Engine/Transmission (1994 - 1998) buzzing from transmission pan

[Crowhurst]

Well, I'm back in the USA after 7 months at home in the UK. I've taken the Ram out of mothballs and taken it for its first short run. I had the seatbelt warning light on intermittently, so I separated the wiring connector under the driver's seat, sprayed it with contact cleaner, and reassembled the connector. I switched the ignition key through 2 clicks and checked that the seatbelt system was operating correctly. While my head was under the front of the seat, with the ignition on 2 clicks, and the engine not started, I heard a crackling noise from the engine area. It sounded like an arcing short circuit. Fearing that the fuel heater was burning (again), I turned off the ignition, and the noise stopped after a few seconds. I turned the key 2 clicks again, went under the truck, and the noise seems to be from within the transmission pan. It sounds like an arcing short, or a rapidly cycling relay, or a midget sending very fast morse code. The noise is erratic, like a short. I uncoupled the seatbelt wiring connector, and the noise continued. I assume that has nothing to do with the noise. Could someone please tell me that this is perfectly normal, that there is some component in the pan that is doing its proper job? Perhaps someone could tell me this, even if it's not true... ..... Thanks. Nick.

 

[Howard Durand]

I would guess that it is either the TC solenoid or the Overdrive solenoid that is clicking.

There is a multi conductor cable that emerges from the large PCM wiring harness near the center of the firewall in back of the engine and goes to the transmission.

This cable has power and control wires for the two solenoids as well as signal wires for the vehicle speed sensor.

The cable to the speed sensor is easy to find.

Follow the speed sensor cable from where it plugs into the tail piece back to where the OD/TC control wires branch off then follow that cable to where it plugs into the transmission valve body. Unplug them and see if the clicking stops. Squirt some contact cleaner into the plug and receptacle and try it again.



It could be problem with the PCM. Are the batteries at full charge?

Were they left connected during the time the truck was idle?



Try disconnecting both battery ground cables, make sure they are fully charged then re-connect them and start the truck. This may, in a sense, re-boot the PCM to it's default configuration.



The PCM may need to be re-programmed.

 

[Crowhurst]

Howard, many thanks for that. I will investigate just as you say, tomorrow morning. The batteries are at 12. 67 v, having been on a multi-stage battery maintainer while I was away. I will read the manual tonight on the relevant sections. Thanks again. Nick

 

[Crowhurst]

Howard, you are a scholar and a gentleman! When I disconnected the OD/TC connector the noise stopped. I spray-cleaned the connector ends, let them dry, and re-connected. The noise restarted. I disconnected the battery grounds, reconnected them, and the noise has stopped. I am very grateful for your help. Nick.

 

[Howard Durand]

Nick, that was sort of an educated guess. I have found that my PCM behaves differently after disconnecting and re-conecting it. It always seems to improve the shift timing for overdrive.

Also, it could have just been a poor battery ground.

Whatever the cause I am glad it solved your problem.

 

[Crowhurst]

This erratic buzzing, like a demented morse coder on speed, is still carrying on. If I do as Howard said, and disconnect and reconnect the battery grounds, the noise stops, but the next time I use the truck, the noise is back again. I have cleaned the battery top connections. The truck behaves perfectly, but these relays have a life cycle, and I don't want to burn one out. Has anyone else had such a noise, and found a long-term cure? Nick.

 

[Howard Durand]

Nick,



Sorry to hear the problem still exists. I am fairly intimate with the electrical workings of the 47RH that is in my truck but the 47RE that you have is somewhat different and I am not sure how it works.



Is the noise a buzzing sound or clicking sound?

Buzzing would indicate a loose coil or mounting of the solenoid while a clicking sound would indicate that the solenoid is being turned on and off by an intermittent connection.



There is a transmission relay in the power distribution center under the hood that is involved in your TC lockup scheme and could possibly be part of the problem. You could pull that and see if it has any effect on the buzzing. Otherwise it would appear that there is a problem with the solenoids in the transmission. Without a schematic for your truck I am only guessing but you did say that the buzzing stopped when you disconnected the wires to the transmission. Pulling the relay may help you determine which circuit is affected.



Howard

 

[Howard Durand]

Nick,

More questions on your problem.

Does the buzzing/clicking start as soon as you turn on the key or does it only occur after the truck is started?

Does the buzzing stop when either or both the OD and the TC clutch engage while driving? If so, does it take one or both to stop it?

Does it stop when the truck has been driven far enough to warm up the transmission?



If you haven't been involved in this before, you need to know that when the ignition key is turned on both solenoids are energized simultaneously through the center wire that leads to the transmission. The individual OD or TC solenoids will operate as the PCM applies ground to their respective return wires.

I believe that If you pull the "Transmision" relay in the power distribution center the TC lockup will not work. I think it interrupts the return or grounding lead between the TC solenoid and the PCM.

I refer to the PCM which is what my truck has. I think your truck has more than one computer but don't think that is an issue.

As far as the lockup solenoids are concerned, I believe the principal is the same.



You really need to isolate the solenoids for testing. You need to be able to unplug them from the truck and energize them independently. If you could find a plug with a length of wire attached that would fit the one on the transmission, apply 12 volts to the center wire from a separate source to see if they still make the noise. If it is still there, ground each of the outside wires to see if that makes any difference.

If the noise is there during this test, It will be necessary to remove the pan and go from there.

If the noise does not occur during this test you will need an electical schematic for your truck so you can determine what other components might be involved.



If anyone is reading this thread that knows the 47RE transmission please chime in if you see anything wrong in what I have said.



If you are here in the States, you might give Bill Kondolay a call at DTT. He is one who will talk to you and maybe can shed some light on this problem.

Let us know if you find out anything.



Howard

 

[Crowhurst]

Howard, many thanks for your interest. The noise is like the crackling of a short circuit, reminiscent of someone trying, badly, to arc weld. It occurs after 2 clicks of the ignition key, before the engine is started on the next click. Once the engine is started, the slight crackling is drowned out, so I can't tell if it continues. I have the full shop manual with the schematics. After looking at the relevant circuits I examined the Power Distribution Center. In the 4 years I have owned this truck I do not believe the cover has been removed, unless by the installer of a BD e-brake with Autoloc and Pressureloc. I do all my own maintenance. Schematics 8W-31-2 and 3 tell me that power goes from the battery to fuse M in the PDC, to the transmission relay, then to the transmission solenoid assemmbly, and hence to the solenoids and sensors. The Transmission relay should be switched by a signal from the Power Control Module. I removed the top of the PDC, switched on the ignition 2 clicks, and the noise started quietly after a few seconds, and then got louder over the course of a few minutes. I removed fuse M. The noise stopped. ( Remember, that when I disconnected the connector under the vehicle to the transmission solenoids, the noise also stopped. ) I then found the slot in the PDC for the transmission relay. IT IS EMPTY! Someone has bent a slave spade connector, and shorted out the solenoid slot. The connector shorts out 2 slots going across the vehicle. When I remove this connector, the noise stops. I assume that the connector shorts out pins 30 and 87, thereby giving constant power to the Transmission Solenoid Assembly, and ignoring the PCM signal to the PDC to switch the transmission relay. My spare 12v relay doesn't fit the slots. I will buy the correct relay tomorrow (Is this a dealer-only part?), fit it, and see what happens. Why would someone do this?? Too mean to buy a replacement relay? To mask a problem caused by a bad sensor or PCM signal? Any ideas?? Nick.

 

[Howard Durand]

Nick,



I dug up the TST instructions for installing the "Mystery" switch for TC control and the jumper that was installed in place of the transmission relay does indeed supply 12 volts positive to the TC solenoid. That was necessary for the Mystery switch to work properly in the later models.

From the diagram it would appear that any of the other relays in the Power Distribution Center could be used to replace the one that is jumpered. Try the one for the Air Conditioning clutch which is right above the one that has been removed.

It appears you have pretty well figured out how it is supposed to work and quite possibly the noise will disappear completely when a proper relay is inserted. The jumper may have become slightly corroded causing poor contact and low voltage at the solenoids. I am not sure why they would buzz before they were called on to operate though.

I wish I knew more about the 47RE transmissions.



Howard

 

[Crowhurst]

Howard, you were on the right track when you tallked about the mystery switch. I dug up the Autoloc installation instructions, and the relay has to be removed and jumpered. It is strange that the noise stops for a while when the battery grounds are removed and replaced to refresh the PCM. I will continue the search, and I'm very grateful for your help. You've just saved me from going up a blind alley. Many thanks, from Nick.

 

[Howard Durand]

Nick,



Obviously, something is putting a ground on the PCM side of the solenoid circuit.

Your trouble could be in the Autoloc components. When the buzzing starts, remove the jumper and connect an ohmmeter between the solenoid side and ground to see if there is any reading. If there is, see if you can disconnect the Autoloc then try it again.



Howard

 

[Crowhurst]

Thanks Howard, I'll try that tonight. Nick.

 

[Crowhurst]

Howard, I removed the jumper after the noise started, and there was no ground on the solenoid side of the relay. I tested with my ohm meter from the slot to the negative battery terminal. Infinite resistance. The noise stopped, of course, as soon as I removed the jumper. I then removed the C2 connector in the Powertrain Control Module. This contains the wires for all three solenoids, amongst others. The noise stopped, of course. I used spray contact cleaner on both sides, blew them dry, and reconnected. The noise restarted. I then removed the blue and yellow Autoloc wires which connect to the cut ends of the orange/black TCC control wire where it emerges from the PCM. I left the ends of the orange/black wire dangling, not connected. The noise continued. I need to isolate which, if any, of the three solenoids is buzzing. I am reluctant to try dismantling connectors or to cut wires, so perhaps my best bet, next time I drop the transmission pan to change the fluid, is to physically trace the noise. Nick.

 

[Howard Durand]

Nick,

I don't blame you for not wanting to cut wires or mess up any of the connectors.



DC relays or solenoids are normally very quiet. They either pull in or they don't. One thing that could cause one to buzz would be a high resistance connection to ground causing it to try to pull in but not able to draw enough current to do so or it could be due to the controller that applies the ground being defective.



The TC and OD solenoids are not supposed to operate until the ground circuit is closed either by the PCM or your controller. If one of the solenoids were shorted to ground, I would think that you would see it with the ohm meter. By the way, what does the third solenoid do?



I am assuming that the power and ground circuits all originate at the PCM. Can you pull that plug again and then apply 12 volts to the wire that normally provides power to the solenoids. That should completely isolate the transmission electrically from the rest of the truck. If the noise persists, then it looks like pulling the pan would be the next option.

If there is no noise at that point I would think it would elimiate the solenoids as the problem and possibly point to the PCM.



Aint this fun?



Howard

 

[Crowhurst]

Howard, you are a hero! Your suggestions are a great help. Yes, these things are an interesting challenge. The third solenoid in the "transmission solenoid assembly", according to the manual, is the "variable force solenoid". This is in the wiring schematics at 8W-31-3, and others, but it is not in the index, nor is it in the pages on overhauling the transmisssion. I will try your suggestion on further diagnostics tomorrow afternoon. I spent some time today, laying under the truck with my ear against the transmission pan. (I tried to make sure the neighbours couldn't see me!) The noise is coming from the front passenger side corner near where the dipstick enters. The plot thickens! Nick.

 

[Joe G.]

Does it buzz if the dip stick is pulled out?

 

[Andy Redmond]

Crow:



I think the addition of the autoloc/torqloc is causing the buzzing inside the pan (gov. solenoid area). Call BD and see what they say. .



I've installed several and this is sometimes a complaint, but BD component and other transmission components seem to work ok, so the short answer maybe to live with the noise.



You might also open the autoloc box and follow the directions for moving the DIP switch that allows the truck to turn o/d off, making you manually engaging when you want o/d. I'm guessing its set up to turn the o/d automatically at the key on cycle. If so, does this make a difference in the noise?



Good luck

Andy

 

[Howard Durand]

Joe & Andy,



Thanks for getting in on this. I am over my head with the 47RE electricals. Bad enough with the RH.

It does sound like the controller is the problem. DC relays or solenoids usually don't make any noise without help from whatever is causing them to be energized.

The truck was unused for several months prior to this trouble. Nick did not indicate that it was doing this before so I would think some contamination or corrosion could have gotten into the electronics or the connections during that time.



By the way, Nick, don't worry about the neighbors. They get used to seeing feet sticking out from under these trucks. Some of them learn new expressions of dismay as well.



Howard

 

[Crowhurst]

I'm most grateful for all the suggestions.

Joe G, yes the buzzing continues when the transmisssion dipstick is removed. The sound is like an electrical arcing, a harsh varying crackling. Think of a mouse using an arc welder inside the transmission!

Andy Redmond, I'll submit this to the BD-power forum today, and let you know the response. I have always had the inverter option on the Autoloc, so I have to manually select overdrive. I prefer it like that, especially when towing.

Howard, I don't know when this noise started. As it is only heard when the ignition switch is on 2 clicks, but the engine has not started, this noise could remain unnoticed for years. The only reason I discovered it was while dealing with a seat belt solenoid whose connections needed cleaning.

I'll let you know of any progress, and thanks again for all your help. Nick.