I worked at a filling station in the 1970’s and we could handle just about anything a customer wanted done on a car, but on today’s vehicles, a even the simplest jobs can turn into a nightmare.
1998 Ford Taurus
88,365 miles3.0L Engine
AX4N Automatic Transaxle
Wipers, Fuel Gauge, and Power Windows inoperative. Power Steering feels stiff.
Common Links
When we encounter a vehicle with multiple problems that occurred right after a repair, it’s natural to assume that the problems are related to the repair, right? Customers draw that conclusion repeatedly, and the logic seems sound, especially if they can get the shop to absorb the expense. Many years ago, my dad pulled my sister’s ’77 Caprice into his shop and replaced the front brake pads. When she went to pick the car up, the radio wouldn’t work. She had enough savvy to find the fuse and replace it, but it blew right away. Her savvy ended there; she plugged in three more fuses before the guy at the parts house advised her to have the car checked for a short. She and my brother both figured my dad had done something to cause the problem; after all, the radio was working when he pulled the car into his shop. To make peace before things turned nasty, I decided to have a look at the problem. I pulled the radio out and replaced the fuse; it didn’t blow with the harness disconnected. Reconnecting the wires to the radio and touching the metal part of the dash with the unit, I heard the fuse snap. To make a long story short, I found a shorted noise capacitor in the radio, replaced it, and restored the music. It’s obvious, even to a reasonably intelligent but technically challenged person that my dad didn’t short that big capacitor out while he was replacing the front brakes, but simple customer logic dictates that he must have, because it was working before he did the job. Having encountered many such situations in my professional career as a spark-chasing wrench man, I was careful to approach the multiple failure on this Taurus with discretion; I didn’t want to sling mud at anybody, I just wanted surgically repair the concern. The first thing I did was search for common links between the failed components and systems.
Powers and Grounds
The Taurus didn’t have any running problems, just a list of inoperative systems, namely, wipers, windows Variable Assist Power Steering, and fuel gauge. Drawing on this list, I opened the wiring schematic and began my search.
Incidentally, some late ‘90’s Tauruses have a tendency to backfeed a renegade 12 volt signal from the Transmission Range Sensor and fool the GEM into thinking the ignition switch was in the start position. This produces a weird set of circumstances whereby the radio, blower motor, and some other accessories might shut down when the gear selector is moved from one gear to another. If disconnecting the TR sensor restores radio function, simply replace the TR sensor. I had no radio problem.
Looking for common links, I found that on the 1998 Taurus Sedan, the wiper motor ground (G104) is on the left front inner fender near the air cleaner. The Power Window switch ground (G201) is behind the left kick panel. G101 grounds the fuel gauge AND the tank sending unit, and that particular ground is near the battery on the left fender.
And while G104 and G101 are only a few inches from each other, they checked out just fine. One thing I noticed as I let my fingers do the walking through the wire map is that G101 and G201 do have one important thing in common. Both of those grounds feed the Generic Electronic Module (GEM), which is responsible for wiper operation (inoperative), Variable Assist Power Steering, (also inoperative, defaulted to high effort), and the operation of the Accessory Delay relay that feeds the Power Window circuit (which was the first inoperative thing the owner noticed after leaving the filling station). Searching the schematic for common power feeds produced no further results in that direction, but the fact that the inoperative systems (except the fuel gauge) were tied to the GEM intrigued me.
Finding the Accessory Delay Relay, (top right corner of the interior fuse panel) I snatched it and used a jumper wire to bypass it. The Power Windows came alive, but I still didn’t have driver window “One Touch Down” function and the wipers were still as dead as a hammer. The GEM was rapidly approaching the top of my suspect list.
Jumpering these two Accessory Delay relay terminals (yellow arrows - above) in the socket above with the relay removed to see if the power windows come online, I found that they did. On these ISO relays, the three parallel terminals are COMMON and the two COIL terminals. The other terminal is the NORMALLY OPEN terminal, which receives whatever is being fed into the COMMON terminal as soon as the COIL terminals receive power and ground.
Scanning For Data
My tool of choice for most late model Ford scanning is the New Generation Star (NGS) tester. This old Hickok-made T-bone has been out there since the late eighties and Ford had plans to scrap it when the laptop-based Worldwide Diagnostic System came online, but there was such a hue and cry from the field that Ford decided to continue updating the NGS, even providing a card-based interface with the WDS for reprogramming functions. A guy who is accustomed to the NGS will always grab it first when it’s time to scan a Ford. One of these babies costs from $2000 - $3000 depending on whether or not you buy the reflash kit, but it’s well worth the money; the NGS has really nice Generic OBD II capabilities and even contains a banana-plug compatible signal generator output for test purposes.
Plugging the NGS into the Data Link Connector (DLC), I attempted to talk to the GEM module, but to no avail. Running the car through the data link diagnostics test (it sweeps all the busses leading to the DLC), I found that the PCM would communicate just fine, but the GEM communications link (a different wire) was reading “No Response/Not equipped.”
Resisting the urge to throw a black box (the GEM in this case) at the problem, I decided to gather more information. I’ve been burned too many times by assuming a solid state black box was bad only to find that there was a loose connection somewhere else.
A Short Course in GEM-olgy
The GEM module is an interesting little creature Ford introduced on 1995 Windstars, Explorers, and Rangers. The base model Rangers came equipped with a watered down version of the GEM called a “Central Timer Module” (CTM). On these three platforms (Windstar, Explorer, and Ranger), the GEM is stand-alone. The early Windstar module is above the driver’s right shin and on the Ranger/Explorer if you remove the radio and its trim panel, you’ll see it in there on the left.
The GEM/CTM has its wiry little fingers in a lot of pies and handles anything that needs to be timed, and many things that don’t. The wipers get all their marching orders from the GEM module; the stalk switch on the steering column merely interfaces with the GEM, which produces wiper operation by way of a pair or a trio of relays in the PowerDistributionCenter under the hood, depending on the application. The GEM also handles all the chime functions the One Touch Down driver side power window, and some of the instrument cluster warning lamps.Another GEM-driven responsibility is to time out the Battery Saver relay, which shuts down battery-killing interior lights 45 minutes or so after the vehicle is parked and, on the 98/up platforms, when vehicle speed surpasses 5 mph. GEM also handles the Accessory Delay function, which allows the driver to listen to the radio and operate the power windows for a given amount of time or until a door is opened, whichever comes first. The GEM on some vehicles will even sound a warning chime if the vehicle is driven ½ a mile with the turn signal engaged! The GEM not really a body computer per se, but it’s close. Taurus received its own GEM in 1996, the F-Series pickup, and the Expedition got one in 1997, both of these riding piggy back on the interior fuse panel/junction box. Crown Vickies and some Lincolns have a “Lighting Control Module” (LCM) which is a different animal.
Let’s digress here for a moment to discuss a newer development: Windstar got two separate GEM devices in 1999, one to control the electrical system on the front end of the van and the other to control the rear. The two modules communicate with each other to keep things going smoothly. The fuel sender on this Windstar filters its signal through the REM instead of being hard wired to the gauge the way it once was.
Information Transfer
Listen up, now, this is important! On Explorers and Rangers, beginning in 1998, the Ranger/Explorer GEM must be configured with the rear axle data and tire size when it is replaced or the speedometer won’t work right and the automatic transmission won’t shift. This operation is performed by using the NGS to temporarily store the data until the module is replaced; this is the best way, but if the original GEM was totally fried, the information can be selected and programmed into the new module. The aggravating old shift-on-the-fly module Ford used for all those years on 4WD applications has been pre-empted by this nifty little GEM, which, unlike the old module, communicates with our scan tools quite nicely.
Isolating the Problem
Printing the connector pinouts and the schematic for the three accessible GEM module connectors, I found that all the fuses feeding the GEM were all good and that powers and grounds were present every where they were supposed to be. Furthermore, as far as the communication problem goes, the blue-white Data Link Connector bus wire had good continuity all the way from the GEM connector to the DLC.
The remaining inaccessible GEM module connector is a direct plug-in to the rear of the interior fuse panel/junction box, and I have seen numerous Expeditions and F-series pickups with junction box problems, but never a Taurus. As I continued to consider the big picture, it became clearer: The Power Windows wouldn’t work because the GEM couldn’t energize the Accessory Delay Relay, which is always energized when the key is on. The Wipers wouldn’t work because they depended on the GEM to fire up their relays.
The DLC above provides scan tool access to the GEM’s innards via this terminal (yellow arrow), which is connected to the business end of a blue/white ISO protocol wire over which the GEM communicates.
Here are the accessible GEM module connectors (left). After disconnecting them I found power and ground feeds in the proper cavities. The GEM was toast.
GEM Module Connectors (above) and piggyback connector that plugs into the fuse panel/junction box (below).
The Data Link communication problem appeared to be yet another symptom of a GEM module that had either died of natural causes or had been murdered, but there was yet another mystery: The fuel gauge was totally separate and apart from the GEM module and it was on the blink as well.
Concerns Pinpointed
The fuel gauge was reading past full the way these gauges do when the sender is open or unplugged. I always like to go to the tank connector (front right side of the tank) and ground the yellow-white wire to see if the gauge will drop to empty. If it does, the sender is at fault. In this case, grounding the sender did nothing. Reconnecting the tank sender and moving to the point where the yellow-white sender wire passes through connector C214 en route to the instrument cluster, I checked the wire for continuity through the sender (a high impedance test light works well for this) and found a gentle path to ground through the tank sender. Removing the cluster revealed a scorched transistor on the slosh module circuit board (bottom right of photo).
This little signal filter is plugged into the back of the instrument cluster on Fords with non-electronic clusters; it keeps the fuel gauge from reacting to sloshing gasoline, but in this case, it had opened the circuit feeding the gauge, thus causing the gauge to read as if the sender were unplugged. The slosh module for this car comes only with a new gauge.
A new GEM module brought the wipers and windows to life, as well as normalizing the power steering, and the DLC had good communication.
In retrospect, it appears that somebody connected a pair of jumper cables or the new battery backwards and fried these two solid state parts. Since we don’t charge labor at the college, the bill for the repairs slightly below $200. It could have been a lot worse. R.W.M
Learning From My Experience 
