Hey everyone,
I have a problem with my 93 Aerostar, 4.0L, AWD. The AWD light is flashing twice (code 2 I guess), and when I make a tight right hand turn I get a repetitious clunk (sounds like it's coming from the t-case area). The clunk came first, and when that happened the AWD light started flashing, so they're related to one another. Also, when I park and turn it off, the van shudders/clunks slightly and rolls back a touch, like something in the driveline is settling into place.

I'm leaning towards something mechanically wrong due to the clunking, rather than the electronics as the cause, but does anyone have any ideas? I checked the speed sensors on the t-case, and they weren't covered with any metal filings (they're both pretty worn though), but I did notice something odd. The connectors had a small amount of tranny fluid in them. The areas around the sensors are dry as a bone, and the rubber boots were on the connectors. Is it possible that the sensors are cracked and the fluid came from the t-case, went through the sensor, and into the connector?

Anyone know what the code means? Any help would be most appreciated. Thanks!

 

I would clean the electrical connectors with electrical contact spray and then coat inside with silicone dielectric grease.
The AWD code 2 is signaling that there the "clutch connector or clutch coil has discontinuity".

see>
http://home.comcast.net/~classical_man/wsb/html/view.cgi-photo.html--SiteID-2341390.html
for picture of the module harness connector

1. disconnect the cluch harness connector from the clutch line on the transfer case housing.
2. turn the ign. sw. on
3. shake the clutch harness and check for battery voltage between the clutch connector + pin and chassis.

Is voltage present (steady or intermittent)?

Yes
REPAIR short to B+ on the clutch circuit or REPLACE control module.

No>

Pinpoint Tests

PINPOINT TEST FF: E4WD CLUTCH

FF2 CHECK FOR SHORT-TO-GROUND ON CLUTCH CIRCUIT

l Turn the ignition switch OFF.

l Disconnect the module harness connector from the module.

l Set the ohmmeter to the 20 ohm scale.

l Shake the module harness connector and check the resistance between MHC pin 14 and chassis ground.


l Is resistance intermittent or below 1 ohm?
Yes
REPAIR short-to-ground on the clutch circuit. REFER to the Wiring Diagrams in this section.
No>
Pinpoint Tests

PINPOINT TEST FF: E4WD CLUTCH

FF3 CHECK FOR AN OPEN ON THE CLUTCH CIRCUIT

l Turn the ignition switch OFF.

l Disconnect the module harness connector from the module.

l Set the ohmmeter to the 20 ohm scale.

l Shake the module harness connector and check the resistance between MHC pin 14 and pin 13.


l Is resistance between 1.5 and 4 ohms?
Yes
see below>CHECK CLUTCH BY POWERING CIRCUIT
No
REPAIR open in clutch circuit or REPLACE clutch.


PINPOINT TEST FF: E4WD CLUTCH

CHECK CLUTCH BY POWERING CIRCUIT

l Disconnect the module harness connector from the module.

l Connect Clutch Coil Locking Tool D91T-50-CLT or equivalent to the MHC. If tool is not available, ground MHC pin 13 to ground.

l Jumper MHC pin 8 to MHC pin 14.

l Verify clutch engagement by test driving vehicle in tight turns and noticing driveline wind-up (driveline wind-up is noticed through steering wheel feedback or wheel hop).


l Does clutch engage (driveline wind-up)?
Yes
REPLACE the control module.
No
REPLACE clutch or look for a mechanical failure in the system.

 

Thanks a lot!! The first test you mentioned narrowed it down to the control module. I'm glad i found out the problem without too much difficulty, but I'm not real pleased to find out it's a $290 part. That's just insane. Looks like I'll be making a trip to the junkyard tomarrow. Thanks again!!

 

My '96 4WD ran fine for a year with the module disconnected with no adverse reaction. Unplug it under the drivers seat and see if it works better.

 

Just another thought is to check the status of how well the front dif is connected to the frame. It is a semi common problem for them to crack, break, or twist, especially when you have issues with the transfer case.

 

Thanks for the tips. I already unplugged the module, and all the problems have gone away, so now I just need to find one (I refuse to spend $290 for one).

Does anyone have a schematic for the module? I started ringing out the board inside in hopes of fixing it, but a schematic would be a lot of help. Thanks.

 

Before you blame the module, check out the resistances between the pins of the speed sensors. There are 3 pins on each sensor, and the resistances should be about 1000, 2000, and 3000 ohms between the three permutations.

 

I would also clean the speed sensor on the rear axle. If it gets dirty on the inside it will send false speed to the module.

 

Before you go to ford check out 'give a little thread' I have 2 of them sitting here.

 

That's very generous of you. Could you tell me what part numbers are on the modules you have? Calling around to different yards, I found out there's two different models. Thanks!

 

I will post the numbers tomorrow, I was working out there untill the mosquito's chased me inside, theres nothing like giving blood in the evening

 

Ok the one from the 92 has this number
F09A-7E453-AE
A1611O09
and on the black plastic *70547*
The other from a breakers yard I can't remember to year
F19A-7E453-AA
0974O09AG
*141059*
I havn't checked the other 2 vans, but I have a feeling they may be all different, I'm sure everyone will be checking there's in the next few days aswell. Personally If mine goes I'm just putting the switch in so I can manually flick the AWD on, this is what I have done in my 91 due to the front clutch something or other. Only need it after November till May and then it stays off.

 

Well, I hope you're not leaving it switched on from November till May. The van's AWD is always operating, the control unit just runs a lock-up clutch as a get-unstuck feature. If you leave it locked, it's akin to driving an F-150 4x4 down the road with the hubs locked in and the transfer case in 4HI all the time. Bad news...

 

No thats exactly what I do, if I need it I have the AWD in for 90% of the time it's off and just has partial transfer to the front. Honestly I ran it for a year with suspision that there was no AWD before I investigated it further. Never got stuck but could have been better, last year when it was looking a little sketchey I flicked the switch and felt much more confidence, a lot of it has to do with the way you drive, to many SUV owners think it's jsut the same as driving in the summer with 4WD. I only noticed as it snaked when pulling out the driveway, the rest of the time I jsut drove within the limits of any van.

 

The way the AWD system is designed, the AWD is always active. Inside the transfer case, there is a center differential that splits torque 1/3 to the front and 2/3's to the rear always. It is never in a RWD-only mode. The differential allows the difference in front to rear axle speeds just like a diff in an axle allows side to side wheel speeds in a turn. Because power is routed through a differential, it has no choice but to be always going to both axles.

Now, there is also a clutch inside the transfer case. This is there to lock up the differential if you loose traction on one end or the other. This clutch is what the module under the seat controls. When it is unhooked, the get-unstuck ability of the clutch is rendered inoperable, but the underlying center differential is still sending torque to both axles. There's just nothing to prevent wheelspin if one wheel gets on ice...

If you leave the clutch switched on, then the clutch is locked 100% of the time, at least when it isn't being forced to slip. Again, on dry roads, this can lead to same issues as running a 4x4 truck in 4HI - fatigue in the driveline and accelerated tire wear. In the case of the Aerostar, it can also lead to damage to the clutch or the center differential. So, obviously, this course of action is not advisable...