Disguised diagnostics: When one automotive issue cloaks another

March 1, 2017
One serious problem cloaks another one to the point that the first fix isn’t the final one — and some customers are more understanding than others.

Those of us who have attended manufacturer schools know full well how important the progression of a repair goes. First, the concern must be verified (if possible). The freeze frame data helps in that regard with drivability problems, because that snapshot provides what Chrysler used to call a “similar conditions window.” But then there are those problems a scan tool can’t detect, but our ears and eyeballs can. Spraying or dripping fluid leaks. Engine noises from inside and outside; whining alternators and power steering pumps; rattling or rumbling A/C compressors. Those are easy to verify, but some of them can be difficult to pinpoint.

Back in 1977 I was working at a small independent shop for a guy named Ed Davis. That shop had a concrete floor, but no lifts, and it looked like a big barn, but it was in a good location. One day a ’70 model Ford pickup came driving in the door, and it sounded for all the world like something major in the engine was about to come undone. I stood there thinking we had a major overhaul on our hands, but Ed had the owner switch the engine off, and then he took his pocketknife and cut both belts off. I noticed that one of the belts was gapped and had chunks missing, but so what? That noise was nasty – surely there was metal on metal hammering somewhere! But when the owner restarted the truck without the belts, it sounded so smooth and quiet that I absolutely couldn’t believe my ears. A new set of belts fixed that one. Since then, I’ve been smacked around a few times by one problem either imitating another or cloaking one. 

This is a nice truck — well worth the cost of an engine.

The Titan

The subject of today’s article — a 2005 Nissan Titan with 157,647 miles — hadn’t been driven for a while because the owner was certain that the engine was destroyed, and she wanted us to listen to it. She said her husband had driven it until the oil light came on and kept driving. That sounded serious, but we figured we’d evaluate it anyway. She left the truck one night after we were closed and gone and we looked at it the next morning. We initially noticed two things. First, before we even started the engine, we found that the oil wasn’t touching the stick, but it only took three quarts to put it on full, so it wasn’t low enough for engine damage, and she didn’t mention having added any oil.   

When we started the engine, it was rattling to beat the band in the bell housing area and leaking oil from the rear main so fast that it made a puddle nearly two feet in diameter within three minutes. Seldom do we see a pressure-driven leak that bad this side of a double-gasketed oil filter.

I have seen a lot of cracked flywheels, but this one took the cake for having been driven many a mile until it began radiating cracks from the bolt circle.

The noise sounded suspiciously like a cracked flywheel, but we didn’t hear anything else – that being said, how long do you want to let an engine run when it’s bleeding to death, and who could hear anything over that nasty rattling in the bell housing anyway? It was telegraphing all over the place. I called and suggested that she let us jerk the transmission out for some exploratory surgery, and she agreed. What we found was a very seriously cracked flywheel. Not only was it cracked around the bolt circle, it had cracks radiating toward the ring gear. This was a big noisemaker. A new flywheel from Nissan is only a little more than a hundred bucks, and we got her to agree to the flywheel and a rear main seal. We had also drained the transmission oil (which was kind of black), and she’d get the new red stuff too. This transmission has a metal screen that can be cleaned and reinstalled. Justin steam-cleaned the muddy transmission and the other parts in preparation for the reassembly, but the flywheel wouldn’t be in for a couple of days.

Altima engine swap   

About that time, we drew an engine swap job on a 2005 Altima that came in rattling like a diamondback, and the owner was savvy enough to have a replacement engine dropped off right after the car rolled in. Externally, the replacement mill was rusty on the steel and chalky on the aluminum - it looked like it had been sitting somewhere damp, but it turned easily with the breaker bar and there was no sludge we could see in the oil splash area through the filler cap hole, so we didn’t even yank the valve cover. It did get a rear main seal just for grins. I considered transferring the catalyst heat shield from the original engine, but those little bolts will usually snap when you try to remove them, so I left it be.

With these two grounds swinging, the Nissan would just sit there and spin, which isn’t particularly surprising. What’s worse is when the guilty ground is buried somewhere out of sight.

With everything disconnected and the powertrain sitting on the OTC lift, we decided to take the Autel scope camera and the MaxiSys we got from AE tools to have a look in the upstream O2 sensor hole at the brick, where we found at least part of the reason for the engine failure, and it’s a fairly common occurrence on these little rascals. That potential source of damage tends to be cloaked if you don’t look here. The catalyst on the bad motor looked like Bryce Canyon Utah on a moonlit night when we took our snapshot, and some of that brick dust must have made it through the remaining comb, into the EGR system, and back into the chambers. The early Ford SHO Taurus engines tended to have that problem too. Fortunately, the replacement engine’s cat had a nice healthy looking light-off honeycomb.

This was actually kind of funny – a guy down the hill who primarily does diesel nuts-and-bolts work made this connection and couldn’t figure out why it wouldn’t charge. The alternator was checked and found to be fine.

And every Altima veteran knows it’s a good idea to shove new cam and crank sensors in the used replacement engine, but we didn’t (why I still don’t know), and this time we got lucky, but at first, we didn’t think so. The replacement engine spun without fire and even showed moderate activity at the COP coils with the PICO wand, but then he found two small ground wires on the upper part of the timing cover he had left swinging, and when we got those in place we had fire in the holes, but after a few test drives we found that it would sometimes default to idle and throw TP sensor codes – it would need a throttle body – we had used the car’s original one when we sewed it up, because the on that came with the replacement engine had fallen prey to the elements and risking that one would be a bad bet. Even with a customer-supplied engine, that job wasn’t cheap at the end of the day, but today it’s back on the road.

The catalyst on the Altima was a nasty mess, and this isn’t uncommon on those vehicles. Fortunately, the replacement engine’s cat looked healthy, but a bolt-on replacement runs about $350 or so if needed.

The frozen Focus

The 2010 Focus belongs to a colleague, and her complaint was that she’d lose her air conditioning after driving awhile. One of the first things we noticed was that the suction line would become coated with ice. This was a freezer and we needed to know why. The evaporator thermistor likes to die and prevent A/C engagement on these Fusions, but could it possibly fail the other way? We had popped one in there last year, and she didn’t seem to have much trouble after that, but this past autumn the problem returned, and we broke out the IDS to see what we could see on the PID list. Measured with a thermometer, the register temperature would drop into the low twenties with the evaporator temperature reading hovering just below fifty degrees. What the heck was this all about?

The freezing evaporator was apparently blocking the airflow across the thermistor on this Fusion – it’s not in the heat exchanger like they used to be, and that created the confusion.

Let me go on record by saying that I absolutely love Identifix and wouldn’t be without it, but in this case, the I-fixers weren’t much help. A/C problems abound on Ford Fusions and it’s easy to get bogged down wading through all the posts – I put in a hotline request and the guy suggested installing a resistor in series with that NTC thermistor – higher resistance translates to a lower measured temperature. A very competent Ford tech I know suggested the same thing. Had it been done successfully before? I had no idea.

With everything sitting fallow and the control box out of the loop, the thermistor measured the right resistance for ambient temps. And while I could see the hotline guy’s logic I couldn’t figure out why it’d be necessary to add a component like that to a system that wasn’t built with it. Of course, there have been times in my career when I did stuff like that for troubleshooting purposes, and so that’s what I did this time, but nothing seemed to change. In the meantime, we also noticed that the blower was come-and-go and we had to replace the controller and its connector to take care of that problem – that’s another common malady on more than a few vehicles we saw last summer.

The Discharge sensor was what we found ourselves focusing on, but actually the easy-to-change pressure transducer was at fault – it stopped the freezing problem for good.

While we were fighting the Focus, a 2006 Pontiac G6 came in with a charging system that wouldn’t work. Well, as it turned out, somebody had worked on that one in the starter area and had connected the fuse-linked alternator charge wire to the solenoid post that fed the starter motor where nothing is supposed to be – the charge current from the alternator was never making it to the battery – it was apparently just slowly spinning the starter motor as the car was driven. That one was easy to find because there was no B+ measured at the big alternator terminal. It looked like somebody had put the charge wire on the terminal that was easiest to get to. Rookies do that sometimes.

This is the part number for the transducer on a 2010 Fusion in case you run into one of these.

My breakthrough on the Focus freezer came when Jimmie, one of my superstars at a nearby Ford dealer, ran into the same problem on a Fusion he was working on. After replacing that $20 thermistor and his Fusion still freezing up, he decided that the A/C pressure transducer was at fault (I had never seen this), and while he was ordering one for the car he was working on, I had him snag one for me. And since we changed out that $125 transducer our Fusion has had normal A/C. The part is easy to change. This cloak came from the fact that the actual temperature of the evaporator case plenum was skewed because the evaporator was freezing up and blocking airflow – rather than measuring the actual evaporator temperature the old fashioned way, the thermistor is measuring that open area, and for some reason it doesn’t read the temperature of the air that’s exiting the registers, thus this problem was cloaked by design, albeit not purposely. The IDS PID in this case wasn’t particularly friendly, nor was it helpful. One way or another, this one snowed us for a while.

Clash of the Titan

The flywheel came in for the Titan, and with the oil leak fixed and the transmission re-stabbed, it was the end of a long day. We started the engine and it didn’t leak oil and ran quietly, but we didn’t warm it up, nor did we test drive it that day. That would happen the next day, and when I spoke to the lady on the phone, I even told her that the jury was still out but that it looked like we had maybe dodged a bullet, but I told her I’d know more on the morrow. And I did.

Yeah, we should have checked this first. It was a bad call — and all mine — to go after that flywheel noise and that geyser of an oil leak. We never stop learning, it seems.

The bullet wasn’t dodged. When we started the engine the next day to test drive it, we heard a tattletale knock as soon as we dropped it in gear – and it wasn’t a good sound. Apparently, it had gone lower on oil than we had presumed, to the severe detriment of some bearings. At that point we pulled the sump pan to find two things. We found a partially clogged oil screen and slivers of engine life forces swimming in the sump. It wasn’t a good feeling, but the lady who owned the truck was surprisingly understanding – the flywheel had indeed needed replacing, but a replacement engine very probably would come with one anyway, and that 2010 truck is worth an engine. I even found her one for a good price, but she decided to put off the repair until she could feather out financially. They drove the truck away with the knock, and from what she told me, we’ll see her again when she gets an engine. It was a heck of a lot quieter and there were no oil leaks, but it still felt like we had dropped the ball – and I guess we did.


I was lamenting the experience with that Titan to my advisory committee, and several of them said they had experienced the same kind of pitfall – one serious problem cloaks another one to the point that the first fix isn’t the final one, and some customers are more understanding than others. And I don’t like this any more than the customer does. With 20/20 hindsight, I realized that we should have pulled the sump pan before we went after that flywheel, because it would have been easy to do, and the bad call was all mine. I suppose the vibrations from the flywheel coupled with that hard rear main seal must have been the perfect formula for making a pint-a-mile oil leak, especially with the bearing(s) hammered out. Well at least we got that oil leak fixed.

About the Author

Richard McCuistian

Richard McCuistian is an ASE certified Master Auto Technician and was a professional mechanic for more than 25 years, followed by 18 years as an automotive instructor at LBW Community College in Opp, AL. Richard is now retired from teaching and still works as a freelance writer for Motor Age and various Automotive Training groups.

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