Don't forsake the vehicle manual

Jan. 1, 2020
Now I'll grant the fact that some shop manuals, even the factory ones, aren't laid out well, and finding the simplest information can be an extremely annoying egg hunt. Technical service bulletins (TSBs) and recall archives go beyond shop manuals and

Opening the book is important, whether you're fixing turn signals or timing chains.

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I've been running my automotive department like a shop for the past 10 years. Customers are only slightly less demanding than they are at a shop, and I try to match the pace of the work in my classroom shop to the way things are done in real world service bays. An oil change shouldn't take more than 30 minutes. A correctly done brake job should be done within a couple of hours. A student should be able to handle a cylinder head R&R within the space of a day. Does it always turn out that way? No. But then, no two jobs are alike.

Before the first job I held as a dealership technician, the only things I looked up in shop manuals were those screwball firing orders on Cadillacs, ignition timing and torque specs on heads, rods and main bearings. Carburetors came with their own instruction sheets, breaker point dwell and/or gap was committed to memory, and just about every engine took five quarts of oil. Today's vehicles are impossible to fix without information; Alldata, Identifix and Mitchell on Demand are the resources most independent shops depend on. Hyundai makes its factory shop manual information available for free (at least at the time of this writing), but it sometimes takes serious leg work to sort things out.

I first parked my toolbox in a dealership service department in 1983, but I had been wrenching for a living for almost a decade at that juncture: first with my dad, then at a gas station, then doing fleet maintenance work in Southeast Texas. What I discovered at the VW/Mazda dealership was something that redefined my life as a technician from that point on: wiring diagrams. The crisply drawn maps of how those cars were wired became a new and wonderful tool for me, and nobody had to teach me how to read them. It seemed as if everything I had always wanted to know about vehicle electrical systems suddenly opened up right before my eyes.

Let's face it, anybody who tries to tackle a wiring problem without a schematic can get in serious trouble if they don't have prior knowledge of how a particular vehicle is wired.

Shop manuals are an essential tool none of us can do without, and it never ceases to amaze me how some of my students – particularly the ones who are kind of wrench smart – seem to believe they can plow into a complex job and figure it out as they go instead of gathering pertinent instructions from the shop manual. Heck, I won't even pull a door panel on an unfamiliar platform without at least looking at the shop manual illustrations. Now I'll grant the fact that some shop manuals, even the factory ones, aren't laid out well, and finding the simplest information can be an extremely annoying egg hunt. Alldata has done a lot to standardize the information they have available, but no single source has everything you need on every vehicle. Technical service bulletins (TSBs) and recall archives go beyond shop manuals and are priceless when it comes to surgical repair of an easily defined concern. Then there are those things we need to know that aren't in the shop manual. Experiences by others in the field are just as priceless; that's where iATN and Identfix come in handy. Here's a seemingly simple turn signal problem that would smack a book-dodger out of the park.

It Really Seemed Simple - NOT

Michele is a college student who brought her 2000 Grand Cherokee to the automotive department for an oil change. One of the guys I had doing the work noticed that the passenger side front turn signal wasn't working. She knew about it, but never decided to have anything done about it. My guys went after that turn signal problem. How hard could it be?

One student, Derrick, removed the headlight assembly to gain access to the bulb. The newer style plug-in bulbs can look good (no broken filaments) and be bad. Those tiny wires on the base of the bulb don't have a lot of contact area, and sometimes they tend to oxidize, build resistance and stop carrying current. Derrick replaced the bulb, but the turn signal was still dark.

Next came the test light. There was no blinking power at that socket (not with the hazards or the turn signals), but the rear signal on that same side was doing the tattletale rapid cycle blink we've all seen over the past 20 years. That calculated decision is made by the electronic flasher unit most vehicles use nowadays and obviously is written into the flasher's chip to warn the driver that there is a problem. This kind of flasher usually has three pins, but it can have five pins in the standard ISO relay pattern and look almost exactly like a conventional ISO relay. The body of that flasher is larger so as to prevent its insertion into a simple relay socket. These units are smart enough to measure current and then change the cycle time of the working elements on that side of the vehicle.

Fact Finding

Most of us older guys remember those thrilling days when the turn signal switch received power at key on and routed that power through the old round two-pin turn signal flasher when a turn signal was selected. The brake lights were wired through the turn signal switch, too, so that when the brakes were applied, the stop lamp on the appropriate side would flash. On those, if you had inoperative turn signals but the lights came on when you bypassed the flasher, you knew the flasher was bad. It was pretty simple. Then came electronic flashers, lighting control modules, BCMs, REMs and GEMs, etc.

We dug into the shop manual and wiring schematic. This Grand Cherokee's turn signal flasher is in the junction box (left of steering column). You can barely touch the flasher with your middle finger. The knee bolster has to be removed for access to the two fasteners that secure the junction box. With those fasteners removed, the junction box can be moved back enough to access and replace the flasher.

It's the tallest relay in that box and it's in the center of a row of shorter relays. This flasher has nine pins: two power pins (one B+ and one Hot in Run), three sense wires (Left and Right Turn and Hazard) and four outputs (Right Front Turn feed, Left Front Turn feed, Right Rear Turn feed, Left Rear Turn feed). Like the ancient two-pin round flasher, this one has no direct ground connection except through the bulb filaments when the switches are at rest.

The feed to the right front turn signal assembly makes its way from flasher pin 3 out through the innards of the junction box through the C2 connector (pin 26), where it travels through pin 54 of C106 and pin 3 of C112, thereafter making its way to a splice, feeding the side marker lamp and the turn signal bulb on that side.

With this configuration, a single turn signal bulb can fail due to a bad flasher. After tracing the current through a couple of connectors, the wiring schematic led us to the flasher itself. Tugging on the flasher with one finger, I could get the turn signal to work, but it wouldn't work consistently. Removing my finger pressure from the flasher would render the turn signal inoperative once more.

Fault Finding

Was this a junction box internal connection? I had no way of knowing; the pins looked tight. It was time for an A-B-A swap. I had an A flasher in my hand, but no B with which to swap it, so I borrowed a flasher ($69) from the local parts supplier (he likes me) and plugged it in to be rewarded with a consistently dependable right front turn signal. It would have been particularly revolting to buy a flasher only to find that the junction box was at fault, and I wasn't about to go there if I could help it.

I appreciated the loan of a good part, but when I found that I could buy a flasher from the local Jeep dealer for a mere $40, the parts store flasher was returned with an explanation of exactly why. The parts store couldn't match the Chrysler place's price; its supplier was charging it more for the unit than the dealer was charging me. My good-natured parts guy sells me a lot of other stuff, so he took the flasher back without complaining.

Now, imagine having to repair the turn signal problem on this vehicle without a schematic? Potential causes for this same concern abound, from bad wiring connections to a bad turn signal switch, to a bad junction box and so on. Would a shotgunner replace the flasher before replacing the switch? Probably not, because the right rear turn signal was operative. This smacked of a wiring concern before we did our homework and found the bad flasher. The whole thing was both fun and instructive on several levels.

The Altima

Now comes the embarrassingly dumb mistake we made by thinking we know certain things so well we didn't need the book. It happened to us on a 2003 Altima. This 4 cylinder was ingesting water from the cooling system jacket via a breach in the cylinder head gasket, which is a fairly ordinary problem for these cars. We had replaced the cam and crank sensors on this car a year or so ago with the recall parts.

But as for the head, we saw no evident warpage on it or the block and no cracks anywhere, and everything went according to Hoyle. Even though this was a high mileage car, we opted to try and use the old timing components because they looked fine (that was dumb, I know). Well, with the colored links and the "obvious" marks all lined up (like idiots, we never consulted the shop manual to verify what seemed obvious), we found that the Altima wouldn't start – it had no spark.

The shop foreman at the Nissan dealer (he's one of my graduates) mentioned timing chain stretch as a significant factor in causing the cam/crank signals to be out of sync. Well the car was running when it came in, but we acquired a new timing set and measured it against the old chain. Sure enough, it was stretched, but we still had a no-start. Then we found out when we looked at the book that we had used the wrong timing mark on the intake camshaft. We were burned by our own failure to check the book.

We did manage to remove the upper cover, use the balancer timing mark and the lobe positions to put it back in time. It was tricky, but we were motivated and everything turned out just fine.

It was largely my own fault, because I thought we were using the right mark too and it wasn't until things had gone sour that we went to the book and found our mistake. Why that mark is on the intake gear will always be a mystery to me. It looked like a legit timing mark, and we fell for it. It was one of those DUH moments.

I guess I'll conclude with a personal quip: Forsake the book at your own peril – information is the lifeblood of this industry.

Richard McCuistian is an ASE-certified Master Auto Technician and was a professional mechanic for more than 25 years. Richard is an auto mechanics instructor at LBW Community College/MacArthur Campus in Opp, Ala. Email him at [email protected].

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