differential interlock mechanism warning light
10-29-2002, 05:38 PM
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differential interlock mechanism warning light
The warning light that looks like the two connected differentials came on while I was drifting a corner on track. The manual says this is the interlock mechanism warning and if it comes on you should adjust your driving to the changed driving characteristics of your car and to consult your Porsche dealer,or something like that (I don't remember word for word).
After re-setting the computer by turning the ignition off and on the warning did not re-appear.
What is this interlock mechanism? And does the warning mean something has failed even though it did not come back on after reset?
It did seem like I couldn't put as much power down on corner exit while the warning was on. Sort of like not having a limited slip differential.
chet
After re-setting the computer by turning the ignition off and on the warning did not re-appear.
What is this interlock mechanism? And does the warning mean something has failed even though it did not come back on after reset?
It did seem like I couldn't put as much power down on corner exit while the warning was on. Sort of like not having a limited slip differential.
chet
10-29-2002, 08:10 PM
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Chet... what year is your C4? I've been learning more than I want about this characteristic of C4's. Has your car been a daily-driver? Or, has it sat for any extended period in the last few years?
10-29-2002, 08:38 PM
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Its a 1993, pretty much stock except for lowered suspension (springs & shocks). It was a daily driver up until I bought it at 82,000 mi and i've put on another 10k mostly track and commuting to/from track.
The owner's manual has very little info, which is vague at that. Especially since the warning light comes on with the alarm sounding as well.
The owner's manual has very little info, which is vague at that. Especially since the warning light comes on with the alarm sounding as well.
10-30-2002, 02:57 AM
#4
cbottone:
When the interlock light on the instrument panel comes on it's considered a "priority 1" problem. The lights, alarms, etc. come on in priorities of 1 through 3, with 1 being serious. Resetting the DME won't correct this. Odds are the problem was temporary and went away on it's own, but that doesn't mean it should be ignored.
Possibly you may have been a little low on brake fluid, or perhaps you boiled your brake fluid. This would explain why the problem went away temporarilly. The AWD system relied on brake fluid for more than just braking. You may also have air in the system.
I would contact a shop and see if they can use a Hammer on it to retrieve any codes that might have triggered this. It may be trivial, but it may be serious as well.
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
When the interlock light on the instrument panel comes on it's considered a "priority 1" problem. The lights, alarms, etc. come on in priorities of 1 through 3, with 1 being serious. Resetting the DME won't correct this. Odds are the problem was temporary and went away on it's own, but that doesn't mean it should be ignored.
Possibly you may have been a little low on brake fluid, or perhaps you boiled your brake fluid. This would explain why the problem went away temporarilly. The AWD system relied on brake fluid for more than just braking. You may also have air in the system.
I would contact a shop and see if they can use a Hammer on it to retrieve any codes that might have triggered this. It may be trivial, but it may be serious as well.
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
10-30-2002, 10:49 AM
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Bill, I'm not saying you're wrong, but brake bluid shouldn't affect the differential warning light, should it? 
When my problems arose with this light, Adrian said the following in part:
[quote] The differential lock is not disengaging correctly. This is normally caused by old fluid, or gunged up diff lock pressure regulator. The diff locks could also be worn... This work must be done using a Bosch hammer... I would recommend that you get a full system flush, bleed and interlocks check... You might also wish to look at the transmission fluid level.
<hr></blockquote>
I'm having this done on November 4th... I'll let you know what happens.
When my problems arose with this light, Adrian said the following in part:[quote] The differential lock is not disengaging correctly. This is normally caused by old fluid, or gunged up diff lock pressure regulator. The diff locks could also be worn... This work must be done using a Bosch hammer... I would recommend that you get a full system flush, bleed and interlocks check... You might also wish to look at the transmission fluid level.
<hr></blockquote>
I'm having this done on November 4th... I'll let you know what happens.
11-01-2002, 07:55 PM
#6
The 4WD system is actuated with brake fluid, so old or boiled brake fluid can cause the fault.
Changing the fluid on a C4 is a hour to hour and a half job as the clutch, brakes, brake booster system and 4WD has to be bled.
Changing the fluid on a C4 is a hour to hour and a half job as the clutch, brakes, brake booster system and 4WD has to be bled.
11-02-2002, 02:49 AM
#7
Bob:
The fluid Adrian is talking about IS brake fluid, with the exception of his very last comment where he says you might want to check your transmission oil as well. The ABS system and the AWD system work in conjunction with each other. In fact, if you've ever read the old article in "Excellence" magazine called "Wringing out the C4" (or something like that), the writers talk about deliberately applying the brakes on the C4 hard enough so that the ABS system kicks in because this in turn disables the locks and reduces understeer.
If you have a set of manuals, the two sections dealing with the AWD and ABS system are combined as one section numbered 39/45 and called "All Wheel Drive/Antiblock System". The locks are controlled by hydraulic pressure from brake fluid. The whole system has it's own computer which delegates where the highly pressurized brake fluid is to be channeled.
The system is quite complex.
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
The fluid Adrian is talking about IS brake fluid, with the exception of his very last comment where he says you might want to check your transmission oil as well. The ABS system and the AWD system work in conjunction with each other. In fact, if you've ever read the old article in "Excellence" magazine called "Wringing out the C4" (or something like that), the writers talk about deliberately applying the brakes on the C4 hard enough so that the ABS system kicks in because this in turn disables the locks and reduces understeer.
If you have a set of manuals, the two sections dealing with the AWD and ABS system are combined as one section numbered 39/45 and called "All Wheel Drive/Antiblock System". The locks are controlled by hydraulic pressure from brake fluid. The whole system has it's own computer which delegates where the highly pressurized brake fluid is to be channeled.
The system is quite complex.
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
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11-02-2002, 08:08 AM
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Bill,
Is the hydraulic system for the clutch also part of this system as since havnig my brakes serviced, it is sometimes a little harder to get into gear?
Andy
Is the hydraulic system for the clutch also part of this system as since havnig my brakes serviced, it is sometimes a little harder to get into gear?
Andy
11-03-2002, 04:46 AM
#9
Andy:
The answer is (for C4s) yes and no (can't lose with an answer like that!
)
The clutch uses the same fluid resevoir as the brake system to supply fluid, but the hydraulic circuit is separate from the ABS system and looks like it's functionally a typical master cylinder setup...it just doesn't have your typical "cup" sitting on top of the master cylinder, and it's not pressurized like the ABS system is.
As far as your problem goes, possibly during the bleed some air managed to get into the clutch hydraulics.
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
The answer is (for C4s) yes and no (can't lose with an answer like that!
)The clutch uses the same fluid resevoir as the brake system to supply fluid, but the hydraulic circuit is separate from the ABS system and looks like it's functionally a typical master cylinder setup...it just doesn't have your typical "cup" sitting on top of the master cylinder, and it's not pressurized like the ABS system is.
As far as your problem goes, possibly during the bleed some air managed to get into the clutch hydraulics.
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
11-05-2002, 09:53 AM
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Dear Chet,
Interlock is the traction control system. This system as well as the ABS, brakes and clutch use BRAKE FLUID. You check the transmission fluid level which is not brake fluid to see if one of the diff locks is leaking brake fluid into the transmission fluid. The only link between the brake fluid and the transmission fluid is the differential lock. I have known of a number of cases where the internal seals of the locks had failed and when activated and only when activated they pumped a little fluid into the transmission.
The diff lock also slipped and activated the warn light.
Working on the brakes, especially on a C4 can have an affect on the clutch hydraulic if the job is not done properly. Hence the comment, follow the procedures in the maintenance manual especially for a C4.
Hard to select gears is not unknown for many other reasons as well. Gearbox very hot is the most common cause.
Low brake fluid level is something easily checked.
I have sort of given up trying to help people with these problems. I just say use the maint manual or wait for my book. There are many technical articles onthis subject on the tech page and many more items in the archives. Almost every person with this problem has something different wrong with their C4.
What you must do is to show the following when you post.
1/. List all warn lights that come on.
2/. Indicate if the warn horn activates.
3/. Explain exactly when the warn lights activate. Either stay on after start and never go off. Go off and come back on before driving off or come on whilst driving.
4/. If possible indicate at what speed this happens.
Ciao,
Adrian
911C4
Interlock is the traction control system. This system as well as the ABS, brakes and clutch use BRAKE FLUID. You check the transmission fluid level which is not brake fluid to see if one of the diff locks is leaking brake fluid into the transmission fluid. The only link between the brake fluid and the transmission fluid is the differential lock. I have known of a number of cases where the internal seals of the locks had failed and when activated and only when activated they pumped a little fluid into the transmission.
The diff lock also slipped and activated the warn light.
Working on the brakes, especially on a C4 can have an affect on the clutch hydraulic if the job is not done properly. Hence the comment, follow the procedures in the maintenance manual especially for a C4.
Hard to select gears is not unknown for many other reasons as well. Gearbox very hot is the most common cause.
Low brake fluid level is something easily checked.
I have sort of given up trying to help people with these problems. I just say use the maint manual or wait for my book. There are many technical articles onthis subject on the tech page and many more items in the archives. Almost every person with this problem has something different wrong with their C4.
What you must do is to show the following when you post.
1/. List all warn lights that come on.
2/. Indicate if the warn horn activates.
3/. Explain exactly when the warn lights activate. Either stay on after start and never go off. Go off and come back on before driving off or come on whilst driving.
4/. If possible indicate at what speed this happens.
Ciao,
Adrian
911C4
11-05-2002, 10:12 AM
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I had Chris Powell of Chris's German Auto Service of Belleuve, Wa work on my C4 yesterday. Forgive my ignorance on terminology, but this is what he said...
He said he bled the differential locks and found some air in the lines. When he used the Hammer, he found no fault codes (which was nice to hear.) He then had me take it for a hard drive and see if I could duplicate the light-on/shudder problem. I found a 90% decrease in the previous shudder problem even though the light still goes on. The light SHOULD go on, of course, when my car senses a loss of traction, etc., but the dissengaging of the interlocks shouldn't vibrate hard.
He did say that if it acted-up after I got home that the next step was to have the "engagement pressure" checked on the interlocks. As it is a very high pressure system, it requires a special gauge to do this.
Just thought I'd post my individual findings
He said he bled the differential locks and found some air in the lines. When he used the Hammer, he found no fault codes (which was nice to hear.) He then had me take it for a hard drive and see if I could duplicate the light-on/shudder problem. I found a 90% decrease in the previous shudder problem even though the light still goes on. The light SHOULD go on, of course, when my car senses a loss of traction, etc., but the dissengaging of the interlocks shouldn't vibrate hard.
He did say that if it acted-up after I got home that the next step was to have the "engagement pressure" checked on the interlocks. As it is a very high pressure system, it requires a special gauge to do this.
Just thought I'd post my individual findings
11-05-2002, 10:28 AM
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Dear Bob,
Depends which light you are talking about. The yellow led should flash on. This is located on the centre console above the traction control ****. If somebody has hooked up the green lamp in the main cluster (I do not recommend you do this) this will also flash. The red light or warn light is NOT supposed to come on. I am assuming and hoping you are talking about the yellow light or led.
Air in the traction control system lines will not give you a fault code but it sure will give you a shudder. As will very old fluid.
The rest of the shudder may well be a wron diff lock. The material on the disks themselves may be wearing off. You will mos tlikely have the old Valeo material ones. I know from personal experience that the newer material units which I have installed in my C4 because my diff locks wore out are quieter and smoother than the old ones. However 90% is better than nothing. I still hope your red warn light is not coming on. Please confirm it is the yellow led.
Ciao,
Adrian
911C4
Depends which light you are talking about. The yellow led should flash on. This is located on the centre console above the traction control ****. If somebody has hooked up the green lamp in the main cluster (I do not recommend you do this) this will also flash. The red light or warn light is NOT supposed to come on. I am assuming and hoping you are talking about the yellow light or led.
Air in the traction control system lines will not give you a fault code but it sure will give you a shudder. As will very old fluid.
The rest of the shudder may well be a wron diff lock. The material on the disks themselves may be wearing off. You will mos tlikely have the old Valeo material ones. I know from personal experience that the newer material units which I have installed in my C4 because my diff locks wore out are quieter and smoother than the old ones. However 90% is better than nothing. I still hope your red warn light is not coming on. Please confirm it is the yellow led.
Ciao,
Adrian
911C4
11-05-2002, 12:56 PM
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FWIW my interlock light + abs + (!) + horn do occasionally lite up.
I checked everything that had to be checked (easy stuff as im not a good mechanic)
However they light up in always the same circumstances ... on the highway doing 120 km or more and whenever there's a little bump due to for example an uneven junction between the road and a bridge ...
This makes me think that there might be a bad connection at a sensor. I suspect the front wheel sensor(s).
The whole thing is reset after restart. It is all very occasionally. I rezally do not worry at the mom.
WSP964
I checked everything that had to be checked (easy stuff as im not a good mechanic)
However they light up in always the same circumstances ... on the highway doing 120 km or more and whenever there's a little bump due to for example an uneven junction between the road and a bridge ...
This makes me think that there might be a bad connection at a sensor. I suspect the front wheel sensor(s).
The whole thing is reset after restart. It is all very occasionally. I rezally do not worry at the mom.
WSP964
11-06-2002, 12:21 AM
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Adrian... it is the yellow LED next to the traction ****. After another day of driving today, I'll adjust my "90%" comment to about 60% improvement. I wonder what my next move should be. It is more evident when traveling at speeds under 45MPH and at high RPM's. Is there anything to the "engagement pressure" idea? The tech was wondering if it either didn't fully engage, or engaged too easily. Just a hunch on his part.
11-06-2002, 05:27 AM
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Okay guys I will answer Wsp964 first.
This problem sounds like one of your accelerometers in the centre tunnel. On the right hand side of the centre tunnel forward of the gear stick there is a little panel held in by 2 screws. Remove these screws and the panel. You will see 2 little black units (plus a relay which is the sunroof relay). Take the connectors off (ignition off by the way) and check for corrosion. Do one at a time. What maybe happening is that the acelerometer is pegging out. This problem normally happens over 100 kph. Quite rare but it has happened before and took us a long time to work it. Sadly this is often an indication of a previous accident and the mounting plate and or the accelerometer are damaged. This will rarely show up as a fault code by the way.
Now to Bobs problem.
Inside each of the diff locks are 18 pressure ports which evenly distribute the pressure. If one or more are blocked you will have an uneven application of pressure and that makes for a lot of grinds and bumps. I would suggest that if one diff lock is partially blocked up both will be if you know what I mean. The diff locks can be removed and repaired but it is often cheaper to replace them. Before doing this you might ask your mechanic to do a bleed of the interlocks system using the hammer. This is a programmed function within the hammer software.
The diff locks can never engage too easily but they can certainly be restricted.
Ciao,
Adrian
911C4
This problem sounds like one of your accelerometers in the centre tunnel. On the right hand side of the centre tunnel forward of the gear stick there is a little panel held in by 2 screws. Remove these screws and the panel. You will see 2 little black units (plus a relay which is the sunroof relay). Take the connectors off (ignition off by the way) and check for corrosion. Do one at a time. What maybe happening is that the acelerometer is pegging out. This problem normally happens over 100 kph. Quite rare but it has happened before and took us a long time to work it. Sadly this is often an indication of a previous accident and the mounting plate and or the accelerometer are damaged. This will rarely show up as a fault code by the way.
Now to Bobs problem.
Inside each of the diff locks are 18 pressure ports which evenly distribute the pressure. If one or more are blocked you will have an uneven application of pressure and that makes for a lot of grinds and bumps. I would suggest that if one diff lock is partially blocked up both will be if you know what I mean. The diff locks can be removed and repaired but it is often cheaper to replace them. Before doing this you might ask your mechanic to do a bleed of the interlocks system using the hammer. This is a programmed function within the hammer software.
The diff locks can never engage too easily but they can certainly be restricted.
Ciao,
Adrian
911C4
