Hello All,
I'm a long time reader, first time poster. I have the infamous blinking 4x4 light.

I changed the oil a couple of weeks ago and when I started it up the 4x4 light started flashing. The filter is located on the block and I immediately searched around that are to be sure I did not move anything. I did not find any wires that I could have moved. I then search this forum for an answer.

What I found was that it could be one of the two sensors that are either in front or rear of the transfer case. Using my digital ohm meter I checked for continuity between the 3 wires that come out of each sensor. I could find continuity between a couple of wires (do not remember if all 3) from the front sensor and I could not find continuity between any wires from the rear sensor. I went to all the local parts stores (Autozone, Checkers, etc) and none had either of the sensors. They did have a speed sensor that looks like its gear driven- Wells # SU2121 which was not what I need. My sensors are hall effect and look like a little "shoe" with a white "thread".

I had to special order the rear sensor from the Ford dealer. The part number is :SW-5586 YL1Z-7F293-AA. It's called a "rear case sensor- output". I also purchased the front sensor just in case I need it in the future. The front sensor part number is: SW-5644 1L2Z-7F293-BA.

I replaced the rear sensor by taking each wire from the connector, one by one, and inserting the new wire into the connector. All the wire colors were the same as the original. I disconnected the battery for around 5-10minutes and restarted the engine. The 4x4 light kept blinking. I checked the connector again and everything looked fine. Since I had the new front sensor in the box, I tried to check the continuity between all 3 wires using my digital ohm meter. I could not find continuity on the new sensor. Why could this be? Does it have to be installed in order to check for continuity?

Can I have the same problem with the new rear sensor as well? I did not check the rear when I installed it.

Please send me suggestions for solving this problem. 4x4 high and low work when the switch is turned. The AWD worked perfectly until the oil change which has nothing to do with the problem, or does it?

Thanks,
zmanmike

99 Expedition, 5.4L, Full-time AWD

 

Anyone? BTT.

 

Mike, it could be many things. Here's the info I dug up from my manual:

PINPOINT TEST A: THE 4X4 INDICATOR FLASHES WHEN THE A4WD MODE IS SELECTED — 4X4 INDICATOR

Note:
The vehicle has to be driven in A4WD 30 mph or greater and/or encounter a slip condition before the 4x4 lamp will flash for certain faults.

Note:
Complete the entire pinpoint test related to the symptom before replacing the GEM.
A1: CHECK THE IGNITION STATES
A2: RETRIEVE THE RECORDED GEM DTCS FROM BOTH CONTINUOUS AND ON-DEMAND SELF-TESTS
A3: CHECK THE 4WABS MODULE INPUT; 4WABS MODULE CONNECTED — MONITOR THE GEM PID PWR_RLY
A4: CHECK THE 4WABS MODULE INPUT; 4WABS MODULE DISCONNECTED — MONITOR THE GEM PID PWR_RLY
A5: CHECK CIRCUIT 239 (WH/OG) FOR SHORT TO POWER
A6: CHECK HALL EFFECT POWER CIRCUIT FOR SHORT TO GROUND — MONITOR THE GEM PID HALLPWR
A7: CHECK THE HALL EFFECT CIRCUIT FOR SHORT TO GROUND — TRANSFER CASE ASSEMBLY C1019 DISCONNECTED
A8: CHECK FRONT AND REAR HALL EFFECT SENSORS
A9: CHECK CIRCUIT 774 (LG) FOR SHORT TO GROUND
A10: MONITOR THE FRONT AND REAR HALL EFFECT GEM PIDS TRA_RSP AND TRA_FSP
A11: CHECK THE VOLTAGE TO THE HALL EFFECT SENSORS — CIRCUIT 774 (LG)
A12: CHECK CIRCUIT 774 (LG) FOR OPEN
A13: CHECK CIRCUIT 682 (DB) FOR OPEN
A14: CHECK THE VOLTAGE TO THE HALL EFFECT SENSORS — CIRCUIT 774 (LG)
A15: CHECK THE HALL EFFECT SENSOR GROUND CIRCUITS 682 (DB) FOR OPEN
A16: CHECK CIRCUIT 435 (YE/LB)/722 (LB) FOR OPEN
A17: CHECK CIRCUIT 435 (YE/LB)/772 (LB) FOR SHORT TO GROUND
A18: CHECK CIRCUIT 435 (YE/LB)/772 (LB) FOR SHORT TO POWER
A19: MONITOR THE TOD RELAY GEM PID 4WDCLST
A20: CHECK CIRCUIT 976 (OG) FOR SHORT TO POWER
A21: CHECK CIRCUIT 976 (OG) FOR SHORT TO GROUND
A22: CHECK CIRCUIT 976 (OG) FOR OPEN
A23: MONITOR THE GEM PID 4WDCLST — REAR WHEELS BREAKING TRACTION
A24: MONITOR THE GEM PID 4WDCLST FOR ON--- RESPONSE
A25: CHECK CIRCUIT 976 (OG) FOR SHORT TO POWER
A26: CHECK THE A4WD OUTPUT
A27: CHECK CIRCUIT 779 (BR) FOR OPEN
A28: CHECK CIRCUIT 779 (BR) FOR SHORT TO GROUND
A29: CHECK CIRCUIT 779 (BR) FOR SHORT TO POWER
A30: CHECK TOD RELAY CIRCUIT 57 (BK) FOR OPEN
A31: CHECK THE VOLTAGE TO THE TOD RELAY — CIRCUIT 704 (DG/LG)
A32: CHECK THE VOLTAGE TO THE TOD RELAY — CIRCUIT 294 (WH/LB)

You might want to take it in and have it diagnosed.

Good Luck.

 

This problem sounds very familiar, although I only had a brief period where I got my 4X4 light to flash.

When I hit about 30-40,000 miles, I started to get a shudder when I was making tight turns at low speeds. Since it acted like it was in 4WD, I started digging into the problem and ended up ordering the same two hall effect sensors. The dealer told me that he has heard of cases where metal shavings collect on one or both of the sensors (they have magnetic properties), and this causes the speed sensors to read incorrectly. If the speed difference exceeds a certain amount, it kicks in the 4WD system.

I went ahead and replaced the two sensors (one of which was covered with iron filings), and the problem got much worse. I also found that my 4X4 light started blinking after the problem occured. Once my light started blinking, it apparently "kicked out" the AWD system and my problems went away until the next time I started the truck.

It turns out that I did not have one of them tapped in far enough (they were a tight fit), so it apparently wasn't reading anything at all. Naturally it was the one tucked up behind the actuator motor, so I was cursing quite a bit. Anyway, the condition improved for a little while, but I still get into the problem on a fairly regular basis.

I have basically learned to ignore the problem, but I would go ahead and replace the sensors for a 2nd time if I thought it would make the problem go away entirely. From where I sit right now, I am hesitant to replace the sensors again because the problem was definitely worse when the sensor was improperly installed (it actually caused my 4WD system to shut down entirely when the sensor was out of range).

I would not expect to see such a difference between "bad sensor" and "out of range sensor," because this is just the mechanism for the truck to automatically go into 4WD without me activating the selector switch. Using this line of logic, the problem at its worst should be no different than if I had manually selected 4WD Hi on my dashboard switch. While the ultimate results are similar, I have never found that running 4WD on dry pavement generates enough vehicular stress to cause a complete shutdown of the 4WD system.

If anyone has an insights into this, please let me know.

Jerm

 

Hello All,

I FIXED the 4x4 blinking light this past weekend! I went ahead and replaced the front sensor since I had already purchased it. It was a pain to get the new one flush with the transfer case body (I dabbed a little bit of oil on the o-ring). When I started the truck up, no more blinking light.

I have a couple of observations to share though:

1) The front sensor did have crud (mixture of metal shavings and stuff) on the "shoe" part of the sensor. When I measured the resistance it showed as 'good', but I decided to replace since I had the new one already. Might still work after I cleaned it with brake cleaner. If I ever have a problem again I'll put it in to see if it works.

2) If you read my initial post, when I tried to measure the resistance of the old rear sensor (which I replaced first) and the resistance of the new front sensor, my digital ohm meter showed they were both "open." I could not believe that a new factory part (or two since my problem did not away when I replaced the rear sensor) could be bad. So I reversed the ohm meter leads when I measured for resistance on the new front sensor, and guess what?, it was good. I tried this on the old rear sensor, and it was good too. There must be some sort of diode or something that would not allow the ohm meter to read one way, but read perfectly fine on the other.

In case someone is wondering how much these things cost. I paid approx. $48 for the front sensor and had to special order the rear for $55. The only difference that I could see was that the rear had longer leads.

Well I hope this information helps some one in the future.

Thanks,
zmanmike

 

Great post, solved some of my problems so far. I just swapped out the transfer case motor since the 4x4 hasnt worked in over a year. Now, when I start the truck and drive away the fronts lock up (I guess that's a good sign, and it feels pretty rotten on dry pavement). When I take a couple of turns and a couple of stops the 4x4 light starts to blink, and the AWD turns off (only rears are turning now). Now, when I manually put it in 4wd from the switch, nothing happens, no light, not even a blinking 4x4 light. When I flip it back to AWD, the 4x4 light blinks again. Can those sensors prevent me from putting my truck into 4x4 manually?

Mike

99 Expy 5.4

 

My 4x4 dash light has been blinking for a while now, i've been reluctantly ignoring it, i've recently decided to fix it or i'm going to be in trouble. there hasn't been any other indication of a problem, no shaking, no problems with switching into or out of 4 wheel drive etc. it's just annoying me. i've called the dealership asking about these speed sensors i've just read about and they tell me there are no speed sensors on the front transfer case, so i gave them the part numbers i got from the post with the 5.4l (mine's the 4.8 w/ a 4R-70 transmission) so, the part numbers don't match up. they finally gave me a part number for the transmission range sensor, which i replaced a year ago trying to eliminate the randomly won't-start issue. could someone find or does one of you know the part numbers for these sensors that i need, seeing as the dealership is rather incompetent? thanks,
Kris

 

when you check the sensor with the ohm meter, are you just checking for continuity, or for resistance? And if it is resistance what should it read. thanks

 

Did anyone ever take the sensors out and clean them?