms involving power failing to the whole vehicle. For example,  Walter Gates reports  experiencing sudden, temporary complete power failure three times over approximately five months.  The first two times the engine stalled and a "Gearbox Fault" message appeared on the message center. (This message means power supply to teh gearbox is low). The third time the engine did not stall but the fault message appeared.  The first two times the power returned and the "Gearbox Fault" message cleared.  Walter also noticed that when the turn signal lights were blinking the background light on the HEVAC readout panel would dim or flicker.  Tellingly, there was also an odor of an electrical short in the engine compartment fuse box, even though all the fuses were good. Finally, Mr. Lucas struck with a sudden, complete and permanent power failure.  Because of the brake-transmission interlock switch, he could not even shift the transmission into neutral to roll the truck on to a flatbed tow truck.  The tow truck driver was clever enough to crawl under and disconnected the shifter so he could manually shift the transmission into neutral.  Upon inspection of the Engine Compartment Fuse Box, there was now an extremely strong odor of an electrical short.  The problem was quickly found.  The Positive power connection post was completely burned off where it meets the fuse box board!

Symptoms that Emulate BeCM Failure
Problems in the engine compartment fusebox can simulate BeCM issues, like the random cranking above, and other starting problems that look like the engine is disabled by the alarm system. Brian Schauf of Dealer Direct Auto worked on a 1998 HSE that was stopped and idling when the vehicle just died and would not turn over at all. Power seemed to be on and everything like the windows and such worked fine. On turning the key there were no error messages although the message center said none of the windows, lift gate or sunroof were set. "The only error message I get is when I set the alarm and try to turn it over: "Engine disabled use remote". The Engine light comes on and goes off before I try to start it. The remote will unlock and lock the doors, except the passenger side front door  and arm/disarm the alarm. I have tried the generic EKA procedure #1515 with no avail. When turning the lock, the side lights will blink so I think it is recognizing the input although the lock seems to be a little loose. We have tried unhooking battery and hooking back up with key in #2 position as well. Fuses and relays seem to be fine. We have replaced the remote batteries and made sure the vehicle battery is fully charged as well. When we turn the key, there is a click noise from the controller under the passenger side seat and that is about it. I feel it is in the alarm system but am having absolutely no luck!"

A week later Brian wrote back in with the following news: "We took the fusebox apart and repaired it from the info you provided and it worked! We found all kinds of solder joints that needed repairs and once we repaired them the Rangie started up and runs excellent. I was very grateful that it was not the BECM!"

Fusebox Replacement

Your options are either replacement or repair. If you choose repair, see the dismantling and repair section below. If you choose replacement with a new one, it is an easy operation. The plugs underneath simply unclip.  You have to depress the locking tab then pull them out. However, there are a couple of things would should do before disconnecting the battery.

1. Make sure the car keys are in your pocket, not the car.  When you reconnect the battery, the car will lock itself.  I also leave a window open - just in case.

2. Make sure you have the radio code.

Ron discovered that a new fuse box is A$380 (about US$250 or GBP150) for one without relays but including fuses and battery cable so he decided to see if he could repair the old one himself. (Should you decide to just replace yours, I found new ones at Import Parts Bin (Speedy Car Parts) for about US$220 with free shipping).

The fusebox underwent several minor design changes over the life of the 4.0/4.6 series of Range Rovers. Ron Beckett has identified five fuseboxes during the life of the vehicle (the first three for petrol  - the later diesels had different fuseboxes). He reports "To VIN VA346793, the fusebox part no. was AMR3376 or AMR3375 - I have two parts lists with differing numbers - and both are LR publications.From VA346794 to VIN VA376579, the fusebox part no. is AMR6405 or AMR6406  - again the numbers differ depending on the publicatio. From VIN WA376580  (WA is the '98 model year, which started in July 97), the part no. is AMR6476 or AMR6477 - yet again the numbers differ depending on the publication.  There are yet more variants of the fuseboxes for the later diesels.)"

 

It is not completely clear whether the later part nos. replaced the earlier one because of the problems described on this page, or if there were electrical system changes which required a new design.  It would also be interesting to know if any cars with the later fusebox have had the problem.
 

Regarding the relays, there is a difference between the yellow AMR2548 (no longer available; Ron tried to buy one recently and it had been replaced by a new part number YWB10012L which are supposed to be yellow but the one I received was a black one) and the green relays AMR2547 (now YVB10031).  The green relays are change-over relays and have 5 pins, the yellow ones have only 4 pins and are a make-set (normally open).  The yellow relay will plug into a green socket but not vice versa.

 

Dismantling & Repair

To remove the fusebox, disconnect the battery leads (always remove the earth/ground lead first - then it won't matter if your wrench shorts across from the positive terminal to the body. Remove the fusebox cover and undo the nut holding the battery lead onto the stud (see below).

Remove the three bolts holding the fusebox in place and carefully turn it over to access the connectors underneath.  Depress the protruding clip on the connectors and gently work them off the box.  (Note these pix are for an early fuse box. Later ones changed but Ron is unsure of the changes made to the fuse box.)

Unbolt the three BECM power cables from the bottom of the fuse box, noting their colours and to which stud they are attached. The nuts (see arrows) are captive on the power leads so you won't lose them.

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Unbolt battery lead from fuse box.

Underside of fuse box - power leads arrowed

With the fuse box out and on the bench, note the location of every relay and fuse. If possible, take a photo for reference. You'll note from Ron's pix below that his fuse box is not fully populated with relays and fuses as Australian delivery HSEs were not fitted with heated windshields. SE models may have different relays, too, depending upon the options fitted.

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Only RL7 (lower right) has been removed. Note broken left hand side of fusebox.

All relays and fuses removed to allow removal of the cover panel over the printed circuit board.

Now come the delicate bits - removal of the printed circuit board (PCB) from the case which may be embrittled by years of high underhood temperatures. Refer to the pix below. Remove the 5 Phillips head screws and carefully lift off the panel that you can see - the one with the relay numbers and the green and yellow stripes.

Removal of the lower case requires gently levering the clips located around the sides of the case and prising the case off the PCB whilst simultaneously pressing on the three BECM power studs and the pins of the connectors on the bottom of the case. Once the PCB has started to move you can gently work it out of the case by pressing on the studs and pins underneath.

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Remove 5 screws (yellow arrows); release clips (brown arrows).

Once the board is out, you'll soon see the damage - see pix below. Note also the discolouration of the PCB near RL12, the fuel pump relay. Close examination of the pin showed that the gap (arrowed) in the pin for the blade of the relay it was slightly wider so it hadn't been making good contact and had overheated. Note the corrosion from coolant that had been spilled into the fusebox

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Corrosion from coolant spilled into the fuse box. Note broken side of fuse box casing - this is the side closest to the coolant header tank.

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Above: Relay side of fusebox showing location of damage. Also note discolouration around RL12.

Below: Cable entry side of fusebox

Above: Close-up of burnt section of fuse box at RL7

Below: Relay terminal socket that fell out

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After pulling the box apart, Ron found that the terminal into which the relay plugged was more than loose. It just fell out.  But he couldn't solder it back in because the fuse box consists of two printed circuit boards folded back-to-back (naturally with the solder sides together) and joined down each end with a string of through-board links (below).

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Links between fuse box circuit boards

Cut links to enable....

....opening up of the boards.

It is impossible to remove these links without damaging the board so Ron took the "easy" way out and cut them all in half so he could open the boards up to access the solder sides. Once the boards were opened, he carefully desoldered the pins, filed them flat to the PCB track, and then punched the pins out from the copper side (to avoid lifting the copper off the PCB material).  Upon reassembly, he replaced all the links with heavy gauge copper wire.  He believes this is more reliable than just bridging the cut links.

However, care has to be take to avoid breaking the PCB when punching out the remnants of the pins. Ron took a short piece of wood and cut a longitudinal 1/16" (1.6 mm) slot close (about 1/4" - 6mm) to the edge of the wood with a handsaw. The slot was positioned under the row of pins to give the pins somewhere to go when they were punched down. The flat surface of the timber supported the PCB on either side of the row of pins - see below. Ron used a small nail (with the point filed off) as punch then gently tapped the nail with a tack hammer.

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Links filed flat then punched out from the track side of the PCB. The piece of wood was slid under and the row of pins fitted into the slot in the timber. This supported the PCB and prevented it being fractured when the pins were punched out.

Due to the charring of the PCB, it would have been pointless just resoldering the relay socket terminal.  The socket needed mechanical support to prevent it just being pushed away when the relay was reinserted.

 

Ron suggests two ways of making the repair. If there is a sufficient undamaged original PCB to provide support for an overlay of new PCB, then this is the better way to do the repair. Cut a small piece of PCB (or similar non-conductive material about 1/16" thick - Ron used 1/16" fibreglass PCB) sufficient in size to cover the damaged area and to be able to get support from the surrounding good PCB.  Drill a small hole, just large enough for the shoulder of the pin (see picture of socket pin in first set of photos above) to pass through and to allow the bottom of the pin to still reach the PCB track underneath the board.  Epoxy or superglue the new piece of material in place on the top side of the board.   After cleaning up the pin and the track, resolder the pin in place.  Fill the hole around the reinforcement piece with epoxy or superglue and micro-balloons.

 

However, in Ron's case, he did the repair before he thought of the method above. As a result, the method he used is illustrated in this article, He removed the damaged section of board by careful filing to get back to good undamaged PCB. He then cut a piece of 1/16" fibreglass PCB (without copper) to fit the hole. He glued this piece into the hole with high temperature super glue and also glued the PCB track down to the fibreglass repair section.

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Burnt section of PCB removed and hole prepared for a plug. The original PCB track can be seen through the hole.

The plug of PCB material inserted and glued into place. A reinforcing piece over the joint would have been a good idea.

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Completed repair with the pin soldered into place.

New heavy guage wire links between the two PCBs

Another trick employed by Ron (after removing the PC board lacquer on the tracks at risk) was to beef them up with a thick layer of solder to increase the current carrying capacity of the track.  The track is probably undersized for the current draw and this may explain why only RL7 seems to be affected. 

After cleaning the boards of what appeared to be some brown muck (water-based flux perhaps?) and refitting the wayward terminal and resoldering it, Ron closely examined all the joints with a high-power magnifying glass.  As expected, he found a number of cracked solder joints.  All were for the terminals for the plugs that fit under the fusebox.  Ron soldered them all up and reassembled the fuse box.  He is hoping this will cure some odd electrical problems!!

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Close-up of cracked solder joint on terminals for plugs under fuse box.

The black mark near the cracked solder joint was so Ron could find it again through the camera lens!

Bruce Powell did the repair following these instructions and found it took about 2 1/2 hours and worked perfectly. He found a couple of the yellow relays were burnt also.

 

 

 


 

 

 

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Page revised February 2, 2012