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Learning from bad judgement in auto diagnostics

Tuesday, January 1, 2019 - 08:00
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We usually do our best and most efficient work on vehicles with which we’re familiar, but there are times when even the ones we know the best can smack us around – particularly if we make the wrong choices. But in the midst of troubleshooting and repair, we usually learn the most from our errors. An old cowboy proverb I read years ago can be paraphrased by the statement that we usually learn good judgment after having experienced the negative results of bad judgment. In the world of automotive electronics, that good judgment learning curve can be deep and steep, even if we’ve already fixed a multitude of vehicles, and I’ve been in this business for more than 40 years now.

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The F-150 and the not-so-perfect storm

A 2003 four-wheel drive F-150 5.4L with 213,654 miles was one of those bad-judgment learning curves. Sometimes trying to save a customer some money costs us a heck of a lot of work. This was a windshield wiper concern. How hard could it be? Somebody had already replaced the multi-function switch, too.

This 2003 F150 is in pretty good shape, but you don’t need to drive in the rain without wipers and so here it is.

For the last 20-plus years on these F-150s, the wiper system has its switch (part of the multifunction switch) wired to a dedicated control circuit in the Generic Electronic Module (GEM), and three relays in the underhood fuse box; one for low speed, one for high speed and a third relay for the washer motor. The algorithms in the GEM module software are supposed provide the relays with their marching orders based on the chosen switch position.

The wiper switch portion of the GEM module’s IDS datastream screen is a long tracking bar that has failure areas on each end and normal switch positions in the middle. As we cycled the switch through its positions, the IDS put shadow tracks in all the right places and none of the wrong ones, indicating that the GEM was reading crisp, accurate commands. So far, so good, but still no wipers.

When this first wiper module didn’t work right (top), I had the salvage yard snag me another module – which turned out to be a problem because Hurricane Michael heavily damaged the yard’s Panama City warehouse and replacement module was still on the truck inside the warehouse.

I was able to turn the wipers on by telling the IDS to activate the wiper relay, and when I then activated the speed relay, the wipers would go into high gear. When I turned the wiper relay off, the wipers would park. I could select the washer pump relay and the pump would wet the windshield with its spray.

Removing the steering column shrouds, we found the square connector crumbling, so we bought a replacement pigtail and put it in place with solder and heat shrink to no avail – the wipers still didn’t work. As an experiment, we had the parts store send a new switch, because these switches look exactly alike from year to year but are different internally – I found that out the hard way when I was at the dealer. From previous experience I discovered that a ’98 switch won’t work on a ’99 model, and so on. You must use the right switch. Period. The new switch changed nothing, so we sent it back.

So why wouldn’t the GEM activate the relays when commanded by the switch if the IDS indicated that it was receiving (and reporting) the switch commands? This had to be a problem within the GEM module, and I usually get black boxes from the salvage yard when I can, sometimes because replacement modules aren’t available at the dealer and sometimes because the replacements are so expensive. So, I gave the salvage yard the number that was on the old module’s sticker and bought a $65 used module that was supposed be the right one. The sticker on the replacement did say it was for a 4-wheel drive F-150, but it didn’t have the same prefix and suffix numbers as the original module.

We used the IDS “Programmable Module Installation” feature to save the existing module’s data in the Toughbook, and then we installed the replacement module (which rides piggyback on the fuse panel in true Ford style) and did the requisite data dump into it from the IDS. Well, we got an error message. Was this even doable with a used module? I wasn’t sure. We were in discovery mode. With the used replacement module in play, you could turn the wipers on first low and then high and they would work, but when you turned the wipers off, they would remain on high, and sometimes the washer would randomly start spraying.

I had installed new/rebuilt GEM modules like this, but this was the first time I have ever tried to install a used GEM module like this. Was it a bad idea? It was beginning to look that way.

At this juncture it was evident that this module obviously wasn’t going to work for us on this job, but it did let us know we were moving in the right direction. The salvage yard said that there was another module at their warehouse that did have the right prefix and suffix numbers, but we ran into a hiatus on that one because Michael the hurricane washed that warehouse away the next day, so we had to wait for the next GEM module. But when it arrived and we did the Programmable Module Installation again, we got a different error message and different errors. This time, the wipers worked almost perfectly but the power windows didn’t because the GEM module wouldn’t turn on the accessory delay relay. We had wipers but no windows. We So we were back to square one. The discovery was that, in this case, it would have been smarter to begin with a refurbished module from the Ford dealer.          

A ’96 Jeep Grand Cherokee

This Jeep wasn’t a discovery and judgment case, but it bears mention. It came to us with a non-functional A/C system and no compressor operation. This was The Neutronics identifier showed us nothing but air in the system, and so we ran a 15-minute vacuum, didn’t see appreciable vacuum decay, and went on to shove the requisite amount of cold stuff into the piping. The A/C worked at this point, but we knew there was a leak somewhere, else it wouldn’t have been empty to start with.

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