When automotive repairs are more complicated than they should be

Aug. 1, 2018
How hard could it be to figure out a headlight problem on a 15-year-old domestic? Well, we hadn’t tackled one of these S10 headlight issues before, and this one was a wakeup call.

I’ve been in this business since the early seventies, and the guys who are my age and older know that there was a time when the most complicated electrical issue we might encounter on a vehicle would be turn signals or power windows. Even back then things happened that didn’t seem to make sense.  I encountered a ’78 Dodge pickup with an inoperative left-hand turn signal – after checking bulbs, wiring, grounds, etc. I discovered that simply replacing the flasher brought both sides back online.  Never quite understood that one.

Then there was the ’66 Cadillac convertible with a driver side power window issue that would come and go, and as I dug into that one I found a pushed back pin in a connector at the left kick panel – and from the condition of the harness and the connector it appeared that it had been that way since the car was brand new.

Once my brother’s 78 Cadillac developed road-speed radio static that he only noticed after the tires were rotated; back in those days you weren’t supposed to cross-rotate radial tires, and while I was digging in the dash for issues with the antenna and whatnot, he noticed from looking at his spoke rims that the tires had indeed been cross-rotated – and when we put them back like they were supposed to be, the while-driving radio static evaporated.

Then there was the 80 model Lincoln that would buck and skip exactly five minutes after a morning cold start but would never do it again while the car was warm – and that turned out to be a pushed-back wire in the crank sensor connector pigtail. I can’t explain the five-minute deal, but when I seated that connector the problem was gone.

I knew of one six-volt vehicle from the ‘50s that wouldn’t spin and wouldn’t start with the key but would instantly fire up if you put it in gear, pushed it, and popped the clutch. That one turned out to be a bad engine-to-frame ground.

Headlight issue

This little old S10 had a lot of other issues that had been ignored until it developed a headlight issue, and if somebody’s planning to drive at night or in the rain, the headlights are a must-have.  Initially, I was thinking this would be a slam-dunk.  How hard could it be to figure out a headlight problem on a 15-year-old domestic?  Well, we hadn’t tackled one of these S10 headlight issues before, and this one was a wakeup call.

Drawing a headlight job on a truck this old would seem to be a simple exercise.

The initial concern was that the headlights tended to only illuminate on flash-to-pass. Occasionally they would work normally, but usually they wouldn’t. Heck, the Daytime Running Lights wouldn’t even work.  The owner of the truck couldn’t care less about the DRL, which isn’t required in these parts – he just wanted to turn on the light switch and see where he was going at night.

To begin with, I like to see if power and ground are available at the bulbs with the circuit energized, and as we traveled that path, we got side-tracked when we found that we only had ground at the right front headlamp – with the bulbs unplugged, there was no ground at the left front lamp, but with the right front bulb connected, we had a ground. This tended to confuse the student I had doing the work, and so we waded into the wiring schematic – which became even more confusing. Folks who are familiar with this platform are already smiling, I expect.

(click image to enlarge) This schematic is confusing on several levels – note that there are two daytime running lamp relays shown – and one of them parenthetically mentions an RPO code, but the other one simply says “domestic.” The headlight grounds exit the first page going down and enter the next page going up. The ground that passes through the headlight grounding relay begins on the bottom and goes north through the relay and then enters the page in the middle headed south through the Multifunction switch. Complicate that by shoving the grounding relay into a panel ‘way up under the dash and you’ve got a recipe for frustration. Rather than trying to contain all this on one schematic, they should have provided a different one for non-domestic vehicles.This is ridiculous.

One of the maddening things about so many of today’s schematics is how they move from page to page with those funky arrows. Granted, the shop manual folks sometimes give us link boxes on those arrows so we can jump right to the page where the circuit continues, and that’s a good thing.  Gone are the days when the entire vehicle schematic could be found on just one page (of course, that was in the 1960s).  This schematic was light years away from that one-page utopia, and besides all that, it broke some key rules.

I teach my people that, in most cases, on a schematic, power comes in from the top and ground comes up from the bottom of the diagram.  And that’s usually the case, although I’ve seen it violated a few times on isolated schematics for one reason or another. Well, this S10 schematic shatters that rule and inserts some other curve balls in the process.

The origin for the ground was G200, which is under the dash in front of the driver and attached to the bulkhead. That ground feed makes its way through a splice pack to feed a lot of other stuff, but for our purposes, it feeds the headlamp grounding relay through the common and normally closed terminals in that relay. The ground then departs that relay, makes its way to the multifunction switch (from the top of the diagram, no less), and the MF switch feeds it to the headlight bulbs, which are powered by the headlight relay.  As the ground feed departs the MF switch the ground passes through the under-hood fuse block (no fuses in this ground circuit, though) and then exits and splits into four different feeds – all of which exit the page headed south – i.e., toward the bottom of the page – which no ground circuit should be allowed to do (my opinion).  When these grounds reappear feeding the headlamp bulbs, they enter the page from the bottom (as grounds are wont to do).  Since they exit the previous page headed south and enter this page headed north, the student wound up in a tailspin, effectively auguring her troubleshooting plane down into the slough of no understanding.  It was a nasty thing to watch and even nastier to experience, since I was in the copilot’s seat trying to teach her to fly.

Homing in on the target

Understanding the circuit and being able to locate and access the various connector and components is of obvious importance. In this case, the components consisted of the headlight switch, the BCM, the headlight relay, the headlight grounding relay, and the Daytime Running Lamp relay.  The BCM is a major player here, receiving a Headlights OFF signal from the headlamp switch, which, through another part of its ganged array, sends Headlamp Relay Coil power to the BCM so that the BCM can operate the Headlamp Power Relay at its discretion with the switch in the ON position. So, the Headlamp switch, through two different circuits, sends power AND ground to the BCM. 

The BCM is monitoring ambient light by way of an electric eye on the right side of the dash for DRL activation when the other conditions are met.  Both the DRL and the Headlamp grounding relays are feeding the lamps through their normally closed terminals so that when the headlamp power relay is energized, the left headlight is forced to get its ground through the right-hand headlight bulb’s filament – in a word, the headlights are illuminated in series during DRL operation and are only half as bright, rather like the cooling fans that are fed in series when they’re spinning on low. The schematic shows an alternate wiring of the DRL relay if the vehicle isn’t “domestic,” and that doesn’t help a new schematic reader either.

Flash-to-Pass is a separate switch within the MF switch that triggers the BCM to energize both the DRL relay and the Headlamp grounding relay.  The Headlamp Grounding Relay then breaks the circuit to ground and the DRL relay grounds the left headlamp directly, bringing both headlights into a parallel circuit situation for a bright Flash-to-Pass. This is also supposed to happen when the regular headlights are on at night. This wasn’t happening except on Flash-to-Pass, and that was the concern we were pursuing.

Dash-digging and ground-checking, we finally managed to find a bad multifunction switch by checking the ground feed that was supposed to pass through the switch but didn’t.

So we decided to back up and take another run at it. I always teach that circuit checks are best made at the easiest accessible point, no matter where it may be in the circuit, and to work from there. The annoying thing about this truck is that the Headlamp Grounding Relay is in a relay center that is mounted in a very tight spot under the dash on the left hand side, which makes the relay no fun to access. So we began at an easier spot.

Noting that the normally closed Headlamp Grounding Relay contacts feed the ground circuit to the MF switch pin E13 by a yellow wire, we determined that there was indeed a ground at the MF switch but that it wasn’t passing through the switch to the lights.  Ground in – no ground out, not on pins E12 OR E11. That was something of a breakthrough – and when we bypassed the switch, we had lights.  And so I had Kayla replace the Multifunction Switch, the lights worked, and everybody was happy. It was a wild ride, though.            

Transfer case complications

This was a 1997 Tahoe that came in with a rumbling driveline noise, which turned out to be a leaky transfer case that had gone dry and had destroyed itself internally. They had driven the vehicle like this for a while, opting not to do anything about it until the noise became more troubling. The initial complication came from the salvage yard; the first transfer case to arrive was the wrong one.  We had already removed the old transfer case, which was quite a job, since the torsion bars and their crossmember had to be removed and not much of anything had been disassembled on this one for years.  But we made it happen. And when the correct transfer case came in, it looked clean and dry and was the right part, and so we popped it in, put everything back together, and pumped the requisite amount of Dexron II in there. We also replaced the output shaft seal on general principle.  And then came the complication. We drove the vehicle and heard no noise, but when we looked underneath, the replacement transfer case seemed to be leaking the same way the original one had – between the case halves.  So that one will have to come back out for a re-sealing.  I guess we need to devise a method of pressure-testing it before we put it back in there.

This transfer case (top) had lost all its oil and had destroyed itself internally, but the one we got from the salvage yard (which came empty and dry on the outside) started leaking as soon as we drove it after filling it with Dexron II. We don’t charge labor, but in a shop situation, who do you charge for the labor to re-seal it or replace it a second time? This is a dirty deal no matter how you color it.

This one kind of reminds me of a transmission swap we did on a four-wheel-drive Expedition a couple of years back that did famously for about a month and then came back with a cracked flywheel.  It was like having to do the whole job all over again.

On another note, a 1999 F150 came in with a ruined rear end due to failed pinion bearings (it had been driven that way for quite a while) and we snagged a replacement rear axle from the same salvage yard for five Ben Franklins. The brake backing plates were banged up on the salvage yard rear axle, and we had to swap and replace a lot of the brake parts to get the rear disk stoppers done right, but that job went like a song.

The pinion gears in this differential had died and it had been driven enough to mark the carrier pretty heavily. Rather than buying the parts to rebuild this one we just got a replacement. That repair went smoothly.

Ignition quickies – and a complication

There are two of these I’d like to share. One was a 2003 Suzuki XL-7 that came in for an exhaust leak. We found that somebody had started trying to cut the exhaust (to steal the cat, maybe?) but had decided to stop only partway through. After I fired up the torch and coat-hanger welded the exhaust leak shut (we don’t have a wire welder, although we should have, I guess), it became evident that the engine was skipping to beat the band. The driver hadn’t even noticed the skip!  Rather than busting out the scan tool, I grabbed the GTC505 and rested its wand on the top of the coils until I found a high firing voltage on one coil. The plug was new but greasy and we popped a new plug in its place. It took about thirty seconds to locate a bad spark plug and another five minutes to replace it and that skip was history. We also checked the compression on that cylinder and rechecked the spark pattern after replacing the plug, and we cleared the codes with the Autel.

Using this method, we found the Suzuki engine skip (right) within thirty seconds, never having even connected a scan tool. This provides a much higher resolution peek at the ignition system than simply yanking the P030x code and was a LOT faster.

The second ignition quickie was on a 2009 Camry that had developed an engine skip on #1 and had tossed a primary ignition fault code for coil A. The problem was that, while the skip had been dead and present for many a mile, it stopped happening about the time the Camry made it to the shop, which is, as we say, par for the course.

Since the GTC 505 was just lying there in its open box after the other job, I grabbed it to see what the pattern looked like and found that the erstwhile misfiring coil’s pattern didn’t look out of line – of course, the engine was running smooth, too. Nevertheless, I ordered an aftermarket replacement coil from the parts store and installed it, along with a new set of plugs, because this one hadn’t had any and it was only a few miles early according to the maintenance schedule. It still ran smooth, but when I checked the new coil with the 505 I saw an astonishingly high voltage – about 90,000 volts.

I reinstalled the original coil and saw less than 20k, which was what the other three coils were reading. I called the parts store and had them send a different brand of coil, and when we installed that one the pattern was normal.  Then the parts store manager told me that the manufacturer of the first coil had said that Japanese cars require a higher voltage coil and that we had possibly wound up with one of those – not sure what to make of that information, but oh well.

The Camry was an adventure, to be sure – and we never would have known the replacement coil wasn’t right had we not verified the firing pattern after we installed it. Don’t know about that business of Japanese Camry coils needing a hotter spark – but I wasn’t about to let this sleeping dog lie.

The lesson I gleaned from that Camry experience was that it’s wise to double-check after installing the new part – you know, trust but verify? It was a satisfying element of “verifying the repair” that went beyond a simple test drive.  After replacing the coil the first time, the Camry was running so well that I would have had no reason to suspect foul play had I not done an after-check with the 505 just for grins.  Both ignition jobs went a lot smoother and a lot quicker than they would have if we had used only a scan tool.

Then there was the Pontiac Power Loss issue – after we had exhausted scan tool diagnostics on that one, we screwed my homemade pressure test fitting into an upstream O2 sensor hole and found enough backpressure to condemn the cat. We replaced it with a Walker bolt on replacement. It was a fitting end to a satisfying week.

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